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Development of formulated diets for snakehead (Channa striata and Channa micropeltes): Can phytase and taurine supplementation increase use of soybean meal to replace fish meal?
Aquaculture 448 (2015) 334–340
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Development of formulated diets for snakehead (Channa striata and Channa micropeltes): Can phytase and taurine supplementation increase use of soybean meal to replace fish meal? Tran Thi Thanh Hien a, Tran Thi Be a, Chong M. Lee b, David A. Bengtson c,⁎ a b c
College of Aquaculture and Fisheries, Can Tho University, Can Tho, Viet Nam Department of Nutrition and Food Sciences, University of Rhode Island, Kingston, RI 02881, USA Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, Kingston, RI 02881, USA
a r t i c l e
i n f o
Article history: Received 17 September 2013 Received in revised form 12 June 2015 Accepted 13 June 2015 Available online 16 June 2015 Keywords: Snakehead Diet Phytase Taurine Soybean meal Fish meal
a b s t r a c t Culture of snakehead species is limited in Vietnam and banned in Cambodia because of the reliance of the industry on feeding them “small-size” fish (sometimes called trash fish or low-value fish), many of which are juveniles of commercially important species. In an effort to find substitutes for small-size fish, we conducted a series of experiments to test formulated diets with several levels of soybean meal (SBM) replacement of fish meal. Feeding trials lasted eight weeks, after which survival, growth, food conversion ratio and protein efficiency ratio were compared. In the first two experiments, with Channa striata, we substituted SBM, either with or without supplementation of phytase (20 mg/kg) (Experiment 1) or taurine (1 g/kg) (Experiment 2), for 0, 20, 30, 40, or 50% of the fish meal. Experiment 1 demonstrated that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, phytase supplementation. Experiment 2 showed again that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, taurine supplementation. The third experiment, with Channa micropeltes, which was done only with phytase supplementation, showed that 40% of fish meal can be replaced by SBM. In all the SBM diets, the essential amino acids (EAA) lysine, methionine and threonine were also added to make their dietary levels equal to those in the fish meal control diet. Use of the SBM replacement diets, in addition to conserving the small-size fish in the wild, would result in economic savings (cost/kg of fish produced) of about 11% compared to diets based on fish meal alone. Statement of relevance: Aquaculture is growing rapidly in Vietnam and has the potential to do the same in Cambodia. Production of pangasiid catfish in the Mekong Delta of Vietnam alone exceeded 1 million metric tons in 2008. While some of the food provided to these fish, especially at the larger commercial farms, is formulated feed from commercial feed mills, many small farmers still use “trash fish” from the Mekong in preparing feed by hand at the farm. As aquaculture expands in Vietnam and Cambodia, the fish called snakehead is becoming popular to culture because of its high value in the market. Two species are cultured, the snakehead murrel, C. striata, and the giant snakehead, C. micropeltes. While culture of these is growing in Vietnam, it is prohibited in Cambodia (except for some experimental work) due to its dependence on small fish in the diet. Catfish culture has available commercial pellet diets, so getting farmers to switch from small fish to pellets is a socioeconomic issue, since small-scale catfish farmers often rely on traditional methods and the local availability of small fish. On the other hand, formulated diets do not yet exist for snakehead in Vietnam and Cambodia. © 2015 Published by Elsevier B.V.
1. Introduction Aquaculture is growing rapidly in Vietnam and has the potential to do the same in Cambodia. Production of pangasiid catfish in the Mekong Delta of Vietnam alone exceeded 1 million metric tons in 2008. While some of the food provided to these fish, especially at the larger commercial farms, is formulated feed from commercial feed mills, many small ⁎ Corresponding author. E-mail address: [email protected] (D.A. Bengtson).
http://dx.doi.org/10.1016/j.aquaculture.2015.06.020 0044-8486/© 2015 Published by Elsevier B.V.
farmers still use “trash fish” from the Mekong in preparing feed by hand at the farm. As aquaculture expands in Vietnam and Cambodia, the fish called snakehead is becoming popular to culture because of its high value in the market. Two species are cultured, the snakehead murrel, Channa striata, and the giant snakehead, Channa micropeltes. While culture of these is growing in Vietnam, it is prohibited in Cambodia (except for some experimental work) due to its dependence on small fish in the diet. Catfish culture has available commercial pellet diets, so getting farmers to switch from small fish to pellets is a socioeconomic issue, since small-scale catfish farmers often rely on traditional
T.T.T. Hien et al. / Aquaculture 448 (2015) 334–340
methods and the local availability of small fish. On the other hand, formulated diets do not yet exist for snakehead in Vietnam and Cambodia. Piscivorous fish like snakehead typically require high levels of protein in the diet, reflecting the high protein content in their natural diet. The usual source of that protein in pellet diets is fish meal (FM). Because of the high price of fish meal, and to reduce the fishing pressure on the species in industrial fisheries, fish nutritionists and aquaculturists worldwide are trying to replace fish meal with plant proteins in diets for fish. Soybean meal (SBM) is the most common fish meal-replacement source in aquafeeds, having one of the best amino acid profiles among plant protein sources (NRC, 1993), but it also contains some antinutritional compounds, such as phytic acid (NRC, 1993). As the hexaphosphate form of myo-inositol, phytic acid readily binds divalent cations, which creates problems in mineral nutrition, especially for freshwater fish (Lall, 2002). Many fish nutritionists have supplemented diets with phytase, to liberate free phosphorus from phytic acid, when significant portions of plant protein meals such as soybean meal are used in fish feeds. Phytase supplementation yielded positive results in several species, including channel catfish (Jackson et al., 1996), striped bass (Hughes and Soares, 1998), Atlantic salmon (Sajjadi and Carter, 2004), rainbow trout (Cheng et al., 2004), and Labeo rohita (Baruah et al., 2007). Replacement of fish meal with plant proteins alters the amino acid composition of fish diets. Thus, individual essential amino acids are often added to diets to make the amino acid composition of the plant diets equivalent to those of fish-meal diets or to meet the known or estimated requirements of the species being reared. Recently, researchers have found that taurine addition can also be beneficial (Gaylord et al., 2007). Taurine derives from methionine via cysteine and is not considered to be among the ten EAA's, nor is it incorporated into protein; however, it has several physiological roles and is relatively abundant in fish meal (Gaylord et al., 2007). The ability of fish to synthesize taurine is species dependent and the beneficial effects of dietary taurine supplementation have been demonstrated in many species (Matsunari et al., 2008). In sea bass fry, Dicentrarchus labrax, a taurine supplemented diet resulted in an increase in growth rate when FM and SBM were the primary sources of protein (Brotons Martinez et al., 2004). The overall objective of this study is the development of costeffective alternative feed for snakehead to replace or reduce the dependence on low value/trash fish. The results of this study are intended to provide information on alternative diets for snakehead, especially those diets that incorporate plant materials, in order to build a longterm sustainable industry. Through an economic analysis of costs of the diets (based on costs of fish meal and plant proteins vs. trash fish) and the risks of the unavailability of trash fish in the future, study results will allow decisions to be made by feed mills for local production of diets for the snakehead industry. The specific objectives of the study were to determine the appropriate SBM level to replace FM with and without phytase or taurine supplementation in snakehead diets (which already contained added EAA's to eliminate any differences from the FM control diet resulting from SBM inclusion). 2. Methodology 2.1. Experimental description Three experiments were conducted: Experiment 1 was a study of the replacement of FM by SBM (composition of FM and SBM is shown in Table 1) with EAA and phytase supplementation in diets for C. striata; Experiment 2 was a study of the replacement of FM by SBM with added EAA and taurine in diets for C. striata; Experiment 3 was a study of the replacement of FM by SBM with added EAA and phytase in diets for C. micropeltes. The same basal diets were used for both species. Price of ingredients is shown in Table 1.
