Production performance of Labeo calbasu (Hamilton) in polyculture with three Indian major carps Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) with provision of fertilizers, feed and periphytic substrate as varied inputs

Aquaculture 262 (2007) 333 – 339 www.elsevier.com/locate/aqua-online

Production performance of Labeo calbasu (Hamilton) in polyculture with three Indian major carps Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) with provision of fertilizers, feed and periphytic substrate as varied inputs P.K. Sahu 1 , J.K. Jena ⁎, P.C. Das, S. Mondal, R. Das Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar 751002, India Received 15 June 2006; received in revised form 17 November 2006; accepted 17 November 2006

Abstract Inclusion of kalbasu, Labeo calbasu as a candidate species in the Indian major carps based polyculture system was evaluated through a six-month grow-out trial in earthen ponds of 0.08 ha each. Species performance was assessed through provision of varied inputs viz., fertilizers (T-1), fertilizers + supplementary feed (T-2) and fertilizers + supplementary feed + periphytic substrate (T-3) as the three treatments, which were evaluated in replicates. Catla (35%), rohu (35%), mrigal (15%) and kalbasu (15%) were stocked at combined density of 7500 fingerlings/ha. While ponds were fertilized with cowdung, urea and single super phosphate, mixture of groundnut oilcake and rice bran at 1:1 (w/w) was provided as supplementary feed. The periphytic substrate, comprised stripe bamboo mat, was provided at 10% of the pond surface area. Provision of each additional input caused significantly higher increase in overall mean survival, growth, SGR and net biomass yield of carps. Among the carp species, while only rohu and kalbasu showed significantly higher weight gain (234.4 g and 170.3 g, respectively) in T-3, no such increase was noticed either in catla or mrigal. The net production in T-3 (1516.1 ± 24.3 kg ha− 1 6 months− 1) was 13.0 and 73.2% higher than those of T-2 (1341.7 ± 15.5 kg ha− 1 6 months− 1) and T-1 (875.2 ± 15.6 kg ha− 1 6 months− 1), respectively. The study revealed the relative advantage of using periphytic substrates in carp polyculture systems with kalbasu as a component species. © 2006 Elsevier B.V. All rights reserved. Keywords: Labeo calbasu; Indian major carps; Periphyton; Grow-out culture; Species diversification

1. Introduction The high consumer preference and wide distribution in major riverine systems and reservoirs in India have ⁎ Corresponding author. Tel.: +91 674 2465421; fax: +91 674 2465407. E-mail address: [email protected] (J.K. Jena). 1 Present address: Rice-Fish Unit, Central Rice Research Institute, Cuttack 753 006, India. 0044-8486/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2006.11.016

placed kalbasu, Labeo calbasu, as the most important carp species next to the three Indian major carps, i.e., catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala) (Chondar, 1999). Emphasis on species diversification (Kutty, 1999), in recent years, has placed kalbasu as a promising candidate species for inclusion in carp polyculture systems. Though the species formed a component in certain experimental grow-out trials (Aravindakshan et al., 1999; Wahab et al., 1999a; Tripathi et al., 2000), inadequacy in its

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seed availability and information on culture probably have restricted its incorporation into the commercial carp polyculture system in the country. The importance of fertilizers and supplementary feed in enhancing fish production in commercial carp polyculture has been well documented (Chaudhuri et al., 1975; Nandeesha, 1993). Use of periphytic substrate has also shown to be an important input for increasing the fish production through enhancement of the inherent productivity of pond. The association of microorganisms, algae and planktonic organisms attached as periphyton not only serve as food for fishes, but also act as in situ water purifier ensuring better living condition. Though higher yield through use of artificial substrate has been reported in the traditional capture fisheries such as Acadja Fisheries in West Africa (Welcomme, 1972) and brush pack of Sri Lanka (Senanayake, 1981), the benefit of using such substrate in commercial carp polyculture is yet to be explored. Higher growth of rohu and kalbasu has been reported in periphyton-based aquaculture using bamboo substrate and its products (Wahab et al., 1999a; Azim et al., 2001b, 2002, 2004; van Dam et al., 2002). Although many of these above studies on provision of periphytic substrate were carried out with carps, none of them dealt with incorporation of kalbasu along with the typical combination of catla, rohu and mrigal in carp polyculture. The present grow-out trial was an attempt to include kalbasu as a candidate species in Indian major carp based polyculture system and to evaluate performance of the species with different input combinations

