Co-feeding marine fish larvae with inert and live diets

ELSEVIER

Aquaculture

155 (1997) 183-191

Co-feeding marine fish larvae with inert and live diets 6. Rosenlund

a,*, J. Stoss b, C. Talhot a

Abstract

Combining live feed and manufactured diets (co--feeding) from an early develo;jmen!aI *it;>;gihas been shown to improve growth and survival of marine fish larvae compare-l to the u!:e ~4 live feed only. Co-feeding seems to serve two purposes; it improves and stabilizes the nutr~~:o~~~~ condition of the larvae and it pre-conditions the larvae to accept rhe manufac:nrrci &at why :~;e feed is withdrawn, resulting in a shorter weaning period. Factors affecting :he ;apesri:~! :IIE! utilization of manufactured diets, and the importance of relating ihe tiiTe ~jle~: !‘r,:,+ i :/:‘’ poglossus hippogkwsus), under practical hztch?:~ co3diricti.s ar?, :!c:” .t.c : i ’ : Science B.V. Keywords:

Larval fish: Weaning: Feeding: Manufactured

diets

_.. __.____ _... 1. Introduction

Production of marine fish larvae is dependent on the use of live feeds (alf;ac, I ~:itixs and Artemia) for initial feeding (Halt, 1993; Person Le Kuyit et RI.. I%_<‘:, C‘ ,: ,: $: increases the complexity, difficulty and cost of juvemle fish produ;oon. i+urrl~z;r,~crc. acceptable growth rates cannot be maintained using !ive feed exclusively due to t%: 1:~:. nutrient content and restricted feed intake (Olsen et al., i592). Manufactured &et:, L.m address these problems. However, a lower performance is ~commnnly reporte;: + or: inert diets have been fed to larvae from the on~set of exogenous fe~i::~r~:‘>i’A:\- TT2) ;qr-

* Corresponding

author. Tel.: +47-5180-3X55;

0044.8486/97/$17.00 PIf SOO44-8486(97)001

far:

-I-47-5 1X-1431,

0 19Y7 Elsevier Science 9.V. b.11 rights revmed 16-6

a?-n~:-i!, ?“‘i’??

~‘;.si.xl c.-

184

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to the composition, palatability, or physical characteristics of dry feed (Person Le Ruyet et al., 1993), or an inability to properly digest the feed (Halt, 1993; Kolkovski et al., 1993; Walford and Lam, 1993; Zambonino Infante and Cahu, 1994). The feeding of an inert diet may also decrease water quality if not carefully controlled which may in turn contribute to high mortality and poor growth (Leu et al., 1991). Combined feeding of live and manufactured diets, referred to as co-feeding, from the start of exogenous feeding or from an early larval age, represents an alternative strategy. This has been shown to enhance larval performance beyond that achieved by feeding either types of feeds alone (Kanazawa et al., 1989; Holt, 1993; Leu et al., 1991; Abi-Ayad and Kestemont, 1994), and to permit weaning in a shorter time (Person Le Ruyet et al., 1993). An increased supply of more suitable nutrients is probably the main effect of co-feeding manufactured diets, although this may not apply to microencapsulated diets where the inert coating can be as much as 95% of the dry weight (Lbpez-Alvarado et al., 1994). On a dry weight basis a non-microencapsulated dry feed particle can be 20 times heavier and provide 25 times more gross energy than an enriched Artemia nauplius of similar size (Table 1). There are a number of important issues related to nutrition, fish biology and husbandry which determine the success of co-feeding. There appear to be specific periods during development when fish larvae will eat manufactured diets and this is related to behavioural and physiological capacity (Barnab and Guissi, 1994). However, many farmers start feeding dry feeds from an arbitrary larval age rather than at a measurable developmental stage. For co-feeding to be successful, it is important that the larvae eat dry feed when live feed is also present. FemBndez-Diaz et al. (1994) found that gilthead seabream (Sparus auvuta) larvae previously fed live feeds, would preferentially select live feed during co-feeding. This may reflect a pre-conditioning to the live feed. In a study of white seabass ( Atructuscion nobilis), Dutton (1992) showed that prior experience of a prey type improved feeding success when the same prey was subsequently encountered. This learning process implies that co-feeding will increase the Table 1 Proximate composition (8 of dry weight) and gross energy (J rngmicroparticulate diet (particle size 0.3-0.5 mm)

Protein Fat Carbohydrate Gross energy (J mg- ’ ) ’ Particle dry weight ( wg) Energy/particle (J)

