Effects of fish oil on ovarian development in spotted scat (Scatophagus argus)

The effects of different concentrations of dietary fish oil (0, 2%, or 6%) on ovarian development in 2-year-old female Scatophagus argus were investigated. The levels of serum sex steroid hormones (estradiol-17β, E2; testosterone, T), protein phosphorus (SPP), and protein calcium (SPC), as well as vitellogenin (vtg) mRNA expression in livers and ovaries were measured. Over the eight week experimental period, oocytes did not develop further and remained at phase III in fish fed with the control diet with no supplement of fish oil. Fish fed with 2% fish oil supplement had oocytes at transition phase from III to IV. Fish fed with 6% fish oil supplement had oocytes at late phase IV. Higher gonadosmatic index, serum E2, SPP, SPC, and liver vtg expression were found in 6% fish oil group compared to that in the 2% fish oil group (except E2) and the control group (P<0.05). In addition, vtg expression in livers was 600-1000 times higher than that in the ovaries. Gonadosmatic index, E2, and SPP, as well as liver vtg expression increased during the experiment and peaked at the end of experiment. However, hepatosomatic index, serum T, and ovarian vtg expression peaked at 4 weeks, and then decreased at 8 weeks, with no significant difference among the 3 groups. In summary, we showed that 6% fish oil supplementation in S. argus could effectively promote ovarian development, with associated increases in E2 secretion and increased liver vtg mRNA expression.