Effects of the dietary linoleic acid to linolenic acid ratio for Nile tilapia (Oreochromis niloticus) breeding females

The present study was conducted to evaluate the effect of dietary linoleic acid/linolenic acid (LA/LNA) ratio for Nile tilapia (Oreochromis niloticus) breeding females. Four isonitrogenous (38% protein) and isolipidic diets were formulated to contain different dietary LA/LNA ratios (20.1; 4.5; 3.9 and 0.7) by increasing of linseed oil at the expense of corn oil. 96 fishes were stocked in twelve 250-L each tank and their reproductive performance assessed over 105 days. Reproductive and growth performances, fatty acid composition, total lipids in eggs, plasma profile of lipoproteins and estradiol and expression of steroidogenic genes on ovaries were examined. At the end of the experiment, fish fed the 3.9 and 0.7 LA/LNA diets produced higher number of eggs (p< 0.05). In general, the fatty acid profile of ovaries and eggs reflected the composition of the diet. The arachidonic acid content was higher in the 20.1 ratio and the eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids percentage, higher in the 0.7 ratio (p< 0.05). Diets did not influence the triglycerides content in plasma (p> 0.05). However, higher levels of cholesterol were observed in fish fed 4.5 and 3.9 LA/LNA diets (p< 0.05). The highest dietary LA levels increased the gene expression of cyp17, while the dietary 3.9 LA/LNA ratio promoted higher expression of cyp19a1a (p< 0.05). In conclusion, this study suggests that lower dietary n-6/n-3 PUFA ratio for Nile tilapia female should be used to highest expression of ovarian aromatase and better spawning performance.