Rotifers ’

Enriched

38.3 18.6 14.2 18.7 0.35 0.007

60.1 14.4 14.1 22.2 1.8-2.5 0.04-0.06

’ dry weight) in typical live feeds and a dry

Artenzia nauplii ’

Ongrown 57.8 14.6 nd 20-22 4 0.08

Artrmia ’

Dry feed d 66.1 19.6 3.9 28.3 16-75 0.5-2. I

a FernBndez-Reiriz et al. (1993). b Mourente and Tocher (1992). ’ Artemia ongrown for 3 days, Reitan et al. (unpublished data), carbohydrate was not determined, but is assumed to be 10% for calculation of gross energy. ’ Experimental diet (Nutreco ARC). Based mainly on fish meal and fish oil. Vitamins and minerals added. ’ The conversion factors used to calculate these values were 23.6, 39.2 and 17. I .I mg- ’ , for protein, fat and carbohydrate, respectively.

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acceptability of dry feed when live feed is withdrawn. In order for larvae to utilize manufactured feed, they must be able to digest and assimilate the nutrients, and co-feeding appears to facilitate these processes (Munilla-Moran et al., 1990; Holt, 1993; Person Le Ruyet et al., 1993). This appears to be due to exogenous enzymes provided by the live feed. Kolkovski et al. (1993) found that addition of exogenous pancreatin improved the digestion of a microparticulate diet in gilthead seabream by 30%. The nutritional content of both live and manufactured diets is also of considerable importance for growth, survival, and the success of weaning (Bromley and Howell, 1983; Person Le Ruyet et al., 1993). Much attention has been paid to the dietary lipid composition due to the essential role of the (n - 3) highly unsaturated fatty acids ((n - 3) HUFAs) and especially of docosahexaenoic acid (DHA), in the nutrition of larval fish (Watanabe, 1993). Much less is known about the requirements of larvae for the other essential nutrients. In this regard, manufactured diets offer considerable scope for dietary manipulation. This paper presents some results from co-feeding experiments with seabass (Dicentrurchus labrux), gilthead seabream (S. aurutu), turbot (Scophthulmus maximus) and Atlantic halibut (Hippoglossus hippoglossus) under practical hatchery conditions. These results are discussed in relation to the ingestion, digestion and nutrient content of manufactured feeds, and to the larval developmental stage when co-feeding can be used successfully.

2. Materials 2. I. Effect

and methods

qf early weaning on growth and suruicul in halibut lun:ae

The experiment was carried out in 350-l tanks at Tinfos Aqua A/S, P)yestranda, Norway, with 140-mg halibut larvae which had been fed with natural zooplankton for approximately 70 days in closed bags placed in the sea (Stolt Sea Farm, Aga, Norway). The tanks were supplied with running seawater (30 ppt salinity at 12 & 2°C) at a rate of 6- 10 1 mini ‘, and exposed to continuous light. The oxygen level was maintained close to saturation. The dry feed groups received feed in surplus to ongrown Artemiu during the first 10 days and during the next 10 days dry feed gradually replaced Artemiu. In the final 20-day period, the dietary treatments consisted of either ongrown Artemiu fed in excess (concentration kept at 100 Artemia 1-l ) or dry feed only (20% of body weight, BW, day- ’ ). Composition of the experimental dry diet is given in Table 1. The stocking density differed between the duplicate tanks within each dietary treatment, but was comparable between treatments. At the end of the trial approximately 60 fish were sampled from each tank, surface moisture removed, and weighed to the nearest mg. Mortalities were removed daily and survival rate was calculated. 2.2. Growth and surcicul in early weaning trials with turbot The experiments were carried out in 350-l tanks at Tinfos Aqua A/S during 1993 and 1995. The tanks were supplied with running sea water (29-32 ppt salinity at

