Effects of salinity on digestive physiology during early ontogeny in newly hatched larvae of European sea bass (D. labrax)

In this study, the absorption dynamics of endogen food reserves and also specific activities of main pancreatic and intestinal enzymes were investigated in three different salinities (natural sea water, lower salinities as 30 and 25‰) during early ontogeny in larvae of sea bass, Dicentrarchus labrax, until mouth opening. Among experimental groups, mouth and anus were completely opened in larvae and also although yolk sac was nearly absorbed in whole larvae, oil globule was not fully depleted at the end of the 120th h after Hatching (HAH). In all experimental groups, trypsin specific activity rapidly rose up during the first 48 HAH then decreased. Also, this activity increased to until end of the experiment. Lipase specific activity slowly increased during the first 48 HAH then rose up to 120 HAH. Amylase specific activity was almost stationary during the first 48 HAH and then gradually increased to the end of the experiment. From this time to the end of the experiment this activity slowly declined. For intestinal enzymes, Alkaline Phosphatase (AP) and leu-ala peptidase activity presented converse profile among the experimental groups. The specific activity of AP demonstrated quite similar pattern for trypsin during the experiment. For leu-ala peptidase activity, opposite pattern was observed for AP activity during the first 24 h, specific activity was relatively higher but after then, it slowly decreased concurrently in all experimental groups. As a result of this study, obtained results clearly summarized that significant differences were recorded in all experimental groups, however, the lower salinity levels (25 and 30‰) in experimental groups demonstrated relatively significant and higher results in terms of endogen reserves absorption, larval growth performance, survival rate and digestive enzyme activities compared to natural sea water experimental group (p<0.05). © Medwell Journals, 2014