Influence of dietary lipids on the fatty acid composition and stearoyl-CoA desaturase expression in hybrid tilapia (Oreochromis niloticus × O. aureus) under cold shock

To improve hybrid tilapia (Oreochromis niloticus × O. aureus) survival under cold shock, the influence of diets containing various dietary lipids was investigated. Four different diets were used which consisted of 12% fish oil, 12% palmitoleic oil 12% coconut oil, and a mixture of fish oil (7%) and corn oil (5%). Our results showed that during cold shock, the proportion of saturated fatty acids in the fish steadily and significantly decreased for all of the diets, but the proportion of monounsaturated fatty acids increased. Proportions of polyenoic fatty acids initially increased then stabilized for the mixed, fish, and coconut oil diets, but did not significantly increase until day 4 for the palmitoleic oil diet. The stearoyl-CoA desaturase (SCD) activity was the lowest on day 0 and then gradually increased for all diets. At any point, the enzymatic activity of SCD was the highest for fish on the mixed and the coconut oil diet, followed by the palmitoleic oil diet, and was lowest for the fish oil diet. The expression of SCD mRNA steadily increased for all diets, but increased more substantially for the mixed diet. On day 6, the expression was the highest for fish on the mixed diet, followed by the coconut oil diet, with the lowest levels for those on the palmitoleic and fish oil diets. These results show that dietary lipids strongly affect the fatty acid composition and SCD expression in tilapia under cold shock, and cold tolerance of this species is also affected.