1%

G. Rosenlund et

uI./Aquaculture 155 (1997) 183-191

20.2 i 0.5”C and 20.8 f 0.2”C in 1993 and 1995, respectively) at a rate of 6 1 min-‘, ar:d exposed to continuous light. The oxygen level was maintained close to saturation. ‘The different dietary treatments started on day 21 after hatching and lasted for 15 days. Ali treatments were tested in triplicate with 200 fish per tank initially. For the test grq?s, dry feed (Table 1) gradually replaced Artemia during days 1-7, followed by dry feed oniy during days 8-15 (25% BW day-‘). The control group received ongrown AIK~ZU only during the whole experimental period. In 1993, the fish were fed enriched Arrrr?::tl tbr three days prior to start of the experiment, whereas in 1995 the fish received ~ng::l(~wn Artemia nauplii during this period. The average start weight was 34 mg (H = 4.‘:) in 1993 and 61 mg (n = 60) in 1995. At the end of the trials all fish in each tarlrr were bulk weighed (surface water removed), counted and the average final weights were carculated. Mortalities were removed daily and counted. In the 1995 trial, fish were tiepr1ved of toad overnight and sampled on day 0 (30 fish), day 8 (30 fish tank-‘) and to determine the fatty acid composition in the total lipid ac~:nrJirlg to the method described by Lie and Lambertsen (1991). 2 .J Co-feeding

trials with seabass and gilthead seabream

‘l’hz trials were carried out at the Danish Institute for Fisheries Technology and Aquactiltlnc (Wirtihals, Denmark). Triplicate 330-l tanks supplied with recirculated wstz wz-P stocked with approximately 4000 larvae per tank. The water temperature and \a’:;nlty were 21 5 .k O.il”C and 32 5 2 ppt and 23.3 _t 0.4”C and 33 + 1 ppt for seabass arid >c::brYarr!7 respectively. Oxygen content in the outlet water was maintained above 07% Laturation. Daily renewal of water was approximately 15%. Prior to the experiments :hc fish were fed rotifers, Artemia nauplii and thereafter enriched Artemia. For 6 fi;lvs from 3! and 34 days post-hatch for seabass and seabream, respectively, three tanks r&i~d a supplement of dry feed (approximately 10% BW day-‘) together with the (;iII r..;.!ic)n of live feed while the other three tanks were fed only the full ration of /r r,+t’z+l C~.lri?g tlfie period 37--48 and 40-5 1 days post-hatch for seabass and seabream, r~n~ctively. dry food (Table 1) gradually replaced live feed. The daily amount of if rzrnic! was reduced from 1.O to 0.3 million and from 1.6 to 0.2 million per 1000 fish for seabass and seabream respectively, and the daily ration of dry feed for both species was increased from 12 to 20% BW. Final body weight was determined in individual fish f > 100 tank- ’ > to the nearest 0.1 mg at 58 and 61 days after hatching for seabass and resgectively. !~ilbtY~~,

time period (days) v+llere \A/, , are the Initial and final weights, respectively.

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The effect of dietary treatments on final body weight was analyzed by ANOVA and t-test. A probability level of P < 0.05 was used to judge whether any effects were significant. 3. Results and discussion The results of the co-feeding experiment with halibut larvae are shown in Table 2. No significant difference was found between mean final body weight within each dietary treatment due to the effect of stocking density. However, using pooled data from the two density treatments within each dietary treatment (n = 117 and 120, respectively), there was a highly significant difference (P < 0.001) between the mean final body weights of the co-fed group (397 _t 338 mg) compared to the group fed only live feed (276 + 155 mg). The SGR for the whole experimental period was 2.6 and 1.7% day-’ for the co-fed and the Artemia groups, respectively. At the end of the trial, the largest individual in the group fed only Artemiu weighed 620 mg compared with 1940 mg in the co-fed group. Approximately 50% of the co-fed fish survived whereas only around 25% of the halibut larvae fed only Artemia survived (Table 2). The higher mortality and lower growth compared to the co-fed treatments suggested that halibut maintained on Artemiu were malnourished although they were fed in excess. Similarly, Segner and Witt (1990) found morphological alterations associated with malnutrition in turbot larvae fed live feeds (rotifers and thereafter enriched Artemia) for 21 days. In the halibut trial described in this paper, the colour of the stomach contents indicated that ingestion of dry feed started around the time when Artemiu were gradually withdrawn (from day 11 onwards). This observation, together with the improved growth and survival, would suggest that halibut larvae will eat dry feed in the presence of Artemiu, and utilize dry feed from an earlier developmental stage (140 mg body weight) than is commonly practised in commercial hatcheries. Halibut juveniles are normally not weaned to manufactured feed until metamorphosis, i.e., a size of approximately 250 mg (Berg, 1995).

