Effect of vitamin E and C dietary supplementation on some immune parameters of gilthead seabream (Sparus aurata) juveniles subjected to crowding stress

High stocking density is an aquaculture-related situation which causes crowding stress in fish and potentially affecting the immune system. Protection against disease can he induced through immunostimulation, enhancing defence mechanisms. Vitamins C and E are among the most important nutrients influencing the immune system, although the effect of these vitamins in the amelioration of stress in fish has not been studied in detail. An experiment was carried out to study the effect dietary supplementation of vitamin C or vitamin E on the immune system of fish under a crowding stress situation in a commercial farm. A commercial diet for this species was supplemented with vitamin C or vitamin E and these diets were assayed at high stocking density (over 40 kg m(-3)) and the results were compared with those from fish fed the commercial diet and held at farm conditions (20 kg m(-3)). Some biological and immunological parameters were studied at the end of the experimental period. Fish held at high stocking density showed lower final weight than fish held at lower stocking density. These also showed higher plasma cortisol levels (over 6 ng cortisol ml(-1) plasma for all the diets assayed) than those fish held at lower density (1.13 ng cortisol mi(-1) plasma). High stocking density produced higher serum lysozyme activity values in fish fed the commercial diet compared with those fish held at lower density (67.49 and 36.84 units ml(-1), respectively). This effect was not observed in fish held at high stocking density but fed vitamin C and vitamin E supplemented diets (lysozyme activity: 21.97 and 19.71 units mi(-1), respectively). High stocking density also appeared to decrease serum alternative complement activity. Ln those fish fed the vitamin E supplemented diet, levels were similar to fish held at low stocking density, suggesting the role of this vitamin in this defense mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.