Ontogeny of Expression and Activity of Digestive Enzymes and Establishment of gh/igf1 Axis in the Omnivorous Fish Chelon labrosus

Abstract

Thick-lipped grey mullet (Chelon labrosus) is a candidate for sustainable aquaculture due to its omnivorous/detritivorous feeding habit. This work aimed to evaluate its digestive and growth potentials from larval to early juvenile stages. To attain these objectives the activity of key digestive enzymes was measured from three until 90 days post hatch (dph). Expression of genes involved in digestion of proteins (try2, ctr, pga2, and atp4a), carbohydrates (amy2a), and lipids (cel and pla2g1b), together with two somatotropic factors (gh and igf1) were also quantified. No chymotrypsin or pepsin activities were detected. While specific activity of trypsin and lipase were high during the first 30 dph and declined afterward, amylase activity was low until 57 dph and increased significantly beyond that point. Expression of try2, ctr, amy2a, and cel increased continuously along development, and showed a peak at the end of metamorphosis. Expression of pla2g1b, pga2 and atp4a increased until the middle of metamorphosis and decreased afterwars. Most of these trends contrast the usual patterns in carnivorous species and highlight the transition from larvae, with high protein requirements, to post-larvae/juvenile stages, with omnivorous/detritivorous feeding preferences. Somatotropic genes, gh and igf1, showed approximately inverse expression patterns, suggesting the establishment of the Gh/Igf1 axis from 50 dph.