Table 2 Effect of early weaning on growth and survival in halibut larvae Tank Food Stocking density

Ll Live High

L2 Live Low

Dl Live + Dry High

D2 Live + Dry Low

237 256fl59” 57 50-620 29.2

Dry feed + 100% Artemia Dry feed +reduced Artemia Dry feed only 440 262 372+ 327 b 423+350 b 60 60 20- 1940 loo-1630 42.0 59.1

Feeding-regime

Day l-10 Day 1 l-20 Day 2 l-40 Stocking density (# tank-’ ) Final weight (Mean i SD mg) n

Artemia Artemia 459 295*150” 60

1 lo-610 24.1

Range (mg) Survival (7~) Means with a different

Artemia

superscript

letter are significantly

different (P < 0.05).

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Table 3 Growth and survival in early weaning Diet 1993 Dry feed Ongrown I995 Dry feed Ongrown

155 (1997) 183-191

trials with turbot from different periods

Final weight (mg)

SGR (% day-‘)

Mortality (7~)

Arfemirr

271t18” 354+21

13.8 15.6

5.8 5 0.6 1.3+0.8

Arremia

384*8 368+ 19

12.3 12.0

1.0+0.5 1.0+0.5

b

Results are expressed as mean ( f SD) of triplicate tanks. Initial average weight was 34 and 61 mg in 1993 and 1995, respectively. Means with a different superscript letter within the same column and trial, are significantly different (P < 0.05).

The results of the turbot trials suggest that within a species, larval weight rather than larval age is a better indicator of the physiological status of the larvae (Table 3). The main difference between the trials was the initial body weight (34 mg in 1993 and 61 mg in 1995). In the 1993 trial, the co-fed populations showed a significantly lower final body weight compared to the larvae fed only Artemia (P < 0.01) and a somewhat higher mortality. However, the co-fed group in 1993 grew at 13.8% day-’ which was comparable with the rate observed in 1995 (12.3% day-‘). In the 1995 trial, the mean body weight of the co-fed fish was 384 + 8 mg compared to 368 _t 19 mg in the larvae fed only Artemia. Although final weights were not significantly different, these results show that turbot can be grown successfully (SGR > 12% day-’ > from 21 days after hatching by co-feeding at a body weight between 35 to 60 mg. The gradual shift found in the larval fatty acid composition from one that was similar to Artemia to one that was similar to the fatty acid composition of the dry feed (Table 4) shows that the dry diet is ingested, digested and assimilated even when Artemia are present. The DHA level in

Table 4 Fatty acid composition (% of total lipid) of ongrown Arremia and a dry diet used in weaning trials with turbot, and the effect of co-feeding on the lipid composition and the DHA/EPA ratio in turbot Fatty acids

Ongrown

Saturates Monoenes Sum n-3 Sum 11-6 DHA EPA ’ DHA/EPA

17.7 44.9 29.8 4.3 7.0 10.2 0.7

Arremia

Dry feed a

28.0 27.3 31.4 10.4 16.3 8.3 2.0

Turbot Day 0

Day 8 h

Day 15 b

21.6 36.5 30.8 6.1 5.3 13.0 0.4

24.3 f 0.2 25.2 f 0.6 34.5 f 0.5 11.6*0.2 16.5 *0.5 10.3 50.2 1.6

25.OkO.3 20.4 f 0.5 36.0 + 0.4 14.1 50.5 20.8kO.l 8.5 f0.2 2.5

a The dry feed had a similar gross composition to that given in Table 1, but 70% of the fish oil (7% DHA) was replaced by an oil containing 27% DHA (Pronova, Sandetjord, Norway). ’ Day 8: co-fed dry feed for 7 days; Day 15: only dry feed from day 8. Mean (*SD) of triplicate samples. ’ Eicosapentaenoic acid.

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Table 5 Effect of supplementing live feed with a dry microparticulate diet for 6 days prior to the start of weaning growth and survival in seabass (D. lahraw) and gilthead seabream (S. aurata). Mean values (*SD) triplicate tanks at the end and of individual fish at the start of the experiments Group

Dry feed introduced

at:

Final wet weight (mg)

Mortality (7~)

10.8&4.1 nd a

251*23 234*5

10.5* 1.4 11.6* 1.2

nd a 17.4i7.6

177*39 152*35

6.1 + 1.3 7.4 * 1.8

Age (days)

Wet weight (mg)

31 37

34 40

on of

BUSS

Supplemented Control Bream

Supplemented Control a Not determined.

