Diurnal patterns of tryptic enzyme activity under different feeding regimes in gilthead sea bream (Sparus aurata) larvae

• The effect of different feed on diurnal rhythm of tryptic enzyme activity was investigated in sea bream larvae.
• A circadian rhythm in proteolytic digestive capacity was observed in continuously fed (MD) or 3 times batch fed (live feed).
• A limitation in digestive capacity in the afternoon appears, independent of what kind of feeding regime was applied.

Knowledge about the dynamics of the diurnal digestive enzyme capacity during early larval stages of fish is crucial for the determination of appropriate feeding time and frequency. However, there is little data available considering only few species of fish. In this study, several short-term (20 h) diurnal rhythm experiments were conducted under 24 h light conditions to assess the impact of different dietary treatments on the diurnal patterns of tryptic enzyme activity in gilthead sea bream (Sparus aurata) larvae. Four different feeding regimes (group fed with rotifers Brachionus plicatilis (R), with Artemia (A), with rotifers and Artemia (RA) and with MicroDiet (MD)) were assessed at four different age stages (21, 26, 34 and 44 dph). Experimental groups were fed three times a day at 07:15, 14:15 and 22:15, and only the group fed with MD was fed every 15 min with an automatic feeding system. In addition, for each experiment, a subgroup of larvae deprived of food was evaluated as control. Diurnal variation of tryptic activity in fed sea bream larvae groups showed a clear response on the administration of feed with increasing tryptic enzyme activity response after the feeding events. However, the activities in the morning and at noon revealed relatively high levels in comparison to the activity after feeding in the evening. In contrast, tryptic enzyme activity remained significantly lower in larvae deprived of food compared to the fed groups throughout the day. Larvae in groups A and MD at 44 dph showed a similar diurnal pattern in tryptic enzyme activity although group MD was fed continuously. The results suggest that no matter what kind of diet was applied sea bream larvae have a limited digestive capacity at some point in time during the day.Statement of relevanceThis study will help to reduce the cost for fry production.