GROWTH, MORTALITY, TISSUE HISTOPATHOLOGY AND FATTY-ACID COMPOSITIONS,EICOSANOID PRODUCTION AND RESPONSE TO STRESS, IN JUVENILE TURBOT FED DIETS RICH IN GAMMA-LINOLENIC ACID IN COMBINATION WITH EICOSAPENTAENOIC ACID OR DOCOSAHEXAENOIC ACID

Three diets containing either borage oil (BO) and southern hemisphere fish oil Marinol (MO), or BO and tuna orbital oil (TO), or a northern hemisphere fish oil (FO) were fed to duplicate groups of turbot (Scoph thalmus maximus) of initial mean weight 1.2 g for a period of 12 weeks . The BO/MO and BO/TO diets were enriched in gamma-linolenic (18:3n-6, GLA) and eicosapentaenoic (20:5n-3, EPA) acids, and GLA and docosahex aenoic acid (22:6n-3, DHA), respectively. No differences were observed in final weights or growth rates, either between duplicate tanks or b etween dietary treatments. Half of the FO-fed fish sampled showed a hi stopathological lesion indicative of lipoid liver degeneration while t he other treatments only showed a slight incidence of the same patholo gy. The fatty acid compositions of carcass and tissues broadly reflect ed the dietary input. In general, fish fed the BO/MO diet had increase d levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:5n-3, but a lower level o f 22:6n-3, compared to fish fed FO. In fish fed the BO/TO diet, levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:4n-6 were increased while levels of 20:5n-3 and 22:5n-3 were reduced, compared to fish fed FO. Concentr ations of thromboxanes B (TXB) and leukotrienes B (LTB), derived from 20:4n-6 and 20:5n-3, were measured in plasma and stimulated blood cell s. Levels of TXB, were greatest in fish fed the BO/TO diet compared to both other treatments, while LTB, was decreased in fish fed the BO/MO diet compared to both other treatments. In a stress test which involv ed anaesthesia followed by measurement of recovery times, fish fed the BO/MO diet had significantly lower recovery times compared to fish fe d the FO diet.