of fertilizers, supplementary feed and periphytic substrate. 2. Materials and methods The grow-out experiment was conducted for six months, during February–June, 2005, in six ponds of 0.08 ha (40 m × 20 m) each at the fish farm of the Central Institute of Freshwater Aquaculture, Bhubaneswar, India. Of the three treatments evaluated, each with randomly assigned replicated ponds, while fertilizers was the only input in T-1, T-2 was provided with fertilizers and supplementary feed, and T-3 was additionally provided with periphytic substrate at 10% of the pond surface area. The ponds were applied with 10 mg l− 1 chlorine (bleaching powder with 20% available chlorine) after reducing the water to the lowest possible levels. Dead fishes, if any, were removed by repeated netting. The ponds were kept as such for ten days for complete dechlorination (Jena et al., 2002a). Bamboo mats (2 m × 1 m), locally called as ‘tati’, fabricated using trimmed bamboo stripe of 15 mm width and 1.5 mm thickness, were fixed with bamboo poles in T-3, which were driven into the pond bottom so as to keep top edge of the mat at about 15 cm below water surface. To provide substrate area of 10% of pond water surface area, 20 such mats were placed in each replicate pond of T-3 at uniform distance in two rows, keeping 2 m of the peripheral water area free. All the ponds were filled up to 1.5 m depth, with water filtered through fine mesh

Table 1 Water and sediment quality parameters in different treatments T-1

T-2

T-3

Water quality parameters Temperature (°C) pH Dissolved oxygen (mg l− 1) Free carbon dioxide (mg l− 1) Total alkalinity (mg CaCO3 l− 1) Total hardness (mg CaCO3 l− 1) Total ammonia-nitrogen (mg l− 1) Nitrite-nitrogen (mg l− 1) Nitrate-nitrogen (mg l− 1) Phosphate–phosphorus (mg l− 1) Plankton (nos l− 1)

21.0–32.0 (27.3 ± 3.8a) 6.98–8.18 2.3–6.7 (4.2 ± 1.2a) 0–12.0 (6.0 ± 3.5a) 72–108 (89 ± 11a) 60–92 (75 ± 10a) 0.27–0.70 (0.48 ± 0.13b) 0.01–0.07 (0.02 ± 0.01b) 0.34–0.68 (0.45 ± 0.08a) 0.25–0.56 (0.41 ± 0.09a) 11460–15540 (13325 ± 1167b)

21.0–32.0 (27.3 ± 4.0a) 6.90–7.97 2.3–5.6 (3.6 ± 1.1ab) 0–12.0 (7.1 ± 3.2a) 68–92 (77 ± 6b) 56–68 (63 ± 4b) 0.21–0.91 (0.58 ± 0.23a) 0.02–0.10 (0.04 ± 0.02a) 0.30–0.66 (0.41 ± 0.09a) 0.29–0.55 (0.40 ± 0.07a) 15360–24080 (18425 ± 2445a)

21.0–32.0 (27.3 ± 3.7a) 7.00–7.93 2.0–5.4 (3.3 ± 1.0b) 0–12.0 (6.7 ± 3.7a) 68–116 (87 ± 14a) 52–92 (73 ± 11a) 0.25–0.62 (0.41 ± 0.11b) 0.01–0.10 (0.03 ± 0.02ab) 0.30–0.71 (0.41 ± 0.11a) 0.27–0.53 (0.41 ± 0.08a) 15520–23200 (18422 ± 2625a)

Sediment quality parameters pH Organic carbon (% C) Available phosphorus (mg P 100 g− 1) Available nitrogen (mg N 100 g− 1)

6.8–6.9 (6.9 ± 0) 1.2–1.3 (1.3 ± 0.1) 3.3–3.5 (3.4 ± 0.1) 17.9–20.6 (19.3 ± 1.4)

6.7–6.9 (6.7 ± 0.1) 1.1–1.5 (1.4 ± 0.2) 3.0–3.2 (3.1 ± 0.1) 17.3–19.9 (18.9 ± 1.2)

6.8–6.9 (6.8 ± 0) 1.2–1.5 (1.4 ± 0.1) 3.0–3.3 (3.2 ± 0.1) 17.2–20.7 (18.7 ± 1.7)

Values in parentheses expressed as mean ± SD; mean bearing different superscript in a row differ significantly (P b 0.05).

