Dietary ratios of n-3/n-6 fatty acids do not affect growth of Nile tilapia at optimal temperatures (28°C) nor at temperatures that simulate the onset of winter (22°C)

Nile tilapia (Oreochromis niloticus) juveniles were fed diets containing 13 g/kg total polyunsaturated fatty acids (PUFAs) at different n-3/n-6 dietary ratios (0.2, 0.5, 0.8, 1.3 and 2.9) for 56 days, at 28 degrees C. Subsequently, fish were submitted to a winter-onset simulation (22 degrees C) for 33 days. PUFA n-3/n-6 dietary ratios did not affect fish growth at either temperature. At 28 degrees C, tilapia body fat composition increased with decreasing dietary PUFA n-3/n-6. Winter-onset simulation significantly changed feed intake. The lowest dietary n-3/n-6 ratio resulted in the highest feed intake. At both temperatures, body concentrations of alpha-linolenic acid, docosahexaenoic acid, eicosatrienoic acid and docosapentaenoic acid decreased as dietary n-3/n-6 decreased. Body concentrations of eicosapentaenoic acid (EPA, 20:5 n-3) increased with decreasing concentrations of dietary EPA. The n-6 fatty acids with the highest concentrations in tilapia bodies were linoleic acid and arachidonic acid (ARA, 20:4 n-6). At 28 degrees C, SREBP1 gene expression was upregulated in tilapia fed the lowest n-3/n-6 diet compared to tilapia fed the highest n-3/n-6 ratio diet. Our results demonstrate that a dietary PUFA of 13 g/kg, regardless of the n-3/n-6 ratio, can promote weight gains of 2.65 g/fish per day at 28 degrees C and 2.35 g/fish per day at 22 degrees C.