Genetic Improvement of Farmed Tilapia (GIFT, Oreochromis niloticus) is the genetically improved tilapia obtained by gene improvement performed by World Fish Research Centre and Norwegian related organization. The GIFT grows fast, is genetically stable and can tolerate low temperature of 6-10℃ for short periods, and tolerate temperature as high as 35-42℃. Tilapia is extremely hardy but may be stressed by excessively high or low temperatures which increase susceptibility to pathogens.
Stress is the sum of an organism's nonspecific responses to various acute external and internal stimuli. It is an organism's physiological response to adapt to environmental changes, but excess response that inhibits immunity could lead to pathological change. In fish, excess stress can lead fish to diseased state, even to death. Cold temperature is an important ecological stressor, potentially leading to activation of the neuroendocrine pathway, including the hypothalamic-pituitary-interrenal axis, the hypothalamic-pituitary-thyroid axis, or the hypothalamus-autonomic nerves-chromaffin axis, increasing the release of cortisol, thyroid hormone, or catecholamines in vertebrates. Previous studies showed that cold stress resulted in altered serum lysozyme, complement activity and other related immune parameters in gilthead sea bream (Sparus aurata), and altered serum biochemical parameters of milkfish (Chanos chanos) such as glucose and triglyceride. It also changed activities of alanine amiotransferase (ALT) and aspartate transaminase (AST) of common carp (Cyprinus carpio) and large yellow croaker (Pseudosciaena crocea). Additionally, a study reported that cold stress increased the heat shock protein 70 (HSP70) level in Atlantic salmon (Salmo salar).
Information about the relationship among the changes of serum hormone (triiodothyronine, thyroxine and cortisol) concentrations, serum nonspecific complement (C3 and C4) and serum biochemical parameters (such as serum glucose, cholesterol, triglyceride, aspartate aminotransferase, alanine aminotransferase), although important for understanding the mechanism of stress effects, was not available. The mechanism of cold stress-induced immunomodulation in fish is not clear. The objective of this study was to investigate the effect of cold shock on the physiological function of GIFT strain of tilapia to gain a better understanding of the mechanism of coping with cold stress in this fish. The fish (body weight: (177±2.18)g) were randomly divided into two groups: a control group ((25±1)℃) and a treatment group ((9±1)℃). The experiments were repeated five times. Serum glucose, cholesterol, triglyceride, aspartate aminotransferase, alanine aminotransferase, complement 3, complement 4, lysozyme, cortisol, triiodothyronine, thyroxine concentrations and liver HSP70 mRNA level were determined at 0, 2, 6, and 12h after cold stress. The results showed that compared with the control group, the treatment group had the following serum parameters significantly increased: glucose level (P<0.05) at 6h, triglyceride levels at 2 and 6h, cholesterol levels at 6 and 12h, and alanine aminotransferase activities at 2 and 12h. The levels of complement 3, complement 4, and lysozyme in the serum decreased significantly (P<0.05) at 2,6 and 12h after cold stress whereas serum concentrations of aspartate aminotransferase, cortisol, and triiodothyronine increased significantly (P<0.05) at 2, 6, and 12h after cold stress. Additionally, liver HSP70 mRNA level was higher (P<0.05) at 12h after the cold stress. We suggest that acute cold stress might increase liver HSP70 mRNA, thereby affecting the physiological function and non-specific immune ability of GIFT tilapia.