Effect of age-at-weaning on digestive capacity of white seabream (Diplodus sargus)

White seabream (Diplodus sargus) is today recognized as a potential species for Mediterranean aquaculture. Still, scarce information exists on weaning practices in order to reduce the live food period. This study aims to evaluate the effect of an early weaning on fish larvae digestive enzymes activities. In order to accomplish this, larvae were weaned with an inert diet at 20 days after hatching (DAH) (feeding regime W20) and a control group was weaned at 27 DAH (feeding regime W27). Before weaning, the onset and development of the main digestive enzymes were studied. The pattern of variation of digestive enzymes activities were analyzed at 0, 2, 9, 13 and 20 DAH, and from then on at 0, 1 and 3 weeks after diet introduction; that is, at 20, 27 and 41 days for feeding regime W20, and days 27, 34 and 48 days for feeding regime W27. Trypsin, amylase, lipase, acid protease, alkaline and acid phosphatase, aminopeptidase and leucine-alanine peptidase were analyzed on whole larvae until 20 DAH and on the abdominal cavity and purified brush border during weaning trial period. Until 20 DAH, trypsin, alkaline phosphatase, leucine-alanine, aminopeptidase and acid phosphatase specific activities increased significantly while acid protease, amylase and lipase kept relatively constant. Early-weaned larvae (W20) exhibited a lower growth compared with normally weaned larvae (W27) but the pattern of Relative Growth Rate (RGR) variation was identical for both feeding regimes. Amylase and lipase activities increased swiftly after weaning in both groups as a result of an adaptation to the inert diet composition. During this period acid protease increased as a result of a functional stomach (pepsin activity) rather than inert diet introduction. Results obtained with alkaline phosphatase and aminopeptidase suggested that an early weaning did not affect intestinal maturation. Moreover, results obtained with the brush border could indicate that an early weaning had a positive role in intestinal maturation. Nonetheless, no significant differences were observed on the majority of fish larvae digestive enzymatic activity between treatments 3 weeks after inert diet introduction, and although larvae from W20 feeding regime were more affected initially, they were able to recover to similar levels of activity. This study suggests that an inert diet can be included in the feeding regime of white seabream as early as 20 DAH (360 degree-days). (C) 2009 Elsevier B.V. All rights reserved.