P.K. Sahu et al. / Aquaculture 262 (2007) 333–339 Table 2 Periphyton and benthos population in treatment with provision of substrate Group of periphyton/benthos

Units cm− 2

Bacillariophyta Chlorophyta Cyanophyta Euglenophyta Crustacea Rotifera Total periphyton Benthos

14,168–34,091 (27,066 ± 5541) 8416–18,884 (14,780 ± 3313) 617–5829 (3365 ± 1799) 495–1820 (974 ± 399) 1143–2349 (1608 ± 384) 304–1113 (722 ± 241) 26,799–57,894 (48,516 ± 9202) 12–1204 (349 ± 416)

Figures in parentheses indicate mean ± SD (three depths, two replications and five sampling months, n = 30).

net. Subsequently, the water depth was maintained through fortnight compensation of about 4–6 cm of seepage and evaporation loss. Each pond was fertilized with basal dose of 240 kg raw cowdung (3 t ha1) one week prior to stocking, followed by fortnight application of 500 kg cowdung, 10 kg urea and 15 kg single super phosphate (Jena and Das, 2006). The ponds were applied with lime (CaCO3) at 100 kg ha− 1 month− 1 at monthly intervals after third months of culture for maintaining the water pH within optimum range. Fingerlings of catla, rohu, mrigal and kalbasu obtained from the same farm were stocked at combined density of 7500 fingerlings/ha, keeping the stocking composition as 35, 35, 15 and 15%, respectively. Since both kalbasu and mrigal are bottom feeders, we considered each to constitute 50% of the bottom-feeding component (30%). The initial average weights of fingerlings were 6.1 ± 0.3, 7.1 ± 0.5, 6.2 ± 0.3 and 2.7 ± 0.2 g for catla, rohu, mrigal and kalbasu, respectively. Water and plankton samples were collected fortnightly between 8:00–9:00 a.m., while sediments samples were collected twice, at the beginning and end of culture. The water samples were analyzed for the important parameters (Table 1) following standard methods (APHA, 1998). Sediment samples were analyzed for pH, available nitrogen (De, 1962), available phosphorous (Troug, 1930) and organic carbon (Walkley and Black, 1934). Plankton samples, collected by filtering 50 l of water from each tank through bolting silk net (No. 25, mesh size 64 μ), were preserved in 4% formaldehyde for quantitative analysis. Samples were analyzed by direct census method (Jhingran et al., 1969) using Sedgwick–Rafter counting cell under a binocular microscope (Olympus BX 15). Samplings of periphyton were carried out 30 days after fish stocking and continued on monthly basis. Three mats from each replicate pond were selected at random and periphyton samples were collected from

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upper (0–30 cm), middle (30–65 cm) and lower (65– 100 cm) zones of the mat. At every sampling, while attached periphyton were scraped from 4 cm2 area of each zone of the bamboo mats and preserved in leveled specimen tubes with 5% neutral buffer formalin (NBF) for qualitative and quantitative analysis (Set-I), that from 10 cm2 surface was scraped for estimation of dry matter (DM) and ash-free dry matter (AFDM) (Set-II). The sampled mats were immediately returned to their original position in the pond to prevent them from drying. The periphytic materials collected as Set-I were pooled pond-wise and re-suspended in 50 ml of distilled water followed by addition of 5% NBF as preservative. Periphyton was enumerated using Sedgwick–Rafter counting cell as plankton and identified up to genus level. The samples of Set–II were pooled pond-wise and transferred to pre-weighed and leveled ash-free filter papers (Qualigens 640 d) and then placed in a digital hot air oven at 105 °C for 24 h until obtaining constant weight. After cooling the material overnight in desiccator, the final weight was taken by using an electronic balance (Sartorius BP 110S). The dry matter (DM) was estimated from the weight difference. The crucibles along with their contents were then transferred to a muffle furnace and retained at 550 °C for 4 h. The final weight of the crucible along with the remains was weighed for calculation of ash and ash-free dry matter (AFDM). Fishes were sampled with dragnets of suitable mesh sizes at one-month intervals for assessment of growth and biomass. The mean body weight of each species was recorded from randomly drawn samples of 25 specimens. Table 3 Periphyton biomass (dry matter and ash-free dry matter) and its ash composition obtained from the substrate in T-3 during grow-out carp culture trial Sampling month

Dry matter (g m− 2)

Ash-free dry matter (g m− 2)

Ash (% DM)

February, 2005

36.0–39.3 (37.7 ± 2.3) 32.5–39.9 (36.2 ± 5.3) 25.2–35.0 (30.1 ± 6.9) 17.9–23.3 (20.6 ± 3.8) 24.8–27.8 (26.3 ± 2.1) 17.9–39.9 (30.2 ± 7.4)

