Ontogeny and diurnal patterns of molecular gene expression and activity of digestive enzymes in developing greater amberjack

The greater amberjack, Seriola dumerili, is a fast-growing pelagic teleost with great interest for the diversification of farmed marine fish species in the Mediterranean region. Aiming to advance the optimization of feeding during the early stage of this species, this study examines the ontogeny of digestive function using molecular and biochemical approaches. Gene expression of digestive enzyme precursors and the enzymatic activity have been determined during the first 51 days post hatching (dph) and during the diurnal period of 19 dph larvae reared in semi-intensive conditions. The expression of pancreatic proteases precursors (try3, ctra and ctrb1) increased from first-feeding, while gastric chitinase (chia1), gastric protease (pga3) and proton pump (atp4a2) after 10 dph. The expression of pancreatic lipases (cel1, cel2 and cel3) peaked between 6 and 10 dph, phospholipase A2 (pla2g1b) rose only after 25 dph, while α-amylase (amy2a) increased mainly from 20 dph. The trypsin activity was more evident from first-feeding to 25 dph and chymotrypsin activity from this day onwards. Acidic chitinase and pepsin activity appeared, respectively, at 16 and 30. The activity of 7C-like lipase was evident from first-feeding but as 4C-like lipase significantly increased from 15 dph, while amylase peaked from 6 to 22 dph. Aminopeptidase and alkaline phosphatase activities started at 20 dph indicating the functional maturation of brush border of the enterocytes. The daily pattern analysis showed a food anticipatory strategy in the expression of proteases related genes. Lipases activity was more evident during the morning hours, followed by amylase, and by alkaline proteases in the afternoon. Results, also, suggested an alternation in the activity of chymotrypsin and trypsin. These ontogenetic patterns are concordant with a carnivorous marine teleost.