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2.2. Experimental fish Fish used in these experiments were spawned from laboratory broodstock and reared prior to experimentation in the freshwater fish hatchery of the College of Aquaculture & Fisheries, Can Tho University, Vietnam. Before starting the experiments, all the fish were reared in 2000-L round tanks and were fed with trash fish combined with formulated diets for 4 weeks. Replacement of trash fish by formulated feed was applied gradually until 100% of trash fish was substituted by pellet feed. 2.3. Specific experimental designs In each of experiments 1 and 2, nine diet treatments were set up randomly in 27 experimental tanks (500-L composite tank) with three replicates for each treatment. Thirty C. striata fingerlings (4.74 ± 0.10 g in initial weight) were randomly assigned to each tank (experiments were run simultaneously). In experiment 3, five diet treatments were set up randomly in 15 experimental tanks (500-L composite tank) with three replicates for each treatment. C. micropeltes fingerlings (4.34 ± 0.07 g in initial weight) were randomly distributed into the 15 tanks with 25 individuals per tank. At the beginning of each experiment, 20 fingerlings from the stock tank were sacrificed for assessment of their initial proximate body composition. In addition, at the end of the experiment, all fish from each replicate were collected for the final proximate body composition analysis. During the trial, the fish were fed to apparent satiety by hand three times a day at 8:00, 12:00 and 17:00 h. Uneaten food was removed from the tank following feeding and the feed intake recorded based on the amount fed minus that recovered (on a dry weight basis following placement if a drying oven for at least 4 h at 105 °C). Total fish weight in each aquarium was determined every 4 weeks and dead fish were recorded and weighed daily. Water temperature, measured daily, ranged from 27.0–28.5 °C. pH and dissolved oxygen, measured weekly, varied from 7.0–7.2 and 5.0–7.6 ppm, respectively. Thirty percent of tank water was changed every three days. 2.3.1. Experiment 1 Nine practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of FM by SBM without phytase supplementation (FM, SBM-20, SBM-30, SBM-40 and SBM-50, respectively); and 20%, 30%, 40% and 50% with phytase addition (SBM-P-20, SBM-P-30, SBM-P-40 and SBM-P-50, respectively) on a protein equivalent basis in the diet. In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to make their levels equal to those in the FM control diet. All of the experimental diets were formulated to be isonitrogenous and isoenergetic and to contain 45% crude protein (CP) and 4.5 kcal gross energy/g of diet. Phytase (Ronozyme P-CT, dry powder; 5000 FTU) (DSM Nutritional Products, Basel, Switzerland) was added to the SBM-P diets at 0.2 g/kg feed One phytase unit (FTU) is the activity of phytase that generates 1 μmol of inorganic phosphorus per minute from sodium phytate. The level was chosen based on previous dietary SBM experiments with summer flounder (Paralichthys dentatus) at the University of Rhode Island (Lightbourne et al., in preparation). Composition of the experimental diets is shown in Table 1. 2.3.2. Experiment 2 Nine practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of FM by SBM without taurine addition (FM, SBM-20, SBM-30, SBM-40 and SBM-50, respectively); and 20%, 30%, 40% and 50% with taurine supplementation (SBM-T-20, SBM-T-30, SBM-T-40 and SBM-T-50, respectively) on a protein equivalent basis. In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to make their levels equal to those in the FM control diet. All of the experimental diets were formulated to be isonitrogenous and isoenergetic to contain 45% crude protein (CP) and 4.5 kcal gross
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Table 1 Composition and proximate analyses of the nine experimental diets (% of dry matter basis) used in the Channa striata phytase experiment (Expt 1). Diet abbreviations explained in text. Ingredients (%)
FM⁎
SBM-20
SBM-30
SBM-40
SBM-50
SBM-P-20
SBM-P-30
SBM-P-40
SBM-P-50
Fish meala Soybean mealb Starch Vitamin mixc Mineral mixd Fish oil Carboxymethylcellulose Lysine Methionine Threonine Phytase Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.34 0.190 0.142 0.097 – 100
41.77 26.12 17.90 2.00 2.00 5.68 3.89 0.285 0.213 0.145 – 100
35.80 34.82 15.05 2.00 2.00 6.03 3.44 0.380 0.284 0.194 – 100
29.83 43.53 12.26 2.00 2.00 6.37 2.93 0.475 0.356 0.242 – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.32 0.190 0.142 0.097 0.02 100
41.77 26.12 17.90 2.00 2.00 5.68 3.87 0.285 0.213 0.145 0.02 100
35.80 34.82 15.05 2.00 2.00 6.03 3.42 0.380 0.284 0.194 0.02 100
29.83 43.53 12.26 2.00 2.00 6.37 2.91 0.475 0.356 0.242 0.02 100
88.6 44.4 9.55 11.9 5.61 28.6 4.61
88.6 44.5 9.43 12.3 5.65 28.1 4.58
88.1 44.2 9.53 11.5 5.70 29.1 4.62
88.4 44.6 9.46 12.5 5.86 27.6 4.57
93.3 44.5 8.70 12.1 5.41 29.3 4.57
93.5 44.6 8.84 12.3 5.52 28.7 4.56
93.4 44.7 8.81 12.1 5.68 28.7 4.56
93.4 44.5 8.87 12.1 5.85 28.7 4.55
Proximate composition, dry weight basis (%) Dry matter 89.9 Crude protein 44.7 Crude lipid 9.14 Ash 12.9 Fiber – Nitrogen free extract 33.3 Gross energy (kcal/g) 4.78 a
FM: Kien Giang fishmeal was supplied by Minh Tam Co., Ltd (Vietnam). Moisture: 11.7%, crude protein: 65.1%, crude lipid: 7.94%, crude fiber: 0.55% and Ash:13.7%. SBM: Argentine Soybean meal was supplied by Quang Dung Co.,Ltd (Vietnam) Moisture: 8.78%, crude protein: 46,1%, crude lipid: 1,98%, crude fiber: 6.36% and Ash:6.20%. Vitamin mix consisted (UI kg−1 or g kg−1): vitamin A: 2.500.000UI: vitamin D3: 1.500.000UI, vitamin E: 80 g, vitamin B1: 800 mg, vitamin B2: 2000 mg, vitamin B6: 800 mg, vitamin B12: 20 mg, vitamin C: 8 g, vitamin K3: 1000 mg, Choline: 200 g, Niacin: 6.5 g, Folic acid: 250 mg, Biotin: 40 mg. d Mineral mix consisted of CuSO4: 10 g, ZnSO4: 20 g, MgSO4: 10 g, CoSO4: 1 g, FeSO4: 5 g, MnSO4 5 g, CaHPO4: 1 g. ⁎ Price of ingredients ($/kg): FM: 0.91, SBM: 0.36, Starch: 0.17, Vitamin: 1.94, Mineral: 1.37, Oil: 1.14, CMC: 1.71, Lysine: 1.83, Meth: 6.4, Ther: 6.8, Taurine: 1.83, Phytase:12.5. b c
energy/g of diet. Taurine was added at 1 g/kg of the diet. The level was chosen based on previous dietary SBM experiments with summer flounder (P. dentatus) at the University of Rhode Island (Lightbourne, 2011). Composition of the experimental diets is shown in Table 2.
2.3.3. Experiment 3 Five practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of the FM by SBM with phytase supplementation (FM, SBM-P-20, SBM-P-30, SBM-P-40 and SBM-P-50, respectively). In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to eliminate deficiencies caused by substitution of fish meal. All of the experimental diets were formulated to be isonitrogenous, 44% crude
protein, and isocaloric, 4.5 Kcal/g diet in gross energy. Phytase enzyme (Ronozyme, dry powder) was added to the SBM-P at 0.2 g/kg feed. Composition of the experimental diets is shown in Table 3. The experimental diets were made in a laboratory pellet mill by blending all of the dry ingredients with 300 ml water per kg dry ingredients. The extruding temperature did not exceed 40 °C. After extruding, all diets were dried at 45 °C within 48 h and stored at 4 °C prior to use.
2.4. Data calculation At the end of each experiment, fish were weighed and counted to calculate survival rate (SR), daily weight gain (DWG), feed intake (FI),
Table 2 Composition and proximate analyses of the nine experimental diets (% of dry matter basis) used in the Channa striata taurine experiment (Expt 2). NFE = nitrogen-free extract; GE = gross energy. Ingredients (%)
FM
SBM-20
SBM-30
SBM-40
SBM-50
SBM-T-20
SBM-T-30
SBM-T-40
SBM-T-50
Fish meal Soybean meal Starch Vitamin mixa Mineral mixb Fish oil CMC Lysine Methionine Threonine Taurine Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.34 0.190 0.142 0.097 – 100
41.77 26.12 17.90 2.00 2.00 5.68 3.89 0.285 0.213 0.145 – 100
35.80 34.82 15.05 2.00 2.00 6.03 3.44 0.380 0.284 0.194 – 100
29.83 43.53 12.26 2.00 2.00 6.37 2.93 0.475 0.356 0.242 – 100
47.74 17.41 20.75 2.00 2.00 5.33 3.34 0.190 0.142 0.097 1.00 100
41.77 26.12 17.90 2.00 2.00 5.68 2.89 0.285 0.213 0.145 1.00 100
35.80 34.82 15.05 2.00 2.00 6.03 2.44 0.380 0.284 0.194 1.00 100
29.83 43.53 12.26 2.00 2.00 6.37 1.93 0.475 0.356 0.242 1.00 100
88.6 44.5 9.43 12.3 5.65 28.1 4.58
88.1 44.2 9.53 11.5 5.70 29.1 4.62
88.4 44.6 9.46 12.5 5.86 27.6 4.57
88.9 44.4 8.52 11.9 5.34 29.8 4.56
88.3 44.3 8.39 12.4 5.44 29.5 4.35
89.1 44.6 8.37 12.7 5.64 28.7 4.52
89.8 44.6 8.53 12.0 5.68 29.1 4.54
Proximate composition, dry weight basis (%) Dry matter 89.9 88.6 Crude protein 44.7 44.4 Crude lipid 9.14 9.55 Ash 12.9 11.9 Fibre – 5.61 NFE 33.3 28.6 GE (kcal/g) 4.78 4.61 a b
See Table 1 for composition of vitamin mix. See Table 1 for composition of mineral mix.
T.T.T. Hien et al. / Aquaculture 448 (2015) 334–340 Table 3 Composition and proximate analyses of the five experimental diets (% of dry matter basis) used in the Channa micropeltes phytase experiment (Expt 3).
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(Gerhardt, Germany). This calculation is on a dry matter basis. Carbohydrate-NFE equals [100 − (CP + CL + CF + Ash)].
Ingredients (%)
FM
SBM-20
SBM-30
SBM-40
SBM-50
2.6. Statistical analysis
Fish meal Soybean meal Starch Vitamin mixa Mineral mixb Fish oil CMC Lysine Methionine Threonine Phytase Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.32 0.190 0.142 0.097 0.02 100
41.77 26.12 17.90 2.00 2.00 5.68 3.87 0.285 0.213 0.145 0.02 100
35.80 34.82 15.05 2.00 2.00 6.03 3.42 0.380 0.284 0.194 0.02 100
29.83 43.53 12.26 2.00 2.00 6.37 2.91 0.475 0.356 0.242 0.02 100
Data were checked for normal distribution by One-Sample Kolmogorov–Smirnov test and homogeneity of variances by Levene's test. Data were analyzed using One-way analysis of variance (One-way ANOVA) test followed by a Duncan's Multiple Range Test. Differences in growth and feed efficiency between diet treatments were considered to be statistically significant when p ≤ 0.05. The statistical tests were performed using the SPSS statistical package (ver. 16.0, SPSS Company, Chicago, IL, USA).
Proximate composition, (dry weight basis, %) Dry matter 89.9 93.3 Crude protein 44.7 44.5 Crude lipid 9.14 8.70 Ash 12.9 12.1 Fibre – 5.41 Nitrogen free extract 33.3 29.3 Gross energy (kcal/g) 4.78 4.57 a b
3. Results 93.5 44.6 8.84 12.3 5.52 28.7 4.56
93.4 44.7 8.81 12.1 5.68 28.7 4.56
93.4 44.5 8.87 12.1 5.85 28.7 4.55
See Table 1 for composition of vitamin mix. See Table 1 for composition of mineral mix.
