Effects of dietary soybean lecithin on growth, tissue fatty acid composition, and gonadal development in the hermaphroditic rice field eel (Monopterus albus)

This study investigates the effects of soybean lecithin (SL) on the growth, fatty acid composition, lipid metabolism, and gonadal development of rice field eels. Fourteen-month-old eels were fed either fish oil diets or varying levels of dietary soybean lecithin (0 %, 1.4 %, and 2.8 %) for 10 weeks. Dietary SL had no significant impact on growth, whereas 1.4 % SL led to a significant decrease in moisture content and an increase in crude protein content in eels. The content of both saturated and polyunsaturated fatty acids increased in muscles fed the higher SL diet, with a concurrent decline in saturated fatty acids and an increase in polyunsaturated fatty acids detected in the liver. The expression levels of genes related to lipid synthesis, including accα and PPARγ, and genes related to polyunsaturated fatty acid synthesis, such as pla2g4a, fad2 and scd, were significantly increased in the liver of eels fed with 1.4 % SL diet. SL supplementation enhances lipid transport and antioxidant capacity in the liver, reduces fat deposition, and protects the liver from damage. Hepatosomatic index of fish in the SL1.4 % and SL2.8 % groups decreased. Supplementation of the diet with 1.4 % SL led to a significant decrease in the content of saturated fatty acids and an increase in the content of polyunsaturated fatty acids in the gonads, with a significant increase in arachidonic acid levels. The gonadosomatic index also increased with increasing dietary SL content. Rice field eels fed diets containing SL exhibited elevated serum levels of E2, delayed ovary-to-testis transition, and a preference for retaining the female state. In conclusion, dietary supplementation with SL increased the proportion of highly unsaturated fatty acids in the tissues, enhanced lipid metabolism in the liver, and improved antioxidant capacity. Furthermore, SL supplementation has been demonstrated to promote ovarian development and delay sex reversal in rice field eels.