Dietary fish oil replacement by soybean oil: Effect on plasma vitellogenin, sex steroids and ovarian steroidogenesis in Chinese strip-necked turtles (Mauremys sinensis )

Abstract

In order to investigate the effects of dietary fish oil replacement, the turtles (Mauremys sinensis) were fed four experimental diets for 10 months: FO (100% fish oil), FSO (70% fish oil and 30% soybean oil), SFO (30% fish oil and 70% soybean oil) and SO (100% soybean oil), sampled at pre-vitellogenesis, vitellogenesis and post-vitellogenesis. The results showed that plasma gonadotropin-releasing hormone (GnRH) levels were the highest at pre-vitellogenesis, which promoted the secretion of gonadotropin and sex steroids. Therefore, plasma luteinizing hormone (LH) and estrogen (E2) levels were significantly increased at post-vitellogenesis (p < 0.05), while follicle-stimulating hormone (FSH) levels increased at vitellogenesis (p < 0.05). The FO and FSO groups had significantly higher GnRH and E2 levels than the other two groups (p < 0.05). In addition, plasma vitellogenin (Vtg) levels significantly increased at vitellogenesis and post-vitellogenesis (p < 0.05), which were significantly higher in the groups of FO and FSO than SO (p < 0.05). Moreover, the expression levels of hepatic estrogen receptor α (Erα) mRNA were significantly increased at vitellogenesis and post-vitellogenesis while ovarian Cyp19α1α mRNA were significantly increased at post-vitellogenesis (p < 0.05), and both were the lowest in SO. Taken together, the replacement of fish oil with 66.7% soybean oil is feasible.