Liver alterations induced by long term feeding on commercial diets in Atlantic halibut (Hippoglossus hippoglossus L.) females. Histological and biochemical aspects

In the absence of a specific diet for Atlantic halibut, the commercial brood stocks are fed different and randomly chosen diets, ranging from frozen fish to commercial dry feeds and premix. Since egg quality is largely dependent on the vitellogenin synthesised in the liver, hepatohistology of Atlantic halibut female brood stock and recruits was used to screen long-term effects of 3 diets commonly used in intensive production, with livers of wild caught females as reference. Specific differences in liver histology were observed between the 3 different diets and the wild specimens. A severe macrovesicular steatosis was observed in females fed supplemented herring. The hepatomegaly and the profound histological changes observed in these females address the functionality of the liver. Females fed a wet diet showed a moderate lipid and glycogen accumulation, while specimens on a dry marine diet presented an important glycogen accumulation with lipid inclusions. Macrophage aggregates were observed in all specimens and the volume density was not significantly affected by the diet. Broad variations could be observed between individuals of a same group. Hemosiderin, melanin and ceroid deposition was limited in all specimens. The biochemical analyses confirm that diets had a significant effect on total lipid content. Both dry feed and herring diets gave significantly higher hepatic lipid contents than moist diets (P = 0.0002 and P = 0.0026) and natural diet (P = 0.0026 and P = 0.0223). Significant differences between diets were also found for the major PL classes. Dry feed and herring diets gave lower PL content than moist (P < 0.0001 and P = 0.0064) and natural diet (P < 0.0001 and P = 0.0105). Principal component analysis run on FAMES indicated that the diets separate roughly into 4 clusters. The main difference between wild specimens and females fed herring were observed in the content of long chain MUFA (C ≥ 20) and accumulation could play a role in the development of hepatosteatosis. Thus, herring or derivates are not recommended as brood stock diet. Liver can be used as a biomarker in brood stock nutrition studies for Atlantic halibut and possibly for other marine species as well.