Relationship between body mass and activities of digestive enzymes and immune-related enzymes of juvenile yellowfin tuna (Thunnus albacares)

In order to accumulate the land-based recirculating aquaculture basic data of juvenile yellowfin tuna (Thunnus albacares), we studied the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), amylase, lipase and protease in the serum, muscle tissue, liver, stomach, intestine and other tissues of the juveniles of different body mass. The ACP activity showed a descending order of intestine>muscle>liver>serum, while the AKP activity showed a descending order of intestine>liver>muscle>serum. With the increase of body mass, there was little difference in the ACP activity in muscle, intestine and liver, while the AKP activity in liver increased gradually, and there was significant difference between the two adjacent groups (P<0.05). In general, the digestive enzyme activity of the larvae was stable, without significant difference between the groups (P>0.05). Only when the body mass reached 1 000 g, the intestinal trypsin activity decreased significantly (P<0.05), and then floated in a small range, without significant difference between the groups (P<0.05). In conclusion, the ACP and AKP activities are high and stable in the tissues of juvenile T. albacares, which ensures stable functions for the decomposition, absorption and reuse of phosphorus (P) and immunity to external substances; during the breeding period of T. albacares, the nutritional demand is stable and the protein demand is strong.