15.4–16.8 (16.1 ± 1.0) 14.6–17.1 (15.8 ± 1.8) 13.7–15.4 (14.6 ± 1.2) 7.9–12.5 (10.2 ± 3.2) 13.2–15.8 (14.5 ± 1.9) 7.9–17.1 (14.2 ± 2.7)

58.0–58.9 (58.5 ± 0.6) 56.3–58.5 (57.4 ± 1.5) 46.9–57.5 (52.2 ± 7.5) 49.5–56.8 (53.1 ± 5.1) 41.4–54.8 (48.1 ± 9.5) 41.4–58.9 (53.9 ± 5.9)

March, 2005 April, 2005 May, 2005 June, 2005 ⁎February–June, 2005

Figures in parentheses indicate mean ± SD (three depths, two replications, n = 6); ⁎Range and mean ± SD of five sampling months (n = 10); DM: dry matter.

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Treatments T-2 and T-3 were provided with conventional mixture of groundnut oil cake and rice bran (1:1 w/w) in dough form at 5 and 3% of biomass per day during 1st and 2nd months, respectively, followed by 2% in subsequent months. Quantity of feed was adjusted based on the mean fish biomass of replicate ponds in each treatment, estimated after monthly sampling and considering an assumed survival of 80%. At the end of experiment, the species-wise number and total weight of fish were recorded for each pond for calculation of various yield parameters. The specific growth rate of the fishes was calculated using following formula: Specific growth rate ð%=dayÞ ln final weight−ln initial weight ¼ d100 Days of culture The data were statistically analyzed using PC-SAS programme for Windows, release v6.12 (SAS Institute, Cary, NC, USA) at significance level of 0.05. Analysis of Variance was performed with the General Linear Model procedure. Duncan's Multiple Range Test was performed to compare the water quality and fish yield parameters among the treatments. 3. Results Water pH was significantly higher (P b 0.05) in T-1 over the other two, while dissolved oxygen showed significantly lower values (P b 0.05) in T-3 (Table 1).

The pH gradually reduced in all the treatments during initial three months and remained almost stable subsequently. Dissolved oxygen, on the other hand, showed gradual reduction over the culture period and followed a similar trend in treatments. Water temperature remained within 21.0–32.0 °C, with lower values recorded during the initial two months. While ammonia, in general, showed a gradual increase with progress of culture, nitrite, nitrate and phosphate did not show any specific trend. T-2 with provision of fertilizers and feed recorded significantly higher ammonia and nitrite values (P b 0.05) than the other two treatments. Sediment parameters did not show any marked variations among the treatments (Table 1). The total plankton counts varied within a range of 11,460 and 24,080 units l − 1 , with T-2 and T-3 registering significantly higher (P b 0.05) plankton counts than T-1 (Table 1). The number of periphyton in experimental ponds of T-3 varied within a wide range of 26,799–57,894 units cm− 2 (Table 3). A total of 31 genera of phytoplankton and 4 genera of zooplankton was identified from the periphyton samples, with group dominancy in the order of Bacillariophyta, Chlorophyta, Cyanophyta and Euglenophyta in phytoplankton, and Crustacea and Rotifera in zooplankton (Table 2). Chironomid larva was the only benthos recorded from the periphytic substrate. The DM and AFDM contents of periphyton decreased from second month onwards and the mean values were 30.2 ± 7.4 g m− 2 and 14.2 ± 2.7 g m− 2, respectively (Table 3).

Table 4 Harvesting attributes of carp species with provision of fertilizers, feed and periphytic substrates as different inputs Harvesting details Treatment

Species

Survival (%)

Size (g)

Gross biomass (kg 6 months− 1)

Net biomass (kg ha− 1 6 months− 1)

SGR (% day− 1)

T-1

Catla Rohu Mrigal Kalbasu Total/Avg Catla Rohu Mrigal Kalbasu Total/avg Catla Rohu Mrigal Kalbasu Total/avg

65.7 ± 2.0b 71.9 ± 0.7h 83.9 ± 0.8m 66.7 ± ±3.1r 70.8 ± 0.4y 73.8 ± 1.4a 74.8 ± 1.4gh 89.4 ± 2.4l 84.4 ± 3.1q 78.1 ± 0.8x 72.9 ± 3.4ab 76.9 ± 1.7g 91.7 ± 0.8l 85.6 ± 1.6q 79.0 ± 0.7x