feed conversion ratio (FCR), protein efficiency ratio (PER), and economic conversion ratio (ECR), where SR ¼ ðnumber of fish at end of experiment=number of fish at beginning of experimentÞ 100 DWG ¼ ðweight of fish at end of experiment−weight of fish at beginning of experimentÞ=days FI ¼ ðweight of feed consumed=number of fishÞ=days FCR ¼ weight of feed consumed=weight gain of fish PER ¼ weight gain of fish=weight of protein consumed ECR ¼ FCR feed cost:
2.5. Chemical analysis Moisture, crude protein, crude lipid, crude ash and nitrogen-free extracts were determined in fish collected at the beginning and end of each experiment. Proximate composition of experimental diets, initial and final body composition was estimated using standard methods (AOAC, 2000). To determine moisture, samples were weighed in a dried and weighed porcelain tumbler, then were desiccated in a drying oven (Gallenkamp, UK) at 105 °C for over 4 h (for dry samples) and 24 h (for wet samples) to constant weight. Loss on drying was used to determine moisture content. The sample in the porcelain tumbler was then incinerated in a muffle furnace (Gallenkamp, UK) at 600 °C for 6–8 h. The loss after incineration was considered as total ash. For crude fiber (CF) analysis, a fat-free sample was digested with boiling sulfuric acid (0.128 M; 1.25%, w/v) and subsequently by NaOH (0.313 M) in a fiber analyzer (Vela Scientific, Italia). The remaining residue was dried at 100 °C. This residue after subtraction of ash was regarded as fiber. Crude protein (CP) (N × 6.25) was determined by Kjeldahl method using three steps: digestion with concentrated sulfuric acid (H2SO4 98%), catalyst (H2O2) and high temperature by Kjeldahl digestion system (Gerhardt, Germany), distillation after reaction with NaOH (40%), and the released NH3 was absorbed by H3BO3 (2%) in the Kjeldahl distillation systems (Vapodest 10sn, Gerhardt, Germany), and manual titration by H2SO4 (0.01 N) (Merck, Germany). Gross energy (GE) content was determined with a 6100 Compensated Jacket Calorimeter (Parr Inst, USA). Crude lipid (CL) was extracted by petroleum ether at 60 °C for 6–8 h from the dried sample using Soxhlet extraction system
3.1. Survival and growth results 3.1.1. Experiment 1 There was no significant difference in survival rate among fish fed the different diets (Table 4). Final weight, weight gain, and daily weight gain of fish fed FM, SBM-20, SBM-30, SBM-P-20, SBM-P-30 and SBM-P-40 were not significantly different (Table 4). In contrast, the growth performances of fish fed SBM-40, SBM-50 and SBM-P-50 were significantly lower than those fed the control (FM) feed. FCR in fish fed SBM-50 was significantly greater than that of fish fed all the diets with less than 40% SBM replacement; all the other diets were not significantly different from each other (Table 4). Similarly, PER in fish fed the SBM-50 diet was significantly lower than that of fish fed FM, SBM-P-20 and SBM-30; all the other diets were not significantly different from each other (Table 4). 3.1.2. Experiment 2 There was no significant difference in survival rate of fish among diets (Table 5). In this experiment, the final weight and daily weight gain of fish fed FM, SBM-20, SBM-30, SBM-T-20, SBM-T-30 and SBM-T-40 were not significantly different; in contrast, the growth of fish fed SBM-40, SBM-50 and SBM-T-50 was significantly lower than that of fish fed control (FM) feed (Table 5). Feed intake (FI) data indicated significant differences only between fish fed the SBM-50 diet and those fed the FM, SBM-20, and SBM-T-20 diets. Feed conversion ratio (FCR) data indicated significant differences between both of the SBM 50% diets and all the diets up to 30% SBM, with the exception that the SBM-T-50 diet did not differ from the SBM-30 diet. Protein efficiency ratio (PER) data indicated differences between the SBM-50 diet and the FM diet, as well as between the SBM-T-50 diet and the SBM-T-20 diet (Table 5). 3.1.3. Experiment 3 Survival rate of fish among treatments was not significantly different (Table 6). Fish in the FM treatment showed significantly greater final weight and daily weight gain (0.38 ± 0.05 g ∙ day− 1) than those in the SBM-P-50 treatment (0.28 ± 0.01 g ∙ day− 1), but no significant differences from the other diets (Table 6). Significant differences in FCR and PER were seen only between the FM and SBM-P-50 treatments (Table 6). 3.2. Proximate composition of fish Proximate composition of fish fed the different diets in a given experiment showed few statistically significant differences (Table 7). In Experiment 1, crude protein content of fish fed diet SBM-P-30 was significantly greater than those of fish fed diets FM and SBM-40, and crude lipid of fish fed diet SBM-20 was significantly greater than those of fish fed diets SBM-P-30 and SBM-P-50.I. In Experiment 2, crude protein content of fish fed diet SBM-30 and SBM-50 were significantly
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Table 4 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio(PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa striata fed the nine experimental diets in the phytase experiment (Expt 1). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diets
Initial weight
FM SBM-20 SBM-P-20 SBM-30 SBM-P-30 SBM-40 SBM-P-40 SBM-50 SBM-P-50
4.79 ± 0.01 4.71 ± 0.02 4.70 ± 0.01 4.77 ± 0.03 4.71 ± 0.01 4.77 ± 0.09 4.74 ± 0.02 4.82 ± 0.05 4.77 ± 0.01
Final weight c
21.3 ± 2.04 19.6 ± 1.13bc 21.9 ± 1.08c 18.5 ± 1.36bc 19.5 ± 1.56bc 15.8 ± 0.98ab 19.4 ± 1.53bc 13.4 ± 0.17a 16.8 ± 0.38ab
DWG
SR c
0.28 ± 0.03 0.25 ± 0.02bc 0.29 ± 0.02c 0.23 ± 0.02bc 0.25 ± 0.03bc 0.18 ± 0.02ab 0.25 ± 0.03bc 0.14 ± 0.01a 0.20 ± 0.01ab
63.3 ± 1.93 56.7 ± 3.84 61.1 ± 4.02 54.5 ± 2.23 62.2 ± 4.00 57.8 ± 2.23 61.7 ± 0.95 54.4 ± 4.83 57.8 ± 4.00
FI
FCR bc
242.5 ± 10.7 213.2 ± 8.0bc 245.5 ± 13.5bc 192.0 ± 18.0bc 211.9 ± 5.4bc 185.0 ± 4.5b 257.8 ± 39.2c 124.8 ± 13.1a 198.9 ± 35.3bc
greater than that of fish fed diet SBM-T-40. In Experiment 3, crude lipid in fish fed diets SBM-P-40 and SBM-P-50 were significantly greater than those of fish fed diets SBM-P-20 and SBM-P-30, which in turn were significantly greater than that of fish fed diet FM, and ash content of fish fed diets FM and SBM-P-30 were significantly greater than that of fish fed diet SBM-P-50.
PER a
1.12 ± 0.16 1.16 ± 0.11a 1.07 ± 0.15a 1.21 ± 0.08a 1.12 ± 0.14a 1.51 ± 0.11ab 1.31 ± 0.02ab 1.78 ± 0.26b 1.40 ± 0.11ab
b
2.32 ± 0.30 2.24 ± 0.20ab 2.35 ± 0.37b 2.12 ± 0.14b 2.24 ± 0.34ab 1.72 ± 0.12ab 1.83 ± 0.03ab 1.48 ± 0.19a 1.75 ± 0.14ab
$/kg feed
$/kg fish
RED
0.799 0.754 0.756 0.732 0.734 0.71 0.712 0.687 0.689
0.894 0.867 0.794 0.791 0.822 1.015 0.933 1.127 0.965
– 3.0 11.2 11.5 8.1 −13.5 −4.4 −26.1 −7.9
transition. Nevertheless, the growth of the snakehead used in these experiments was less than that normally seen when snakehead (both C. micropeltes and C. striata) are fed on small-size fish (Chau, 2010; Toan, 2010). Further studies will be required to provide diets and feeding practices that farmers will want to use. Mortality of fish in Experiments 1 and 2 (C. striata) was quite high compared to that in Experiment 3 (C. micropeltes). We have observed generally that C. striata is much more aggressive toward conspecifics in a tank than is C. micropeltes, so we suspect that much of the mortality was due to these aggressive encounters. Studies with other species have often shown limited ability to replace FM with SBM, e.g., 30–58% replacement of FM in Paralichthys olivaceus (Saitoh et al., 2003; Choi et al., 2005), 40% in Myxocyprinus asiaticus (Yu et al., 2013), but up to 83% in Morone chrysops × Morone saxatilis hybrids (Rombenso et al., 2013). Many investigators have reported that the supplementation of phytase to P-inadequate diets enhances growth performance. Soltan et al. (2008) studied the maximum replacement levels of FM by a plant protein mixture (cottonseed, sunflower, canola, sesame and linseed meals) in diets for Nile tilapia and found that up to 45% of FM can be replaced with no significant reduction in growth rate from that on the control diet. An increase of weight gain has been reported in channel catfish fed phytase supplemented diets containing only plant protein or a combination of plant and animal protein sources (Jackson et al., 1996). The supplemental effect of phytase on growth performance in fish cannot be directly compared because it may differ depending on fish species and rearing conditions, and more specifically on dietary composition in each feeding study (Cao et al., 2007). Generally, growth improvements have been observed in studies that used plant-based diets supplemented with phytase; however, results have been somewhat inconsistent (Cao et al., 2007). Oddly, assuming that increased phosphorus availability would lead to increased bone formation, no significant differences were seen in ash content of C. striata with phytase supplementation, although ash content of C. micropeltes did decrease significantly with greater levels of SBM inclusion when all SBM diets had phytase supplementation.
