Effects of hydrolysed protein in weaning diets for Atlantic cod (Gadus morhua L.) and Atlantic halibut (Hippoglossus hippoglossus L.

No abstract

In this study Atlantic halibut (Hippoglossus hippoglossus L.) larvae (0.12 + 0.04 g) were, from day 40 post first feeding, offered six diets in which 10% or 30% of the dietary protein was hydrolysed with (a) pepsin (P), (b) pepsin trypsin (PT) or (c) pepsin trypsin chymotrypsin (PTC). In addition, a diet without hydrolysed protein was offered, and enriched Artemia was fed as control. The amount of soluble protein increased progressively with the enzyme treatments P, PT and PTC and with higher inclusion levels of hydrolysed protein. Survival was highest among the larvae offered Artemia (83 + 0%) or the diet 10P (10% pepsin hydrolysed protein; 67 + 4%). The diet 10P supported survival significantly better than the more hydrolysed diets 10PTC, 30P, 30PT and 30PTC, but not significantly better than the non-hydrolysed diet and 10PT. Specific growth rate (SGR) was 1.76 + 0.20 in average for all groups of larvae and was not significantly affected by the diets. Still, the larvae offered pepsin hydrolysed diets tended to have better growth (2.10 + 0.05 SGR; P <0.06) than the larvae offered the other hydrolysed diets. The larvae offered the formulated diets did not differ in chemical composition. Ã 0-diet: non-hydrolysed diet; 10P, and 30P: 10% and 30%, respectively, of the dietary protein was hydrolysed with pepsin; 10PT and 30PT:10% and 30%, respectively, of the dietary protein was hydrolysed with pepsin and trypsin; 10PTC and 30PTC: 10% and 30%, respectively, of the dietary protein was hydrolysed with pepsin, trypsin and chymotrypsin. ²Fish meal extract. See Material and methods and Sola et al. except for a-tocopheryl absorbate supplemented at 200 and ascorbyl palmitate at 400 mg kg À1 . Aquaculture Research, 2002, 33, 311±321 Atlantic halibut larvae fed predigested protein A Kva Êle et al.

Atlantic halibut (Hippoglossus hippoglossus) achieve a mature gastrointestinal tract approximately 2 months after first feeding (12 °C). The immature digestion may be the reason that compound diets fail to sustain growth and survival in first feeding halibut larvae and in larvae of other marine fish species. On the other hand, larvae fed with live feeds are capable of extraction of sufficient quantities of nutrients to sustain high growth rates. A lower availability of the protein in formulated diets compared with live prey is considered to be an important reason for the low performance of formulated diets. One approach to increase dietary protein availability is supplementation of pre‐digested proteins. Experiments using tube fed individual larvae show that halibut larvae are able to utilize hydrolysed protein more efficiently than intact protein. However, Atlantic halibut in culture did not respond well to dietary supplementation of hydrolysed protein, in contrast to some other species. One reason may be extensive leaching of pre‐hydrolysed proteins from the microparticulate feed. Atlantic halibut are slow feeders and may thus suffer more from nutrient leaching than species eating more rapidly. Feed formulation techniques affect dietary protein leaching, and in this paper, different techniques and their impact on feed properties are described. Microbound diets are most widely used in larval rearing, but show high rates of nutrient leaching. Lipid‐based capsules seem to have the best potential to prevent leaching, however, they are not able to deliver a complete diet. The high need for improvements in larval feed formulation techniques are clearly stated, and some suggestions are given. Among these are production of complex particles, where small lipid‐based capsules or liposomes containing the low molecular weight water‐soluble nutrients are embedded. In such feed particles the water‐soluble molecules are protected from leaching. Techniques for delivery of water‐soluble nutrients that are needed in large quantities, i.e. free amino acids or hydrolysed and water‐soluble protein, remain to be developed.

Predigested dietary protein may enhance the utilisation of formulated diets at weaning, and also stimulate intestinal maturation. In this study, Atlantic cod (Gadus morhua L.; 41 days post hatch (dph)) and Atlantic halibut (Hippoglossus hippoglossus L.; 63 days post first feeding (dpff)) were weaned onto diets with graded levels of where varying parts of the protein was substituted with pepsin hydrolysed protein, exchanged with dietary protein. By increasing dietary content of hydrolysed protein from none to 40 %, cod increased the rate of survival from 7±1 % to 18±2 % (82 dph; Regression, P=4*10 -7 ). In halibut, the survival rate decreased from 57±9 % to 22±7 % as the content of hydrolysed protein increased from none to 45 % (119 dpff; Regression, P=8*10 -5 ).Growth was not affected in any of the species. A 3-fold higher specific activity of leucine aminopeptidase (LAP) in cod was found in the groups fed 20 and 30 % hydrolysed protein than in the group fed non-hydrolysed protein (82 dph; ANOVA, P<0.05), indicating a more mature intestine in the former groups. In halibut, specific activity of alkaline phosphatase (AP) was 3-6-fold higher in the groups receiving nonand 15 % hydrolysed protein than in the groups receiving 30 and 45 % hydrolysed protein (91+119 dpff; ANOVA, P<0.05). The lower preference optimal level offor hydrolysed protein in halibut than in cod is suggested to mainly be caused bydue to a slower feeding habit practice in halibut which allow more extensive nutrient leaching before ingestion.3