Comparative study on early digestive enzyme activity and expression in red sea bream (Pagrus major) fed on live feed and micro-diet

Abstract

The use of live feed to meet larval nutritional requirements has caused a bottleneck in marine fish larviculture whilst the use of micro-diets has had limited success in completely replacing live feeds. In this study, the variations in enzyme activity and its related gene expressions during early ontogenetic development of red sea bream (Pagrus major) were investigated. The experiment included four treatments: (i) using live feed (enriched L-type rotifers of the Brachionus plicatilis sp. complex) until 15 days after hatching (DAH) and gradually switching to Artemia; (ii) using micro-diet only; (iii) co-feeding diet (using both live feed and micro-diet) and, (iv) starvation (no food supplied). This study lasted 40 days and the activity and expression of digestive enzymes (trypsin (try), chymotrypsin (ctrb), pepsin (pep), amylase (amy2α), pancreatic lipase (pl), expression of energy metabolism (ATP synthase (atp), cytochrome-c-oxidase (cox1), cholecystokinin (cck) and growth (insulin like growth factor 1 (igf1)) were linked to larval biometrics. After 40 DAH, no significant difference was observed in growth (igf1), energy metabolism (cox1, atp) and survival rate between live feed and co-feeding diet treatments. However, there were significantly higher differences observed when these were compared to the starvation and micro-diet only treatments. The pancreatic enzymes and cck were regulated by dietary compositions and detectable from hatching and fluctuated throughout larval ontogeny. While pep was initially observed only after 15 DAH. Limits of larval survival and low enzyme activity were observed when the larvae were subjected to starvation for 10 days and were able to adapt to micro-diet only after 15 DAH accompanied with a 5-day co-feeding transitionary period.