3.3. Economic analysis From an economic point of view, replacing up to 30% of FM by SBM with phytase supplementation in diets for C. striata achieved an economic benefit; however, the greatest gains were seen in the SBM-P-20 diet (Table 4). Similarly, it can be seen that replacing up to 30% of FM by SBM with taurine supplementation in diets for C. striata achieved an economic benefit (Table 5). Cost for one kg fish weight gain was reduced by a maximum of 11.5% in treatment SBM-30 compared to the control treatment. Finally, replacing up to 50% of FM by SBM with phytase supplementation in diets for C. micropeltes also achieved an economic benefit (Table 6). Cost for one kg fish weight gain was reduced 4.2% in treatment SBM-P-40 compared to control (FM) treatment. 4. Discussion This is the first demonstration that FM in diets for C. striata and C. micropeltes fingerlings diets can be replaced by SBM without affecting the growth performances, feed utilizations and survival of the two species. Up to 40% of fish meal can be replaced, as long as phytase and the EAA's lysine, methionine and threonin are added to the diet, or up to 30% can be replaced if only those EAA's are added. We assume that the phytase caused phosphates to be released from their phytin binders, thus making phosphorus more available to the fish. This is a useful step in the quest to change the habits of the snakehead aquaculture industry away from reliance on small-size fish. The fact that there are economic benefits as well from substituting SBM for FM should aid the industry
Table 5 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio (PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa striata fed the nine experimental diets in the taurine experiment (Expt 2). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diets
Initial weight
Final weight
DWG
SR
FI
FCR
PER
$/kg feed
$/kg fish
RED
FM SBM-20 SBM-T-20 SBM-30 SBM-T-30 SBM-40 SBM-T-40 SBM-50 SBM-T-50
4.79 ± 0.01 4.71 ± 0.02 4.69 ± 0.01 4.77 ± 0.03 4.68 ± 0.01 4.77 ± 0.09 4.64 ± 0.16 4.82 ± 0.05 4.77 ± 0.08
21.3 ± 2.04de 19.6 ± 1.13bcde 22.6 ± 1.07e 18.5 ± 1.36bcd 19.3 ± 1.73bcde 15.8 ± 0.98abc 17.6 ± 0.42bcd 13.4 ± 0.17a 15.6 ± 0.32ab
0.28 ± 0.03cd 0.25 ± 0.02cd 0.30 ± 0.02d 0.23 ± 0.02bc 0.24 ± 0.03bcd 0.18 ± 0.02ab 0.21 ± 0.01bc 0.14 ± 0.01a 0.18 ± 0.01ab
63.3 ± 1.93 56.7 ± 3.84 53.3 ± 3.84 54.5 ± 2.23 53.3 ± 1.93 57.8 ± 2.23 53.3 ± 3.33 54.4 ± 4.83 55.0 ± 0.98
242.5 ± 10.7b 213.2 ± 8.0b 254.0 ± 47.3b 192.0 ± 18.0ab 198.2 ± 19.8ab 185.0 ± 4.5ab 196.7 ± 42.4ab 124.8 ± 13.1a 195.2 ± 8.1ab
1.12 ± 0.16a 1.16 ± 0.11a 1.11 ± 0.17a 1.21 ± 0.08ab 1.15 ± 0.04a 1.51 ± 0.11abc 1.33 ± 0.25abc 1.78 ± 0.26c 1.68 ± 0.02bc
2.32 ± 0.30c 2.24 ± 0.20abc 2.29 ± 0.36bc 2.12 ± 0.14abc 2.11 ± 0.07abc 1.72 ± 0.12abc 1.98 ± 0.45abc 1.48 ± 0.19ab 1.43 ± 0.01a
0.799 0.754 0.755 0.732 0.733 0.71 0.711 0.687 0.688
0.894 0.867 0.839 0.791 0.843 1.015 0.946 1.127 1.156
– 3.0 6.2 11.5 5.7 −13.5 −5.8 −26.1 −29.3
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Table 6 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio (PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa micropeltes fed the five experimental diets in the phytase experiment (Expt 3). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Treatment FM SBM-P-20 SBM-P-30 SBM-P-40 SBM-P-50
Initial weight 4.34 ± 0.08 4.30 ± 0.03 4.40 ± 0.03 4.32 ± 0.03 4.33 ± 0.04
Final weight b
25.6 ± 2.45 23.2 ± 1.18ab 21.9 ± 1.23ab 21.1 ± 1.14ab 20.3 ± 0.94a
DWG
SR b
0.38 ± 0.05 0.34 ± 0.02ab 0.31 ± 0.02ab 0.30 ± 0.02ab 0.28 ± 0.01a
77.3 ± 8.74 78.7 ± 3.53 78.7 ± 5.81 80.0 ± 4.00 77.3 ± 7.42
Although taurine supplementation allowed slightly, but not significantly higher growth at the level of 40% FM replacement with SBM, the economic benefits were actually reduced at the 40% level (with or without taurine) compared to the control. Thus, we cannot argue that taurine should be used in snakehead diets. Most previous studies on taurine supplementation in conjunction with plant protein replacement of FM have focused on marine fish species, such as P. olivaceus (Park et al., 2002), D. labrax (Brotons Martinez et al., 2004), and Rachycentron canadum (Lunger et al., 2007), although the freshwater rainbow trout Oncorhynchus mykiss also benefited from taurine supplementation when they were fed an all-plant diet (Gaylord et al., 2006). Taurine is thought to be important for osmoregulation by marine fish, so perhaps the need for it by freshwater snakeheads in the Mekong River and Delta is not so critical physiologically. While our results have been encouraging, we plan to continue our studies with multiple approaches to the study of replacing small-size fish with formulated feeds in snakehead diets. We will experiment with diets that contain plant proteins more easily obtainable than SBM in Southeast Asia, we will try other supplemental products in SBM diets, and we will experiment with feeding strategies that use a mixture of small-size fish and formulated feeds. In addition, further Table 7 Proximate composition (%), as is basis, in carcass of snakehead (Channa striata in experiments 1 and 2; Channa micropeltes in experiment 3) fed experimental diets in the three experiments. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diet
Moisture
Crude protein
Crude lipid
Ash
Experiment 1 Initial FM SBM-20 SBM-P-20 SBM-30 SBM-P-30 SBM-40 SBM-P-40 SBM-50 SBM-P-50
78.8 ± 0.36 73.4 ± 0.64 73.0 ± 1.28 74.0 ± 0.17 73.5 ± 0.47 74.1 ± 0.30 73.8 ± 0.19 74.1 ± 0.72 73.1 ± 0.28 74.3 ± 0.98
13.8 ± 0.15 15.4 ± 0.13a 15.7 ± 0.27a,b 15.7 ± 0.35a,b 15.9 ± 0.15a,b 16.3 ± 0.03b 15.5 ± 0.12a 15.8 ± 0.15a,b 15.9 ± 0.36a,b 15.6 ± 0.09a,b
1.36 ± 0.02 4.36 ± 0.11a,b 4.71 ± 0.06b 4.49 ± 0.21a,b 4.40 ± 0.01a,b 4.29 ± 0.05a 4.46 ± 0.09a,b 4.39 ± 0.11a,b 4.57 ± 0.21a,b 4.26 ± 0.03a
4.75 ± 0.12 4.76 ± 0.06 4.75 ± 0.50 4.67 ± 0.32 4.87 ± 0.40 4.70 ± 0.35 4.51 ± 0.10 4.64 ± 0.23 4.95 ± 0.23 4.47 ± 0.18
Experiment 2 Initial FM SBM-20 SBM-T-20 SBM-30 SBM-T-30 SBM-40 SBM-T-40 SBM-50 SBM-T-50
78.8 ± 0.36 73.4 ± 0.64 73.0 ± 1.28 73.0 ± 0.20 73.5 ± 0.47 73.1 ± 0.27 73.8 ± 0.19 74.0 ± 0.74 73.0 ± 0.20 73.1 ± 0.27
13.8 ± 0.15 15.4 ± 0.13a,b 15.7 ± 0.27a,b 15.5 ± 0.03a,b 15.9 ± 0.15b 15.5 ± 0.01a,b 15.5 ± 0.12a,b 15.0 ± 0.06a 15.9 ± 0.26b 15.4 ± 0.35a,b
1.36 ± 0.02 4.36 ± 0.11 4.71 ± 0.06 4.65 ± 0.43 4.40 ± 0.01 4.44 ± 0.06 4.46 ± 0.09 4.35 ± 0.03 4.57 ± 0.21 4.67 ± 0.03
4.75 ± 0.12 4.76 ± 0.06 4.75 ± 0.50 4.67 ± 0.73 4.87 ± 0.40 4.79 ± 0.12 4.51 ± 0.10 4.78 ± 0.44 4.95 ± 0.23 4.84 ± 0.05
Experiment 3 Initial FM SBM-P-20 SBM-P-30 SBM-P-40 SBM-P-50
79.5 77.2 ± 0.23 77.4 ± 0.93 77.1 ± 0.81 77.2 ± 0.57 76.9 ± 0.20
12.2 14.2 ± 0.14 13.7 ± 0.55 13.6 ± 0.31 13.8 ± 0.40 14.0 ± 0.12
1.78 2.39 ± 0.01a 2.86 ± 0.16b 2.88 ± 0.10b 3.63 ± 0.14c 3.67 ± 0.08c
5.97 4.94 ± 0.09b 4.42 ± 0.54ab 4.74 ± 0.42b 3.79 ± 0.39ab 3.50 ± 0.10a
FI
FCR
427.9 ± 54.2 390.9 ± 11.7 371.1 ± 23.8 359.0 ± 18.9 351.0 ± 21.7
PER a
1.20 ± 0.06 1.25 ± 0.06ab 1.28 ± 0.01ab 1.29 ± 0.03ab 1.34 ± 0.01b
b
2.08 ± 0.11 1.94 ± 0.10ab 1.87 ± 0.02ab 1.87 ± 0.04ab 1.79 ± 0.01a
$/kg feed
$/kg fish
RED
0.799 0.754 0.732 0.71 0.687
0.96 0.94 0.94 0.92 0.93
– 2.1 2.1 4.2 3.1
studies will be required to elucidate the physiological bases for growth improvements seen with phytase addition to snakehead diets. Acknowledgments This research was funded by the AquaFish CRSP under USAID CA/ LWA No. EPP-A-00-06-00012-00 and by US and Host Country partners. The AquaFish CRSP accession number is 1377. The opinions expressed herein are those of the author(s) and do not necessarily reflect the views of the AquaFish CRSP or the US Agency for International Development. References AOAC, 2000. Official Methods of Analysis International. 17th ed. Association of Official Analytical Chemists, Gaithersburg, Md. Baruah, K., Pal, A.K., Sahu, N.P., Debnath, D., 2007. Microbial phytase supplementation in rohu, Labeo rohita, diet enhances growth performance and nutrient digestibility. J. World Aquacult. Soc. 38, 129–137. Brotons Martinez, J., Chatzifotis, S., Divanach, P., Takeuchi, T., 2004. Effect of dietary taurine supplementation on growth performance and feed selection of sea bass fry fed with demand feeders. Fish. Sci. 70, 74–79. Cao, L., Wang, W., Yang, C., Yang, Y., Diana, J., Yakupitiyage, A., Luo, Z., Li, D., 2007. Application of microbial phytase in fish feed. Enzym. Microb. Technol. 40, 497–507. Chau, V.M.Q., 2010. Replacement of Fish Meal and Soybean Meal by Rice Bran in Snakehead (Channa striata, Bloch 1793) diets (Master's thesis), College of Aquaculture and Fisheries, Can Tho University, Vietnam (in Vietnamese). Cheng, Z.J., Hardy, R.W., Verlhac, V., Gabaudan, J., 2004. Effect of microbial phytase supplementation and dosage on apparent digestibility coefficients of nutrients and dry matter in soybean product-based diets for rainbow trout Oncorhynchus mykiss. J. World Aquacult. Soc. 35, 1–15. Choi, S.M., Xiaojie, W., Park, G.-J., Lim, S.R., Kim, K.W., Bai, S.C., Shin, I.S., 2005. Dietary dehulled soybean meal as a replacement for fish meal in fingerling and growing olive flounder Paralichthys olivaceus (Temminck and Schlegel). Aquac. Res. 35, 410–418. Gaylord, T.G., Teague, A., Barrow, F., 2006. Taurine supplementation of all-plant protein diets for rainbow trout (Oncorhynchus mykiss). J. World Aquacult. Soc. 37, 509–517. Gaylord, T.G., Barrows, F.T., Teague, A.M., Johansen, K.A., Overturf, K.E., Shepherd, B., 2007. Supplementation of taurine and methionine to all-plant protein diets for rainbow trout (Oncorhynchus mykiss). Aquaculture 269, 514–524. Hughes, K.P., Soares Jr., J.P., 1998. Efficacy of phytase on phosphorus utilization in practical diets fed to striped bass Morone saxatilis. Aquac. Nutr. 4, 133–140. Jackson, L.S., Li, M.H., Robinson, E.H., 1996. Use of microbial phytase in channel catfish Ictalurus punctatus diets to improve utilization of phytate phosphorus1. J. World Aquacult. Soc. 27, 309–313. Lall, S.P., 2002. The Minerals. In: Halver, J.E., Hardy, R.W. (Eds.), Fish Nutrition, 3rd ed. Academic Press, San Diego, USA, pp. 259–308. Lightbourne, C., 2011. Effects of Soybean Meal Replacement with Added Taurine in Fish Meal Diets for Summer Flounder (Parallichthys dentatus) (M.S. Thesis), University of Rhode Island (55 pp.). Lightbourne, C., Bengtson, D.A., Gomez-Chiarri, M., Volson, B., Karayannakidis, P.D., Lee, C.M., 2015. Partial Replacement of Fish Meal with Soybean Meal in Diets for Summer Flounder, Paralichthys dentatus: Effects of Addition of Taurine and Phytase on Survival, Growth, Response to Bacterial Challenge, and Product Quality (in preparation). Lunger, A.N., McLean, E., Gaylord, T.G., Kuhn, D., Craig, S.R., 2007. Taurine supplementation to alternative dietary proteins used in fish meal replacement enhances growth of juvenile cobia (Rachycentron canadum). Aquaculture 271, 401–410. Matsunari, H., Yamamoto, T., Kim, S.K., Goto, T., Takeuchi, T., 2008. Optimum dietary taurine level in casein-based diet for juvenile red sea bream. Pagrus major. Fish. Sci. 74, 347–353. National Research Council (NRC), 1993. Nutrient Requirements of Fish. National Academy Press, Washington, DC, USA (71 pp.). Park, G.S., Takeuchi, T., Yokoyama, M., Seikai, T., 2002. Optimal dietary taurine level for growth of juvenile Japanese flounder (Paralichthys olivaceus). Fish. Sci. 68, 824–829. Rombenso, A., Crouse, C., Trushenski, J., 2013. Comparison of traditional and fermented soybean meals as alternatives to fish meal in hybrid striped bass feeds. N. Am. J. Aquac. 75, 197–204.
