Solubility and peptide profile affect the utilization of dietary protein by common carp (Cyprinus carpio) during early larval stages

The present work aimed at evaluating whether solubility and peptide profile of dietary protein can affect survival and growth performance of common carp during early stages of life. Water-insoluble casein and two forms of soluble casein (non-hydrolysed and hydrolysed) were used as protein sources at different proportions in the experimental diets for first-feeding carp larvae. When provided as the only protein source water-insoluble casein led to high mortality and depressed growth after 21 days. The partial or total substitution of water-insoluble casein by soluble non-hydrolysed casein effectively improved survival and enhanced growth of larvae. An optimum level of soluble non-hydrolysed protein was found at 25% of total protein. The addition of some hydrolysed casein (25% of soluble protein) further improved results. However, high dietary levels of hydrolysed casein led to negative effects on larval performance, which would be related with a surplus of di-/tripeptides or/ and amino acids. Protein solubility appears to have only a temporary effect on larval performance, probably related with the ontogeny of the digestive tract, since about 2 weeks after the onset of exogenous feeding larvae became able to use efficiently water-insoluble protein. Results also suggest the need for a balance in the peptide profile to optimise the utilization of dietary protein by fish larvae. (C) 2004 Elsevier B.V. All rights reserved.