the lipid of larvae fed only Artemia was lower than in the Artemia (day 0, Table 4). This is probably due to some breakdown of DHA in the Artemia before it is eaten (Danielsen et al., 1995; Evjemo et al., 1997). However, co-feeding quickly increased the DHA-level in the larval lipid. A rapid and selective incorporation of DHA into brain phosphoglycerides has been demonstrated in turbot and gilthead seabream larvae when Artemia was changed to a dry diet (Mourente and Tocher, 1992, 1993). Dutton (1992) found that feeding success in white seabass (A. nobilis) offered different zooplankton increased if the larvae had previously experienced the prey type. The effect was attributed to learning rather than feed particle size. Whether such a prior-exposure mechanism might work with dry feeds is still unknown. However, the trials with seabass and gilthead seabream larvae, where dry feed was offered as a supplement to a full ration of Artemia for six days prior to the start of weaning (Table 51, suggests that this may be the case. Although not significant at P < 0.05, both seabass and gilthead seabream fed dry feed as a supplement prior to weaning showed higher mean final body weights compared to fish which had been fed only Artemia prior to weaning. This may indicate either that the larvae ingested dry feed during the 6-day supplementation period (effectively increasing the co-feeding period by 6 days), or that this prior exposure had pre-conditioned the larvae to accept dry feed when the supply of Artemia was reduced during the subsequent 12-day weaning period. Person Le Ruyet et al. (1993) stated that the minimum weight for successful weaning of seabass by a direct switch to a manufactured diet is 20 mg. The results in Table 5, however, suggest that seabass of around 10 mg body weight can utilize manufactured diets if co-feeding regimes are used, and attain growth rates in excess of 10% day-‘.

4. Concluding

remarks

As reported in other studies, the results described in this paper demonstrate that co-feeding regimes can improve growth and survival of marine fish larvae. No common larval developmental stage has been identified which is capable of proper ingestion and

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digestion of manufactured diets. Larval weight appears to be a better indicator of larval developmental stage than age, and this measure would make it easier to compare results from different trials. Further studies are required where growth and survival are correlated with functional morphological changes in the larvae in response to different dietary regimes. Such studies could include electron microscopic examination of the gut and other organs associated with the nutritional status of the larva (Segner and Witt, 1990; Kjorsvik et al., 1991; Walford and Lam, 1993; Abi-Ayad and Kestemont, 1994) and measurements of digestive enzyme activity (Walford and Lam, 1993; Cahu and Zambonino Infante, 1994). Co-feeding improves larval nutrition and may pre-condition the larvae to more readily accept the manufactured diet when live feed is withdrawn. In particular, co-feeding can solve the problem of inadequate nutrient supply encountered when the number of live prey required for maximum growth exceeds the maximum ingestion rate of the larvae. A large variation in body size was seen in co-fed larvae and higher maximum weights were generally observed compared to fish fed live feed. This may be in part related to the generally better survival as a result of greater trophic diversity. Technical rather than nutritional constraints are perhaps the main limitation to the early introduction of dry feed in large-scale production systems. There is a major risk of reduced water quality when using dry feeds which in turn leads to loss of appetite and subsequently to larval mortality. As a result, problems with tank management often obscure the effects of dietary composition. Husbandry should be an integrated part in future research aiming to develop more optimal feeds for marine fish larvae. Better knowledge regarding feeding behaviour for the different species cultivated, as well as technical solutions related to feed distribution, are required. Considerable progress has been made in recent years in reducing the dependence on live feeds (dry feed already replaces about 70% of the live feed in practical production of ayu Plecoglossus altivelis (Leu et al., 1991)), and it is likely that this trend will continue. Acknowledgements Parts of this work were carried out in a project jointly sponsored by The Research Council of Norway (Grant BF 1050481, Stolt Sea Farm A.S. and T. Skretting A/S. Contributions from the project group are gratefully acknowledged. Thanks are also due to the staff at DIFTA for conducting the seabass and seabream trials, and especially to Per Bovbjerg. References Abi-Ayad, A., Kestemont, P., 1994. Comparison of the nutritional status of goldfish (Carassius auratus) larvae fed with live, mixed or dry diet. Aquaculture 128, 163-176. Barnabe, G., Guissi, A., 1994. Adaptations of the feeding behaviour of larvae of the sea bass, Dicentrarchus labrax CL.), to an alternating live-food/compound-food feeding regime. Aquacult. Fish. Man. 25, 537-546. Berg, L., 1995. Commercial feasibility of semi-extensive larviculture of Atlantic halibut (Hippoglossus hippoglossus L.). In: Lavens, P., Jaspers, E., Roelants, I. (Eds.), Larvi ‘95-Fish and Shellfish Symposium, Gent, Belgium. Europ. Aquacult. Sot., Spec. Publ. 24, 359.

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