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Development of formulated diets for snakehead (Channa striata and Channa micropeltes): Can phytase and taurine supplementation increase use of soybean meal to replace fish meal? Tran Thi Thanh Hien a, Tran Thi Be a, Chong M. Lee b, David A. Bengtson c,⁎ a b c
College of Aquaculture and Fisheries, Can Tho University, Can Tho, Viet Nam Department of Nutrition and Food Sciences, University of Rhode Island, Kingston, RI 02881, USA Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, Kingston, RI 02881, USA
a r t i c l e
i n f o
Article history: Received 17 September 2013 Received in revised form 12 June 2015 Accepted 13 June 2015 Available online 16 June 2015 Keywords: Snakehead Diet Phytase Taurine Soybean meal Fish meal
a b s t r a c t Culture of snakehead species is limited in Vietnam and banned in Cambodia because of the reliance of the industry on feeding them “small-size” fish (sometimes called trash fish or low-value fish), many of which are juveniles of commercially important species. In an effort to find substitutes for small-size fish, we conducted a series of experiments to test formulated diets with several levels of soybean meal (SBM) replacement of fish meal. Feeding trials lasted eight weeks, after which survival, growth, food conversion ratio and protein efficiency ratio were compared. In the first two experiments, with Channa striata, we substituted SBM, either with or without supplementation of phytase (20 mg/kg) (Experiment 1) or taurine (1 g/kg) (Experiment 2), for 0, 20, 30, 40, or 50% of the fish meal. Experiment 1 demonstrated that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, phytase supplementation. Experiment 2 showed again that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, taurine supplementation. The third experiment, with Channa micropeltes, which was done only with phytase supplementation, showed that 40% of fish meal can be replaced by SBM. In all the SBM diets, the essential amino acids (EAA) lysine, methionine and threonine were also added to make their dietary levels equal to those in the fish meal control diet. Use of the SBM replacement diets, in addition to conserving the small-size fish in the wild, would result in economic savings (cost/kg of fish produced) of about 11% compared to diets based on fish meal alone. Statement of relevance: Aquaculture is growing rapidly in Vietnam and has the potential to do the same in Cambodia. Production of pangasiid catfish in the Mekong Delta of Vietnam alone exceeded 1 million metric tons in 2008. While some of the food provided to these fish, especially at the larger commercial farms, is formulated feed from commercial feed mills, many small farmers still use “trash fish” from the Mekong in preparing feed by hand at the farm. As aquaculture expands in Vietnam and Cambodia, the fish called snakehead is becoming popular to culture because of its high value in the market. Two species are cultured, the snakehead murrel, C. striata, and the giant snakehead, C. micropeltes. While culture of these is growing in Vietnam, it is prohibited in Cambodia (except for some experimental work) due to its dependence on small fish in the diet. Catfish culture has available commercial pellet diets, so getting farmers to switch from small fish to pellets is a socioeconomic issue, since small-scale catfish farmers often rely on traditional methods and the local availability of small fish. On the other hand, formulated diets do not yet exist for snakehead in Vietnam and Cambodia. © 2015 Published by Elsevier B.V.
1. Introduction Aquaculture is growing rapidly in Vietnam and has the potential to do the same in Cambodia. Production of pangasiid catfish in the Mekong Delta of Vietnam alone exceeded 1 million metric tons in 2008. While some of the food provided to these fish, especially at the larger commercial farms, is formulated feed from commercial feed mills, many small ⁎ Corresponding author. E-mail address: [email protected] (D.A. Bengtson).
http://dx.doi.org/10.1016/j.aquaculture.2015.06.020 0044-8486/© 2015 Published by Elsevier B.V.
farmers still use “trash fish” from the Mekong in preparing feed by hand at the farm. As aquaculture expands in Vietnam and Cambodia, the fish called snakehead is becoming popular to culture because of its high value in the market. Two species are cultured, the snakehead murrel, Channa striata, and the giant snakehead, Channa micropeltes. While culture of these is growing in Vietnam, it is prohibited in Cambodia (except for some experimental work) due to its dependence on small fish in the diet. Catfish culture has available commercial pellet diets, so getting farmers to switch from small fish to pellets is a socioeconomic issue, since small-scale catfish farmers often rely on traditional
T.T.T. Hien et al. / Aquaculture 448 (2015) 334–340
methods and the local availability of small fish. On the other hand, formulated diets do not yet exist for snakehead in Vietnam and Cambodia. Piscivorous fish like snakehead typically require high levels of protein in the diet, reflecting the high protein content in their natural diet. The usual source of that protein in pellet diets is fish meal (FM). Because of the high price of fish meal, and to reduce the fishing pressure on the species in industrial fisheries, fish nutritionists and aquaculturists worldwide are trying to replace fish meal with plant proteins in diets for fish. Soybean meal (SBM) is the most common fish meal-replacement source in aquafeeds, having one of the best amino acid profiles among plant protein sources (NRC, 1993), but it also contains some antinutritional compounds, such as phytic acid (NRC, 1993). As the hexaphosphate form of myo-inositol, phytic acid readily binds divalent cations, which creates problems in mineral nutrition, especially for freshwater fish (Lall, 2002). Many fish nutritionists have supplemented diets with phytase, to liberate free phosphorus from phytic acid, when significant portions of plant protein meals such as soybean meal are used in fish feeds. Phytase supplementation yielded positive results in several species, including channel catfish (Jackson et al., 1996), striped bass (Hughes and Soares, 1998), Atlantic salmon (Sajjadi and Carter, 2004), rainbow trout (Cheng et al., 2004), and Labeo rohita (Baruah et al., 2007). Replacement of fish meal with plant proteins alters the amino acid composition of fish diets. Thus, individual essential amino acids are often added to diets to make the amino acid composition of the plant diets equivalent to those of fish-meal diets or to meet the known or estimated requirements of the species being reared. Recently, researchers have found that taurine addition can also be beneficial (Gaylord et al., 2007). Taurine derives from methionine via cysteine and is not considered to be among the ten EAA's, nor is it incorporated into protein; however, it has several physiological roles and is relatively abundant in fish meal (Gaylord et al., 2007). The ability of fish to synthesize taurine is species dependent and the beneficial effects of dietary taurine supplementation have been demonstrated in many species (Matsunari et al., 2008). In sea bass fry, Dicentrarchus labrax, a taurine supplemented diet resulted in an increase in growth rate when FM and SBM were the primary sources of protein (Brotons Martinez et al., 2004). The overall objective of this study is the development of costeffective alternative feed for snakehead to replace or reduce the dependence on low value/trash fish. The results of this study are intended to provide information on alternative diets for snakehead, especially those diets that incorporate plant materials, in order to build a longterm sustainable industry. Through an economic analysis of costs of the diets (based on costs of fish meal and plant proteins vs. trash fish) and the risks of the unavailability of trash fish in the future, study results will allow decisions to be made by feed mills for local production of diets for the snakehead industry. The specific objectives of the study were to determine the appropriate SBM level to replace FM with and without phytase or taurine supplementation in snakehead diets (which already contained added EAA's to eliminate any differences from the FM control diet resulting from SBM inclusion). 2. Methodology 2.1. Experimental description Three experiments were conducted: Experiment 1 was a study of the replacement of FM by SBM (composition of FM and SBM is shown in Table 1) with EAA and phytase supplementation in diets for C. striata; Experiment 2 was a study of the replacement of FM by SBM with added EAA and taurine in diets for C. striata; Experiment 3 was a study of the replacement of FM by SBM with added EAA and phytase in diets for C. micropeltes. The same basal diets were used for both species. Price of ingredients is shown in Table 1.
