Effect of alternative oil sources at different dietary inclusion levels on food intake and appetite regulation via enteroendocrine and central factors in juvenile Solea senegalensis (Kaup, 1858)

Vegetable oils (VO) are increasingly used to substitute fish oil (FO) in aquafeeds in order to meet demands of the rapidly growing aquaculture industry. However, effects of dietary VO on appetite and food intake have hardly been investigated, despite the importance of these factors for determining growth and body composition of cultured fish. This study analyzes the effects of an alternative dietary oil source (75% FO replaced by VO, compared to 100% FO) included at different lipid levels (8% or 18%, at the expense of carbohydrates) on voluntary food intake (VFI) and on the expression of putative appetite–regulating genes in the intestine and brain of Senegalese sole (Solea senegalensis) juveniles before and after a meal. Decreased VFI was observed only in fish fed the 18FO diet, indicating a higher satiating effect of FO compared to VO at equally high dietary lipid levels. However, no obvious relationship was found between the VFI results and mRNA levels of the analyzed peripheral or central genes. Several putatively anorexigenic peripheral genes (pyya, pyyb, glp1) had higher basal expression in fish fed lower lipid diets whereas, 6h after a meal, only pyyb and the orexigenic gal showed higher expression in the 8% lipid treatments. Conversely, basal mRNA levels of central neuropeptides were generally not regulated by diet, but most showed postprandial changes, with some slight differences in relation to lipid/carbohydrate level. Of all the studied genes, only the anorexigenic cocaine– and amphetamine–regulated transcript 1a and 1b were affected by dietary lipid source, with higher postprandial mRNA levels in fish fed FO, 1h and 3h after feeding the 18FO and 8FO diets, respectively, possibly relating to the decreased VFI of the 18FO treatment. This study provides new information on several key genes believed to be involved in the regulation of appetite and how they are affected by dietary lipid properties in Senegalese sole.