Developmental changes of the digestive capacity and hormones levels in developing embryos and yolk‐sac larvae of tongue sole, Cynoglossus semilaevis

Abstract

Developmental changes in enzymatic activities of alkaline phosphatase (AKP), acid phosphatase (ACP), amylase (AMY), pyruvate kinase (PK), Leucine aminopeptidase N (LAP), Lipase (LIP), Glutamic oxalo acetic transaminase (GOT), Lactate dehydrogenase (LDH), Chymotrypsin (CHY) and Trypsin (TRY) and levels of thyroid hormones and cortisol were measured in developing embryos and yolk-sac larvae of tongue sole, Cynoglossus semilaevis. During embryonic developmental periods, the fastest growth occurred in blastula stage and hatching appeared at 38.8 hours after fertilization (HAF). Besides PK which appeared in cleavage stage onwards, the other enzymes were observed in fertilized egg. Changeable patterns of enzymatic activities presented five types including upward trend for AMY and CHY, M-shaped trend for LIP and PK, V-shaped trend for LAP and GOT, W-shaped trend for LDH and TRY, and an oscillation trend for ACP and AKP. As for hormones, patterns were M-shaped trend for T3, oscillation trend for T4 and downward trend for cortisol. Furthermore, LDH, LIP, PK, TRY, ACP, GOT and T4 showed relatively high levels in blastula stage, which may be an important factor leading to the most rapid growth of embryo. Regression analysis revealed that AMY, GOT and ACP were significantly correlated with embryonic mass, which may provide an effective way to evaluate development of embryos. During yolk-sac larval periods, mouth-opening day appeared at 3 days after hatching (DAH). Besides LAP, GOT, T4 and cortisol which showed downward tendency, the other enzymes and T3 displayed upward tendency and reached the peak at 3 DAH, preparing well for upcoming exogenous digestion.