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2.2. Experimental fish Fish used in these experiments were spawned from laboratory broodstock and reared prior to experimentation in the freshwater fish hatchery of the College of Aquaculture & Fisheries, Can Tho University, Vietnam. Before starting the experiments, all the fish were reared in 2000-L round tanks and were fed with trash fish combined with formulated diets for 4 weeks. Replacement of trash fish by formulated feed was applied gradually until 100% of trash fish was substituted by pellet feed. 2.3. Specific experimental designs In each of experiments 1 and 2, nine diet treatments were set up randomly in 27 experimental tanks (500-L composite tank) with three replicates for each treatment. Thirty C. striata fingerlings (4.74 ± 0.10 g in initial weight) were randomly assigned to each tank (experiments were run simultaneously). In experiment 3, five diet treatments were set up randomly in 15 experimental tanks (500-L composite tank) with three replicates for each treatment. C. micropeltes fingerlings (4.34 ± 0.07 g in initial weight) were randomly distributed into the 15 tanks with 25 individuals per tank. At the beginning of each experiment, 20 fingerlings from the stock tank were sacrificed for assessment of their initial proximate body composition. In addition, at the end of the experiment, all fish from each replicate were collected for the final proximate body composition analysis. During the trial, the fish were fed to apparent satiety by hand three times a day at 8:00, 12:00 and 17:00 h. Uneaten food was removed from the tank following feeding and the feed intake recorded based on the amount fed minus that recovered (on a dry weight basis following placement if a drying oven for at least 4 h at 105 °C). Total fish weight in each aquarium was determined every 4 weeks and dead fish were recorded and weighed daily. Water temperature, measured daily, ranged from 27.0–28.5 °C. pH and dissolved oxygen, measured weekly, varied from 7.0–7.2 and 5.0–7.6 ppm, respectively. Thirty percent of tank water was changed every three days. 2.3.1. Experiment 1 Nine practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of FM by SBM without phytase supplementation (FM, SBM-20, SBM-30, SBM-40 and SBM-50, respectively); and 20%, 30%, 40% and 50% with phytase addition (SBM-P-20, SBM-P-30, SBM-P-40 and SBM-P-50, respectively) on a protein equivalent basis in the diet. In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to make their levels equal to those in the FM control diet. All of the experimental diets were formulated to be isonitrogenous and isoenergetic and to contain 45% crude protein (CP) and 4.5 kcal gross energy/g of diet. Phytase (Ronozyme P-CT, dry powder; 5000 FTU) (DSM Nutritional Products, Basel, Switzerland) was added to the SBM-P diets at 0.2 g/kg feed One phytase unit (FTU) is the activity of phytase that generates 1 μmol of inorganic phosphorus per minute from sodium phytate. The level was chosen based on previous dietary SBM experiments with summer flounder (Paralichthys dentatus) at the University of Rhode Island (Lightbourne et al., in preparation). Composition of the experimental diets is shown in Table 1. 2.3.2. Experiment 2 Nine practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of FM by SBM without taurine addition (FM, SBM-20, SBM-30, SBM-40 and SBM-50, respectively); and 20%, 30%, 40% and 50% with taurine supplementation (SBM-T-20, SBM-T-30, SBM-T-40 and SBM-T-50, respectively) on a protein equivalent basis. In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to make their levels equal to those in the FM control diet. All of the experimental diets were formulated to be isonitrogenous and isoenergetic to contain 45% crude protein (CP) and 4.5 kcal gross
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Table 1 Composition and proximate analyses of the nine experimental diets (% of dry matter basis) used in the Channa striata phytase experiment (Expt 1). Diet abbreviations explained in text. Ingredients (%)
FM⁎
SBM-20
SBM-30
SBM-40
SBM-50
SBM-P-20
SBM-P-30
SBM-P-40
SBM-P-50
Fish meala Soybean mealb Starch Vitamin mixc Mineral mixd Fish oil Carboxymethylcellulose Lysine Methionine Threonine Phytase Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.34 0.190 0.142 0.097 – 100
41.77 26.12 17.90 2.00 2.00 5.68 3.89 0.285 0.213 0.145 – 100
35.80 34.82 15.05 2.00 2.00 6.03 3.44 0.380 0.284 0.194 – 100
29.83 43.53 12.26 2.00 2.00 6.37 2.93 0.475 0.356 0.242 – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.32 0.190 0.142 0.097 0.02 100
41.77 26.12 17.90 2.00 2.00 5.68 3.87 0.285 0.213 0.145 0.02 100
35.80 34.82 15.05 2.00 2.00 6.03 3.42 0.380 0.284 0.194 0.02 100
29.83 43.53 12.26 2.00 2.00 6.37 2.91 0.475 0.356 0.242 0.02 100
88.6 44.4 9.55 11.9 5.61 28.6 4.61
88.6 44.5 9.43 12.3 5.65 28.1 4.58
88.1 44.2 9.53 11.5 5.70 29.1 4.62
88.4 44.6 9.46 12.5 5.86 27.6 4.57
93.3 44.5 8.70 12.1 5.41 29.3 4.57
93.5 44.6 8.84 12.3 5.52 28.7 4.56
93.4 44.7 8.81 12.1 5.68 28.7 4.56
93.4 44.5 8.87 12.1 5.85 28.7 4.55
Proximate composition, dry weight basis (%) Dry matter 89.9 Crude protein 44.7 Crude lipid 9.14 Ash 12.9 Fiber – Nitrogen free extract 33.3 Gross energy (kcal/g) 4.78 a
FM: Kien Giang fishmeal was supplied by Minh Tam Co., Ltd (Vietnam). Moisture: 11.7%, crude protein: 65.1%, crude lipid: 7.94%, crude fiber: 0.55% and Ash:13.7%. SBM: Argentine Soybean meal was supplied by Quang Dung Co.,Ltd (Vietnam) Moisture: 8.78%, crude protein: 46,1%, crude lipid: 1,98%, crude fiber: 6.36% and Ash:6.20%. Vitamin mix consisted (UI kg−1 or g kg−1): vitamin A: 2.500.000UI: vitamin D3: 1.500.000UI, vitamin E: 80 g, vitamin B1: 800 mg, vitamin B2: 2000 mg, vitamin B6: 800 mg, vitamin B12: 20 mg, vitamin C: 8 g, vitamin K3: 1000 mg, Choline: 200 g, Niacin: 6.5 g, Folic acid: 250 mg, Biotin: 40 mg. d Mineral mix consisted of CuSO4: 10 g, ZnSO4: 20 g, MgSO4: 10 g, CoSO4: 1 g, FeSO4: 5 g, MnSO4 5 g, CaHPO4: 1 g. ⁎ Price of ingredients ($/kg): FM: 0.91, SBM: 0.36, Starch: 0.17, Vitamin: 1.94, Mineral: 1.37, Oil: 1.14, CMC: 1.71, Lysine: 1.83, Meth: 6.4, Ther: 6.8, Taurine: 1.83, Phytase:12.5. b c
energy/g of diet. Taurine was added at 1 g/kg of the diet. The level was chosen based on previous dietary SBM experiments with summer flounder (P. dentatus) at the University of Rhode Island (Lightbourne, 2011). Composition of the experimental diets is shown in Table 2.
2.3.3. Experiment 3 Five practical diets were formulated to replace 0%, 20%, 30%, 40% and 50% of the FM by SBM with phytase supplementation (FM, SBM-P-20, SBM-P-30, SBM-P-40 and SBM-P-50, respectively). In addition, the EAA's lysine, threonine and methionine were added to the SBM diets to eliminate deficiencies caused by substitution of fish meal. All of the experimental diets were formulated to be isonitrogenous, 44% crude
protein, and isocaloric, 4.5 Kcal/g diet in gross energy. Phytase enzyme (Ronozyme, dry powder) was added to the SBM-P at 0.2 g/kg feed. Composition of the experimental diets is shown in Table 3. The experimental diets were made in a laboratory pellet mill by blending all of the dry ingredients with 300 ml water per kg dry ingredients. The extruding temperature did not exceed 40 °C. After extruding, all diets were dried at 45 °C within 48 h and stored at 4 °C prior to use.
2.4. Data calculation At the end of each experiment, fish were weighed and counted to calculate survival rate (SR), daily weight gain (DWG), feed intake (FI),
Table 2 Composition and proximate analyses of the nine experimental diets (% of dry matter basis) used in the Channa striata taurine experiment (Expt 2). NFE = nitrogen-free extract; GE = gross energy. Ingredients (%)
FM
SBM-20
SBM-30
SBM-40
SBM-50
SBM-T-20
SBM-T-30
SBM-T-40
SBM-T-50
Fish meal Soybean meal Starch Vitamin mixa Mineral mixb Fish oil CMC Lysine Methionine Threonine Taurine Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.34 0.190 0.142 0.097 – 100
41.77 26.12 17.90 2.00 2.00 5.68 3.89 0.285 0.213 0.145 – 100
35.80 34.82 15.05 2.00 2.00 6.03 3.44 0.380 0.284 0.194 – 100
29.83 43.53 12.26 2.00 2.00 6.37 2.93 0.475 0.356 0.242 – 100
47.74 17.41 20.75 2.00 2.00 5.33 3.34 0.190 0.142 0.097 1.00 100
41.77 26.12 17.90 2.00 2.00 5.68 2.89 0.285 0.213 0.145 1.00 100
35.80 34.82 15.05 2.00 2.00 6.03 2.44 0.380 0.284 0.194 1.00 100
29.83 43.53 12.26 2.00 2.00 6.37 1.93 0.475 0.356 0.242 1.00 100
88.6 44.5 9.43 12.3 5.65 28.1 4.58
88.1 44.2 9.53 11.5 5.70 29.1 4.62
88.4 44.6 9.46 12.5 5.86 27.6 4.57
88.9 44.4 8.52 11.9 5.34 29.8 4.56
88.3 44.3 8.39 12.4 5.44 29.5 4.35
89.1 44.6 8.37 12.7 5.64 28.7 4.52
89.8 44.6 8.53 12.0 5.68 29.1 4.54
Proximate composition, dry weight basis (%) Dry matter 89.9 88.6 Crude protein 44.7 44.4 Crude lipid 9.14 9.55 Ash 12.9 11.9 Fibre – 5.61 NFE 33.3 28.6 GE (kcal/g) 4.78 4.61 a b
See Table 1 for composition of vitamin mix. See Table 1 for composition of mineral mix.
T.T.T. Hien et al. / Aquaculture 448 (2015) 334–340 Table 3 Composition and proximate analyses of the five experimental diets (% of dry matter basis) used in the Channa micropeltes phytase experiment (Expt 3).
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(Gerhardt, Germany). This calculation is on a dry matter basis. Carbohydrate-NFE equals [100 − (CP + CL + CF + Ash)].
Ingredients (%)
FM
SBM-20
SBM-30
SBM-40
SBM-50
2.6. Statistical analysis
Fish meal Soybean meal Starch Vitamin mixa Mineral mixb Fish oil CMC Lysine Methionine Threonine Phytase Total
59.67 0.00 26.45 2.00 2.00 4.64 5.24 – – – – 100
47.74 17.41 20.75 2.00 2.00 5.33 4.32 0.190 0.142 0.097 0.02 100
41.77 26.12 17.90 2.00 2.00 5.68 3.87 0.285 0.213 0.145 0.02 100
35.80 34.82 15.05 2.00 2.00 6.03 3.42 0.380 0.284 0.194 0.02 100
29.83 43.53 12.26 2.00 2.00 6.37 2.91 0.475 0.356 0.242 0.02 100
Data were checked for normal distribution by One-Sample Kolmogorov–Smirnov test and homogeneity of variances by Levene's test. Data were analyzed using One-way analysis of variance (One-way ANOVA) test followed by a Duncan's Multiple Range Test. Differences in growth and feed efficiency between diet treatments were considered to be statistically significant when p ≤ 0.05. The statistical tests were performed using the SPSS statistical package (ver. 16.0, SPSS Company, Chicago, IL, USA).
