Changes in the fatty acid composition and regulation of antioxidant enzymes and physiology of juvenile genetically improved farmed tilapia Oreochromis niloticus (L.), subjected to short-term low temperature stress

• Cold stress in short-term would enhance cortisol and antioxidant status.
• Serum glucose and cholesterol levels significantly decreased at 120 h post-stress.
• Tilapia mainly used saturated fatty acids as energy source firstly post-stress.
• Increased malondialdehyde was produced by oxidation of polyunsaturated fatty acids.

We evaluated the effect of cold shock on the fatty acid composition, antioxidant enzymes, and physiological responses of genetically improved farmed tilapia (GIFT). Experimental GIFT tilapia, a warm-water teleost, were initially acclimated at 28 °C and then transferred directly to 13 °C. Stress responses were monitored for 120 h. There was a significant change in all parameters in response to the cold stressor (P<0.05). Serum cortisol levels increased from 336.93 ng/ml to a peak of 1165.31 ng/ml 24 h after the initial cold shock, and declined rapidly thereafter. Serum glucose and cholesterol levels were significantly lower in the low temperature group than the control group at 120 h (P<0.05). Acute low temperature stress enhanced superoxide dismutase, glutathione peroxidase, catalase, and glutathione levels in the liver of GIFT tilapia. The GIFT tilapia were able to selectively metabolize fatty acids for energy needs during the early period of exposure to low-temperature stress. During this time, they primarily used saturated fatty acids for energy. However as the duration of the stressor and loss of muscle fat increased, the fish began to metabolize long-chain polyunsaturated fatty acids. Increased malondialdehyde was produced by oxidation of these fatty acids leading to oxidative damage. Our results provide insight into the changes in fatty acid metabolism physiology that allow GIFT tilapia juveniles to adapt to short-term cold stress.