Dourado (Salminus brasiliensis) larviculture: Weaning and ontogenetic development of digestive proteinases

This study examines the optimal weaning period in rearing larval dourado. This aim is achieved by comparing a series of differential weaning schedules, and by measuring the ontogeny of proteinase activities. Weaning from live food (curimba, Prochilodus lineatus, larvae) was carried out at the third, fifth or seventh day AH by gradual or total transition to formulated feed. Live food was either kept for two days after feeding the test diet (GW) or removed at the same day (TW). Acceptance of test diet started at the fifth day after hatching (AH) and larvae total length was higher (P < 0.05) when feed transition occurred at the third (TW) (20.93 ± 1.33 mm, mean ± SEM) or seventh day (GW) AH (20.41 ± 0.80 mm); however, higher (P < 0.05) wet weight was observed in larvae submitted to feed transition at the third (TW) (0.067 ± 0.014 g) or seventh day (GW) AH (0.078 ± 0.009 g). Total length and wet weight were not affected by the form of alimentary transition (P > 0.05). Survival was significantly lower (P < 0.05) when weaning occurred at the third or fifth day AH when compared to weaning at the seventh day AH. Additionally, survival was superior when transition to formulated feed was gradual. The ontogenetic development of proteinases was measured in the larval gut after hatching by sampling every 12 h AH, during seven days. Acid protease activity (0.0004 ± 0.0 U mg− 1 protein, mean ± SD) was detected at the third day AH and increased subsequently until the seventh day AH (7T), indicating stomach functionality at this time. Intestine proteinases activities (trypsin and chymotrypsin, 0.088 ± 0.0 and 0.018 ± 0.0 U mg− 1 protein, respectively) were detected as early as 12 h AH, before the onset of exogenous feeding. Digestive enzymatic contribution of live food was not clearly shown. Our findings corroborate the hypothesis that fish larvae will accept dry feed only when it is physiologically able to digest it, which happens when acid protease activity is detected, indicating stomach functionality. Our findings also demonstrate the importance of live food soon after hatching for dourado larvae and suggest that formulated feed could be offered, in a gradual form, as early as at the fifth day AH.