Proximate composition, (dry weight basis, %) Dry matter 89.9 93.3 Crude protein 44.7 44.5 Crude lipid 9.14 8.70 Ash 12.9 12.1 Fibre – 5.41 Nitrogen free extract 33.3 29.3 Gross energy (kcal/g) 4.78 4.57 a b
3. Results 93.5 44.6 8.84 12.3 5.52 28.7 4.56
93.4 44.7 8.81 12.1 5.68 28.7 4.56
93.4 44.5 8.87 12.1 5.85 28.7 4.55
See Table 1 for composition of vitamin mix. See Table 1 for composition of mineral mix.
feed conversion ratio (FCR), protein efficiency ratio (PER), and economic conversion ratio (ECR), where SR ¼ ðnumber of fish at end of experiment=number of fish at beginning of experimentÞ 100 DWG ¼ ðweight of fish at end of experiment−weight of fish at beginning of experimentÞ=days FI ¼ ðweight of feed consumed=number of fishÞ=days FCR ¼ weight of feed consumed=weight gain of fish PER ¼ weight gain of fish=weight of protein consumed ECR ¼ FCR feed cost:
2.5. Chemical analysis Moisture, crude protein, crude lipid, crude ash and nitrogen-free extracts were determined in fish collected at the beginning and end of each experiment. Proximate composition of experimental diets, initial and final body composition was estimated using standard methods (AOAC, 2000). To determine moisture, samples were weighed in a dried and weighed porcelain tumbler, then were desiccated in a drying oven (Gallenkamp, UK) at 105 °C for over 4 h (for dry samples) and 24 h (for wet samples) to constant weight. Loss on drying was used to determine moisture content. The sample in the porcelain tumbler was then incinerated in a muffle furnace (Gallenkamp, UK) at 600 °C for 6–8 h. The loss after incineration was considered as total ash. For crude fiber (CF) analysis, a fat-free sample was digested with boiling sulfuric acid (0.128 M; 1.25%, w/v) and subsequently by NaOH (0.313 M) in a fiber analyzer (Vela Scientific, Italia). The remaining residue was dried at 100 °C. This residue after subtraction of ash was regarded as fiber. Crude protein (CP) (N × 6.25) was determined by Kjeldahl method using three steps: digestion with concentrated sulfuric acid (H2SO4 98%), catalyst (H2O2) and high temperature by Kjeldahl digestion system (Gerhardt, Germany), distillation after reaction with NaOH (40%), and the released NH3 was absorbed by H3BO3 (2%) in the Kjeldahl distillation systems (Vapodest 10sn, Gerhardt, Germany), and manual titration by H2SO4 (0.01 N) (Merck, Germany). Gross energy (GE) content was determined with a 6100 Compensated Jacket Calorimeter (Parr Inst, USA). Crude lipid (CL) was extracted by petroleum ether at 60 °C for 6–8 h from the dried sample using Soxhlet extraction system
3.1. Survival and growth results 3.1.1. Experiment 1 There was no significant difference in survival rate among fish fed the different diets (Table 4). Final weight, weight gain, and daily weight gain of fish fed FM, SBM-20, SBM-30, SBM-P-20, SBM-P-30 and SBM-P-40 were not significantly different (Table 4). In contrast, the growth performances of fish fed SBM-40, SBM-50 and SBM-P-50 were significantly lower than those fed the control (FM) feed. FCR in fish fed SBM-50 was significantly greater than that of fish fed all the diets with less than 40% SBM replacement; all the other diets were not significantly different from each other (Table 4). Similarly, PER in fish fed the SBM-50 diet was significantly lower than that of fish fed FM, SBM-P-20 and SBM-30; all the other diets were not significantly different from each other (Table 4). 3.1.2. Experiment 2 There was no significant difference in survival rate of fish among diets (Table 5). In this experiment, the final weight and daily weight gain of fish fed FM, SBM-20, SBM-30, SBM-T-20, SBM-T-30 and SBM-T-40 were not significantly different; in contrast, the growth of fish fed SBM-40, SBM-50 and SBM-T-50 was significantly lower than that of fish fed control (FM) feed (Table 5). Feed intake (FI) data indicated significant differences only between fish fed the SBM-50 diet and those fed the FM, SBM-20, and SBM-T-20 diets. Feed conversion ratio (FCR) data indicated significant differences between both of the SBM 50% diets and all the diets up to 30% SBM, with the exception that the SBM-T-50 diet did not differ from the SBM-30 diet. Protein efficiency ratio (PER) data indicated differences between the SBM-50 diet and the FM diet, as well as between the SBM-T-50 diet and the SBM-T-20 diet (Table 5). 3.1.3. Experiment 3 Survival rate of fish among treatments was not significantly different (Table 6). Fish in the FM treatment showed significantly greater final weight and daily weight gain (0.38 ± 0.05 g ∙ day− 1) than those in the SBM-P-50 treatment (0.28 ± 0.01 g ∙ day− 1), but no significant differences from the other diets (Table 6). Significant differences in FCR and PER were seen only between the FM and SBM-P-50 treatments (Table 6). 3.2. Proximate composition of fish Proximate composition of fish fed the different diets in a given experiment showed few statistically significant differences (Table 7). In Experiment 1, crude protein content of fish fed diet SBM-P-30 was significantly greater than those of fish fed diets FM and SBM-40, and crude lipid of fish fed diet SBM-20 was significantly greater than those of fish fed diets SBM-P-30 and SBM-P-50.I. In Experiment 2, crude protein content of fish fed diet SBM-30 and SBM-50 were significantly
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Table 4 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio(PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa striata fed the nine experimental diets in the phytase experiment (Expt 1). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diets
Initial weight
FM SBM-20 SBM-P-20 SBM-30 SBM-P-30 SBM-40 SBM-P-40 SBM-50 SBM-P-50
4.79 ± 0.01 4.71 ± 0.02 4.70 ± 0.01 4.77 ± 0.03 4.71 ± 0.01 4.77 ± 0.09 4.74 ± 0.02 4.82 ± 0.05 4.77 ± 0.01
Final weight c
21.3 ± 2.04 19.6 ± 1.13bc 21.9 ± 1.08c 18.5 ± 1.36bc 19.5 ± 1.56bc 15.8 ± 0.98ab 19.4 ± 1.53bc 13.4 ± 0.17a 16.8 ± 0.38ab
DWG
SR c
0.28 ± 0.03 0.25 ± 0.02bc 0.29 ± 0.02c 0.23 ± 0.02bc 0.25 ± 0.03bc 0.18 ± 0.02ab 0.25 ± 0.03bc 0.14 ± 0.01a 0.20 ± 0.01ab
63.3 ± 1.93 56.7 ± 3.84 61.1 ± 4.02 54.5 ± 2.23 62.2 ± 4.00 57.8 ± 2.23 61.7 ± 0.95 54.4 ± 4.83 57.8 ± 4.00
FI
FCR bc
242.5 ± 10.7 213.2 ± 8.0bc 245.5 ± 13.5bc 192.0 ± 18.0bc 211.9 ± 5.4bc 185.0 ± 4.5b 257.8 ± 39.2c 124.8 ± 13.1a 198.9 ± 35.3bc
greater than that of fish fed diet SBM-T-40. In Experiment 3, crude lipid in fish fed diets SBM-P-40 and SBM-P-50 were significantly greater than those of fish fed diets SBM-P-20 and SBM-P-30, which in turn were significantly greater than that of fish fed diet FM, and ash content of fish fed diets FM and SBM-P-30 were significantly greater than that of fish fed diet SBM-P-50.
PER a
1.12 ± 0.16 1.16 ± 0.11a 1.07 ± 0.15a 1.21 ± 0.08a 1.12 ± 0.14a 1.51 ± 0.11ab 1.31 ± 0.02ab 1.78 ± 0.26b 1.40 ± 0.11ab
b
2.32 ± 0.30 2.24 ± 0.20ab 2.35 ± 0.37b 2.12 ± 0.14b 2.24 ± 0.34ab 1.72 ± 0.12ab 1.83 ± 0.03ab 1.48 ± 0.19a 1.75 ± 0.14ab
$/kg feed
$/kg fish
RED
0.799 0.754 0.756 0.732 0.734 0.71 0.712 0.687 0.689
0.894 0.867 0.794 0.791 0.822 1.015 0.933 1.127 0.965
– 3.0 11.2 11.5 8.1 −13.5 −4.4 −26.1 −7.9
transition. Nevertheless, the growth of the snakehead used in these experiments was less than that normally seen when snakehead (both C. micropeltes and C. striata) are fed on small-size fish (Chau, 2010; Toan, 2010). Further studies will be required to provide diets and feeding practices that farmers will want to use. Mortality of fish in Experiments 1 and 2 (C. striata) was quite high compared to that in Experiment 3 (C. micropeltes). We have observed generally that C. striata is much more aggressive toward conspecifics in a tank than is C. micropeltes, so we suspect that much of the mortality was due to these aggressive encounters. Studies with other species have often shown limited ability to replace FM with SBM, e.g., 30–58% replacement of FM in Paralichthys olivaceus (Saitoh et al., 2003; Choi et al., 2005), 40% in Myxocyprinus asiaticus (Yu et al., 2013), but up to 83% in Morone chrysops × Morone saxatilis hybrids (Rombenso et al., 2013). Many investigators have reported that the supplementation of phytase to P-inadequate diets enhances growth performance. Soltan et al. (2008) studied the maximum replacement levels of FM by a plant protein mixture (cottonseed, sunflower, canola, sesame and linseed meals) in diets for Nile tilapia and found that up to 45% of FM can be replaced with no significant reduction in growth rate from that on the control diet. An increase of weight gain has been reported in channel catfish fed phytase supplemented diets containing only plant protein or a combination of plant and animal protein sources (Jackson et al., 1996). The supplemental effect of phytase on growth performance in fish cannot be directly compared because it may differ depending on fish species and rearing conditions, and more specifically on dietary composition in each feeding study (Cao et al., 2007). Generally, growth improvements have been observed in studies that used plant-based diets supplemented with phytase; however, results have been somewhat inconsistent (Cao et al., 2007). Oddly, assuming that increased phosphorus availability would lead to increased bone formation, no significant differences were seen in ash content of C. striata with phytase supplementation, although ash content of C. micropeltes did decrease significantly with greater levels of SBM inclusion when all SBM diets had phytase supplementation.
