Two groups of Anguilla japonica were treated with hormone, one on a weekly basis, the other on a biweekly basis. Intramuscular injection was applied at a dose of 0.75 mg/kg BW carp pituitary extract (CPE) plus 150 IU/kg BW human chorionic gonadotropin (hCG) for female fish, while males received half of this dose. The average total lipid content of the gonads from the weekly treated group, i.e. 20.6 ± 1.2 % for females and 18.0 ± 2.3 % for males, was significantly higher than the biweekly treated group, 16.8 ± 0.7 and 15.5 ± 1.3 %, respectively (p < 0.05). For both muscle and liver, the readings were not significantly different. The gonads from the weekly treated fish had more fatty acids, particularly saturated fatty acids, polyunsaturated fatty acids, highly unsaturated fatty acids, eicosapentaenoic acid (20:5n-3, EPA), docosahexaenoic acid (22:6n-3, DHA) and arachidonic acid (20:4n-6, ARA). Histological examination showed that the ovaries of both the weekly and the biweekly treated fish were mainly at stage IV. However, the weekly treated females had bigger oocyte diameter (722.0 ± 60.9 µm) than the biweekly females (611.6 ± 22.6 µm). These results suggest that CPE and hCG promoted the maturation process for both scheduled induction and that the frequency of hormone injection influenced the biochemical composition of gonads, especially their lipids. Our study describes for the first time the effect of hormone injection frequency on the lipid content and fatty acid composition in the gonads of A. japonica during artificial maturation. |
