Effects of vitamin A on growth, serum anti-bacterial activity and transaminase activities in the juvenile Japanese flounder, Paralichthys olivaceus

The present study examined the effects of dietary vitamin A (vitA) deficiency and excess on growth, serum anti-bacterial activity and serum enzyme activities of juvenile Japanese flounder, Paralichthys olivaceus. Three semi-purified diets containing 0, 10,000 and 25,000 International Units of vitA per kg of diet (IU vitA/kg) were fed to juvenile Japanese flounder (initial weight 1.59 g) for 120 days. At the end of the feeding trial, blood samples were taken from the fish for haematocrit, serum biochemical analysis and serum anti-bacterial activity. Growth performance, in terms of weight gain and specific growth rate, was improved significantly (P < 0.05) with the addition of vitA to the diet. Total retinol contents in the liver increased with increasing dietary vitA levels. Haematocrit values did not show significant difference among the groups, but the values tended to increase with increasing dietary vitA levels. Serum total protein and albumin contents, and glutamyl oxaloacetic transaminase (GOT) activity tended to be lower in fish fed with 10,000 IU vitA/kg but significant difference was not observed among the groups. Serum total bilirubin content was significantly higher in treatment with no vitA than the other treatments. Glutamyl pyruvic transaminase (GPT) activity was significantly higher in the fish fed 25,000 IU vitA/kg than the other two groups. Serum anti-bacterial activity was significantly higher in the groups fed with 10,000 and 25,000 IU vitA/kg than that of the fish fed with 0 IU vitA/kg. These data suggest that dietary vitA significantly improved the growth performance and anti-bacterial activity of juvenile Japanese flounder. The tendency observed of high values in the blood serum parameters of the fish the diets of 0 and 25,000 IU vitA/kg after 120 days, suggests some negative effect on the liver (the main vitA storage site).