273.5 ± ±2.1b 143.0 ± 1.4i 124.0 ± 5.7m 81.5 ± 2.1s 173.4 ± 2.1z 360.5 ± 0.7a 182.0 ± 7.1h 202.0 ± 12.7l 134.5 ± 3.5r 236.7 ± 0.1y 362.5 ± 7.8a 241.5 ± 7.8g 207.5 ± 3.5l 173.0 ± 2.8q 263.4 ± 1.8x

37.7 ± 1.5 21.6 ± 0.4 9.4 ± 0.5 4.9 ± 0.1 73.6 ± 1.3 55.9 ± 1.1 28.6 ± 0.6 16.2 ± 0.6 10.2 ± 0.1 110.9 ± 1.2 55.4 ± 1.4 39.0 ± 0.4 17.1 ± 0.1 13.3 ± 0.0 124.9 ± 1.9

455.8 ± 18.2 b 251.3 ± 5.2i 110.1 ± 6.4m 58.1 ± 1.3s 875.2 ± 15.6z 682.5 ± 14.1a 338.4 ± 7.4h 196.1 ± 7.5l 124.7 ± 1.4r 1341.7 ± 15.5y 676.9 ± 17.2a 468.7 ± 5.0g 207.0 ± 1.8l 163.5 ± 0.3q 1516.1 ± 24.3x

2.11 ± 0.0b 1.67 ± 0.01I 1.66 ± 0.02m 1.89 ± 0.01s 1.87 ± 0z 2.27 ± 0a 1.80 ± 0.02h 1.94 ± 0.04l 2.17 ± 0.01r 2.04 ± 0y 2.27 ± 0.01a 1.96 ± 0.02g 1.95 ± 0.01l 2.31 ± 0.01q 2.10 ± 0x

T-2

T-3

Mean bearing different superscript for a particular species or total/average in a column differ significantly (P b 0.05); values are expressed as mean ± SD (n = 3). Note: Stocking densities and ratio of carp species were same in treatments, but stocking size of species differed (see text).

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Fig. 1. Species-wise growth of carps in treatments with provision of fertilizers, feed and periphytic substrate as different input during grow-out culture.

Provision of each additional input like feed and periphytic substrate to fertilizers resulted in significantly higher increase in overall net fish biomass, growth and survival (Table 4). The mean overall final weight of carps was the highest in treatment T-3 (263.4 g), followed by T-2 (236.7 g) and T-1 (173.4 g). The growth trends of carps through the culture period are presented in Fig. 1. All four species in T-2 and T-3 recorded significantly higher (P b 0.05) survival, growth, SGR and biomass production than their counterparts in T-1 (Table 4). Further, while in catla and mrigal, no significant difference in all these yield attributes were recorded between T-2 and T-3 (P N 0.05), the values in rohu and kalbasu were significantly higher (P b 0.05) in T-3 than T-2 (Table 4). The FCR in T-2 and T-3 were 1.75 ± 0.02 and 1.77 ± 0.03, respectively with no significant difference (P N 0.05), between the two treatments. 4. Discussion Significant reduction in water pH in T-2 and T-3 compared to T-1 in the present study is attributed to

higher organic load derived from unutilised feed and faecal matter from significantly higher fish biomass in former two treatments (Das et al., 2005). Though initial reduction of water pH was corroborated to mineralization of added organic manures, intermittent liming helped in stabilisation of pH in later part of culture. Decrease in dissolve oxygen with progress of culture in treatments was attributed to the increase in fish biomass (Jena et al., 2001, 2002a,b). Similarly, the significantly higher dissolved oxygen in T-1 compared to other two treatments was obviously due to the presence of significantly less biomass in the former at any point of time. The increased ammonia and nitrite contents with the progress of culture were attributed to the fertilization and gradual accumulation of metabolites and uneaten feed (Jena et al., 2001, 2002a,b). While higher ammonia levels in T-2 are attributable to the above factors, additional uptake of ammonia by periphyton probably led to its reduced level in T-3. However, all the nutrients viz., ammonia, nitrite, nitrate and phosphorus were within the optimum ranges for carps (Banerjea, 1967; Jana and De, 1988; Jena et al., 2002a,b).

