Bile salt dietary supplementation promotes growth and reduces body adiposity in gilthead seabream (Sparus aurata)

The present study aimed to evaluate the effect of dietary supplementation using bile salts (BSs) on several key performance indicators like growth and feed performance, fat accumulation and tissue condition in gilthead seabream (Sparus aurata). A 90-day feeding trial was conducted in juveniles of gilthead seabream (initial body weight, BW = 44.0 ± 4.2 g) that were fed three isoproteic (44% crude protein), isolipidic (18% crude fat) and isoenergetic (21.4 MJ kg−1) diets rich in saturated fats to favour lipid accumulation. One diet was used as a control and the others were supplemented with graded levels of a BS blend: 0.06 (BS0.06%) and 0.12% (BS0.12%). At the end of the trial, a significant increase in BW and a decrease in the levels of perivisceral fat were observed in fish fed the BS0.06% diet. However, only the BS0.12% diet significantly enhanced lipid digestibility, as indicated by the higher coefficient of apparent lipid digestibility and increased activity of the pancreatic bile salt-activated lipase. None of the diets modified the fatty acid profile of liver or fillet. In addition, while only the BS0.06% diet decreased fat deposits in liver, both BS-supplemented diets reduced fat accumulation in the intestine. Furthermore, dietary BS inclusion modified the bile acid profile in the gallbladder and anterior intestine, increasing the content of taurodeoxycholic acid in both tissues and decreasing the content of taurochenodeoxycholic acid in the gallbladder when supplementing the diet at an inclusion level of 0.12% of the BS blend. The gene expression profile of liver was analysed by quantitative PCR, targeting biomarkers mainly related to lipid metabolism and antioxidant defense, and few differences were found among dietary treatments. It was noteworthy that the decrease of lipoprotein lipase expression in fish fed the BS0.06% diet may be correlated with their reduced perivisceral fat and lipid accumulation in the liver, while the increase of the fatty acid synthase expression might help maintaining hepatic fatty acid levels stable. The higher gene expression of peroxiredoxin 5 was also noticeable and might be the cause of the lower catalase activity on the liver of fish fed the BS0.06% diet. Summarizing, we recommend the 0.06% BS dose to enhance growth performance and reduce perivisceral, hepatic and intestinal fat of gilthead seabream without comprising their health, but further studies still need to be performed for deciphering the mechanisms by which BSs act in fish lipid metabolism.