Effects of dietary fish oil and corn oil on gonadosomatic and hepatosomatic index, gonadal histology, 17β-oestradiol level and fatty acids profile of mahseer (Tor tambroides) broodstock in captivity

The present research was conducted to investigate the effects of fish oil (FO) substitutions with corn oil (CO) on the gonad development of female Tor tambroides broodstocks, a high value freshwater fish. Three isonitrogenous (450 g kg⁻¹ crude protein) and isolipidic (105 g kg⁻¹ crude lipid) were formulated to contain FO and CO at a ratio of 1:0, 1:1 and 0:1, respectively, and fed to female fish (n = 10 fish × 3 replicate × 3 treatment; average weight = 910.0 ± 130.0 g) for five months. At the end of the feeding trial, there were no significant differences (p > .05) on the gonadosomatic index (GSI), hepatosomatic index, 17β-oestradiol (E2) concentration and muscle fatty acids (FA) composition. However, fish fed with diet containing FO to CO at a ratio of 1:1 demonstrated higher percentage of GSI, E2 concentration (ng ml⁻¹) and the presence of vitellogenic oocytes in the histological data compared to the other two feeding diets. The FA composition also highlighted that T. tambroides broodstocks can elongate polyunsaturated FA to highly unsaturated FA. Based on these preliminary results, it shows that T. tambroides prefer diets with supplementation of both n3 and n6 oil source. However, more studies need to be done to strengthen this conclusion.