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The sediment characteristics in different treatment ponds represented moderate fertility status of the soil and were within optimum range for carp culture (Banerjea, 1967; Jena et al., 2002b). Despite the moderate fertility status, higher plankton levels maintained throughout the culture period denoted benefit of intermittent fertilization. Further, significantly lower plankton level in T-1 was obviously due to its higher utilization by the fish in absence of supplementary feed. The mean periphyton counts of 4.85 × 104 units cm− 2 recorded in the present trial was comparatively lower than the values (1.24 × 106 – 1.46 × 106 units cm− 2) reported by Azim et al. (2001a). Further, the recorded DM of periphytic biomass (30.2 ± 7.4 g m− 2) was lower than that recorded by Azim et al. (2002) from culture pond with rohu and catla, but almost similar to the values in treatment with kalbasu, catla and rohu combination. Lower DM in present study might be attributed to grazing of periphytic assemblage by kalbasu and rohu together, which can also be correlated with the relatively higher growth of these two species in T-3. Further, the estimated AFDM of 14.2 ± 2.7 g m− 2 is comparable to that reported by Keshavanath et al. (2001, 2002) using bagassee, but lower than that of van Dam et al. (2002) using bamboo, kanchi and hizol as periphytic substrates. The higher mean growth of carps (36.4%) and also the species-wise growth of all four species in T-2 compared to those of T-1 complied the established principle of higher weight gain through provision of supplementary feed in the former. Similarly, significantly higher overall mean growth of 11.2% achieved in T-3 compared to that of T-2 indicated additional utilisation of periphyton as natural food in the system, over and above the available plankton. Precisely, the 32.6 and 28.6% higher growth in rohu and kalbasu, respectively, in T-3 compared to T-2 were attributed to grazing of the periphytic material by these two species. Such periphyton grazing (Ramesh et al., 1999; Azim et al., 2002) and higher growth (Wahab et al., 1999a; Azim et al., 2001a, 2002) have been reported earlier in kalbasu and rohu in periphyton-based aquaculture experiments. Though the Substrate Area Index (SAI = area of periphytic substrate/pond water surface area) of only 0.1 was lower in the present study compared to earlier field experiments with SAI more than 0.5 (Azim et al., 2001b, 2002, 2004; Keshavanath et al., 2002), the growth increment of rohu and kalbasu has been substantial. The insignificant growth difference of catla and mrigal between T-2 and T-3 in the present study suggests little or non-exploitation of periphyton by these species, which might be attributed to the low preference and/or difficulty in grazing due to their

upturn and sub-terminal mouth, respectively. However, the marginal weight increase in both catla and mrigal in T-3 might be attributed to the indirect benefit from less competition with rohu for planktonic food (Azim et al., 2004) and prevalence of better water quality and living condition ensured by periphytic substrates, as evident from the significantly low ammonia levels in T-3 compared to T-1 and T-2. The mean SGRs of carps among treatments in present study varied within narrow range of 1.87–2.10% day− 1 and were comparable to 1.57–2.06% day− 1 reported by Azim et al. (2001b). Stocked at equal ratio, performance of kalbasu was lower than that of mrigal in all treatments, probably due to its lower stocking size. However, the higher SGR of the species suggests its growth potential, especially in periphyton based culture system. Significantly lower species-wise survival in T-1 were obviously due to insufficiency of natural food at such higher density of 7500/ha, while provision of supplementary feed led to higher survival in T-2. Additional provision of periphytic substrate further caused a marginal increase in survival in T-3 over T-2, attributed to increased supply of natural food (Wahab et al., 1999a,b; Keshavanath et al., 2001, 2002). Further, among the two bottom dwellers, mrigal showed higher survival over kalbasu in all treatments probably due to its higher stocking size. The FCR of 1.75–1.77 in the present study, calculated based on the supplemented feed, are comparable to that reported in similar six-month carp polyculture experiment of Jena et al. (2002a). Despite the significant difference in net production of treatments T-2 and T-3, their FCR did not differ significantly due to provision of feed based on their standing biomass. Quality and quantity of inputs greatly influence the productivity of aquaculture system. The present study showed significant influence of fertilizers, supplementary feed and periphyton on fish production. This was evident from the 53.3% and 13% higher net yield with additional input of feed in T-2 over T-1 and periphytic substrate in T-3 over T-2, whereas provision of feed and substrate together caused 73.2% higher production in T-3 over T-1. Jena (1998) reported 91% higher fish production using supplementary feed and fertilizers together over use of fertilizer only at 10,000–30,000 ha− 1 stocking densities. Working with Tor khudree and Labeo fimbriatus, Keshavanath et al. (2002) reported 30–59% and 54–87% higher production using only supplementary feed, and combination of feed and periphytic substrate in monoculture system. Low SAI of 0.1 in the present study probably led to such marginal increase in production (13%) compared to higher production enhancement reported by Azim et al. (2004) with 0.5–1.0 SAI.

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