Biochemical composition and activities of digestive and antioxidant enzymes during the egg and yolk‐sac larval development of the cobia ( Rachycentron canadum )

Abstract

Cobia Rachycentron canadum is an economically important fish and is cultured throughout southern China and other part of the world. However, the knowledge of metabolism and nutritional requirements of cobia embryos remains limited. This study investigated changes of the biochemical composition, as well as the activities of related digestive and antioxidant enzymes during the development of both eggs and yolk-sac larvae of the cobia (Rachycentron canadum). The results showed that egg mass at the fertilized stage increased gradually to the blastula stage and showed a significant increase at the segmentation stage and a significant decrease at the larval period. The main components of embryos and larvae were carbohydrates, lipids and proteins. Protein and lipid contents decreased at the blastula stage, increased significantly at the segmentation stage and then decreased thereafter. Carbohydrate contents decreased significantly during the development. Enzymatic activities showed a progressive increase from the embryo to the yolk-sac larval stage. The activities of pepsin and trypsin increased significantly during the development. Amylase activity remained low before the blastula stage and increased rapidly thereafter. Lipase showed an ‘increase–stable–increase’ tendency. Changes of digestive enzyme activities indicated the dynamics of the biochemical composition. Activities of glutathione peroxidase, catalase and superoxide dismutase significantly increased during embryonic and yolk-sac stages, and malondialdehyde contents followed the same trend. The results of the current research provide vital information to enhance yolk exploitation with a specific focus on organogenesis. Moreover, considerable knowledge on the embryonic development of the cobia is presented.