3.3. Economic analysis From an economic point of view, replacing up to 30% of FM by SBM with phytase supplementation in diets for C. striata achieved an economic benefit; however, the greatest gains were seen in the SBM-P-20 diet (Table 4). Similarly, it can be seen that replacing up to 30% of FM by SBM with taurine supplementation in diets for C. striata achieved an economic benefit (Table 5). Cost for one kg fish weight gain was reduced by a maximum of 11.5% in treatment SBM-30 compared to the control treatment. Finally, replacing up to 50% of FM by SBM with phytase supplementation in diets for C. micropeltes also achieved an economic benefit (Table 6). Cost for one kg fish weight gain was reduced 4.2% in treatment SBM-P-40 compared to control (FM) treatment. 4. Discussion This is the first demonstration that FM in diets for C. striata and C. micropeltes fingerlings diets can be replaced by SBM without affecting the growth performances, feed utilizations and survival of the two species. Up to 40% of fish meal can be replaced, as long as phytase and the EAA's lysine, methionine and threonin are added to the diet, or up to 30% can be replaced if only those EAA's are added. We assume that the phytase caused phosphates to be released from their phytin binders, thus making phosphorus more available to the fish. This is a useful step in the quest to change the habits of the snakehead aquaculture industry away from reliance on small-size fish. The fact that there are economic benefits as well from substituting SBM for FM should aid the industry
Table 5 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio (PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa striata fed the nine experimental diets in the taurine experiment (Expt 2). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diets
Initial weight
Final weight
DWG
SR
FI
FCR
PER
$/kg feed
$/kg fish
RED
FM SBM-20 SBM-T-20 SBM-30 SBM-T-30 SBM-40 SBM-T-40 SBM-50 SBM-T-50
4.79 ± 0.01 4.71 ± 0.02 4.69 ± 0.01 4.77 ± 0.03 4.68 ± 0.01 4.77 ± 0.09 4.64 ± 0.16 4.82 ± 0.05 4.77 ± 0.08
21.3 ± 2.04de 19.6 ± 1.13bcde 22.6 ± 1.07e 18.5 ± 1.36bcd 19.3 ± 1.73bcde 15.8 ± 0.98abc 17.6 ± 0.42bcd 13.4 ± 0.17a 15.6 ± 0.32ab
0.28 ± 0.03cd 0.25 ± 0.02cd 0.30 ± 0.02d 0.23 ± 0.02bc 0.24 ± 0.03bcd 0.18 ± 0.02ab 0.21 ± 0.01bc 0.14 ± 0.01a 0.18 ± 0.01ab
63.3 ± 1.93 56.7 ± 3.84 53.3 ± 3.84 54.5 ± 2.23 53.3 ± 1.93 57.8 ± 2.23 53.3 ± 3.33 54.4 ± 4.83 55.0 ± 0.98
242.5 ± 10.7b 213.2 ± 8.0b 254.0 ± 47.3b 192.0 ± 18.0ab 198.2 ± 19.8ab 185.0 ± 4.5ab 196.7 ± 42.4ab 124.8 ± 13.1a 195.2 ± 8.1ab
1.12 ± 0.16a 1.16 ± 0.11a 1.11 ± 0.17a 1.21 ± 0.08ab 1.15 ± 0.04a 1.51 ± 0.11abc 1.33 ± 0.25abc 1.78 ± 0.26c 1.68 ± 0.02bc
2.32 ± 0.30c 2.24 ± 0.20abc 2.29 ± 0.36bc 2.12 ± 0.14abc 2.11 ± 0.07abc 1.72 ± 0.12abc 1.98 ± 0.45abc 1.48 ± 0.19ab 1.43 ± 0.01a
0.799 0.754 0.755 0.732 0.733 0.71 0.711 0.687 0.688
0.894 0.867 0.839 0.791 0.843 1.015 0.946 1.127 1.156
– 3.0 6.2 11.5 5.7 −13.5 −5.8 −26.1 −29.3
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Table 6 Initial and final weights (g ∙ fish−1), daily weight gain (DWG) (g ∙ day−1), survival rate (SR) (%), feed intake (FI) (mg ∙ fish−1 ∙ day−1), feed conversion ratio (FCR), protein efficiency ratio (PER) (protein gain−1) and costs for producing 1 kg of feed ($/kg feed) and for producing 1 kg of fish weight gain ($/kg fish), both in US$, of Channa micropeltes fed the five experimental diets in the phytase experiment (Expt 3). RED = percentage reduction in $/kg fish compared to control diet. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Treatment FM SBM-P-20 SBM-P-30 SBM-P-40 SBM-P-50
Initial weight 4.34 ± 0.08 4.30 ± 0.03 4.40 ± 0.03 4.32 ± 0.03 4.33 ± 0.04
Final weight b
25.6 ± 2.45 23.2 ± 1.18ab 21.9 ± 1.23ab 21.1 ± 1.14ab 20.3 ± 0.94a
DWG
SR b
0.38 ± 0.05 0.34 ± 0.02ab 0.31 ± 0.02ab 0.30 ± 0.02ab 0.28 ± 0.01a
77.3 ± 8.74 78.7 ± 3.53 78.7 ± 5.81 80.0 ± 4.00 77.3 ± 7.42
Although taurine supplementation allowed slightly, but not significantly higher growth at the level of 40% FM replacement with SBM, the economic benefits were actually reduced at the 40% level (with or without taurine) compared to the control. Thus, we cannot argue that taurine should be used in snakehead diets. Most previous studies on taurine supplementation in conjunction with plant protein replacement of FM have focused on marine fish species, such as P. olivaceus (Park et al., 2002), D. labrax (Brotons Martinez et al., 2004), and Rachycentron canadum (Lunger et al., 2007), although the freshwater rainbow trout Oncorhynchus mykiss also benefited from taurine supplementation when they were fed an all-plant diet (Gaylord et al., 2006). Taurine is thought to be important for osmoregulation by marine fish, so perhaps the need for it by freshwater snakeheads in the Mekong River and Delta is not so critical physiologically. While our results have been encouraging, we plan to continue our studies with multiple approaches to the study of replacing small-size fish with formulated feeds in snakehead diets. We will experiment with diets that contain plant proteins more easily obtainable than SBM in Southeast Asia, we will try other supplemental products in SBM diets, and we will experiment with feeding strategies that use a mixture of small-size fish and formulated feeds. In addition, further Table 7 Proximate composition (%), as is basis, in carcass of snakehead (Channa striata in experiments 1 and 2; Channa micropeltes in experiment 3) fed experimental diets in the three experiments. Data are means of three observations ± SEM. Means in the same column with the same superscript are not significantly different (P b 0.05). Diet
Moisture
Crude protein
Crude lipid
Ash
Experiment 1 Initial FM SBM-20 SBM-P-20 SBM-30 SBM-P-30 SBM-40 SBM-P-40 SBM-50 SBM-P-50
78.8 ± 0.36 73.4 ± 0.64 73.0 ± 1.28 74.0 ± 0.17 73.5 ± 0.47 74.1 ± 0.30 73.8 ± 0.19 74.1 ± 0.72 73.1 ± 0.28 74.3 ± 0.98
13.8 ± 0.15 15.4 ± 0.13a 15.7 ± 0.27a,b 15.7 ± 0.35a,b 15.9 ± 0.15a,b 16.3 ± 0.03b 15.5 ± 0.12a 15.8 ± 0.15a,b 15.9 ± 0.36a,b 15.6 ± 0.09a,b
1.36 ± 0.02 4.36 ± 0.11a,b 4.71 ± 0.06b 4.49 ± 0.21a,b 4.40 ± 0.01a,b 4.29 ± 0.05a 4.46 ± 0.09a,b 4.39 ± 0.11a,b 4.57 ± 0.21a,b 4.26 ± 0.03a
4.75 ± 0.12 4.76 ± 0.06 4.75 ± 0.50 4.67 ± 0.32 4.87 ± 0.40 4.70 ± 0.35 4.51 ± 0.10 4.64 ± 0.23 4.95 ± 0.23 4.47 ± 0.18
Experiment 2 Initial FM SBM-20 SBM-T-20 SBM-30 SBM-T-30 SBM-40 SBM-T-40 SBM-50 SBM-T-50
78.8 ± 0.36 73.4 ± 0.64 73.0 ± 1.28 73.0 ± 0.20 73.5 ± 0.47 73.1 ± 0.27 73.8 ± 0.19 74.0 ± 0.74 73.0 ± 0.20 73.1 ± 0.27
13.8 ± 0.15 15.4 ± 0.13a,b 15.7 ± 0.27a,b 15.5 ± 0.03a,b 15.9 ± 0.15b 15.5 ± 0.01a,b 15.5 ± 0.12a,b 15.0 ± 0.06a 15.9 ± 0.26b 15.4 ± 0.35a,b
1.36 ± 0.02 4.36 ± 0.11 4.71 ± 0.06 4.65 ± 0.43 4.40 ± 0.01 4.44 ± 0.06 4.46 ± 0.09 4.35 ± 0.03 4.57 ± 0.21 4.67 ± 0.03
4.75 ± 0.12 4.76 ± 0.06 4.75 ± 0.50 4.67 ± 0.73 4.87 ± 0.40 4.79 ± 0.12 4.51 ± 0.10 4.78 ± 0.44 4.95 ± 0.23 4.84 ± 0.05
Experiment 3 Initial FM SBM-P-20 SBM-P-30 SBM-P-40 SBM-P-50
79.5 77.2 ± 0.23 77.4 ± 0.93 77.1 ± 0.81 77.2 ± 0.57 76.9 ± 0.20
12.2 14.2 ± 0.14 13.7 ± 0.55 13.6 ± 0.31 13.8 ± 0.40 14.0 ± 0.12
1.78 2.39 ± 0.01a 2.86 ± 0.16b 2.88 ± 0.10b 3.63 ± 0.14c 3.67 ± 0.08c
5.97 4.94 ± 0.09b 4.42 ± 0.54ab 4.74 ± 0.42b 3.79 ± 0.39ab 3.50 ± 0.10a
FI
FCR
427.9 ± 54.2 390.9 ± 11.7 371.1 ± 23.8 359.0 ± 18.9 351.0 ± 21.7
PER a
1.20 ± 0.06 1.25 ± 0.06ab 1.28 ± 0.01ab 1.29 ± 0.03ab 1.34 ± 0.01b
b
2.08 ± 0.11 1.94 ± 0.10ab 1.87 ± 0.02ab 1.87 ± 0.04ab 1.79 ± 0.01a
$/kg feed
$/kg fish
RED
0.799 0.754 0.732 0.71 0.687
0.96 0.94 0.94 0.92 0.93
– 2.1 2.1 4.2 3.1
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