Abstract
Hybrid red tilapia (& MALE; Oreochromis niloticus x & FEMALE; O. mossambicus), is a promising aquaculture species with many favorable commercial characteristics, as well as being a thermal sensitive species. The present study aimed to investigate the effect of increasing dietary levels of high polyunsaturated fatty acids (Aquafat-O (R); 0, 2, 4, and 6% kg? 1 diet, representing T0, T1, T2, and T3 respectively) on improving the cold tolerance of hybrid red tilapia. The fish were fed the experimental diets for 98 days at a rearing temperature of 25-26 C. Then all groups were exposed to cold stress (13 C) for 15 consecutive days (T0+), with maintaining half of the control group as a negative control (T0?). The body condition, behavioral, survival, and physiological responses were evaluated before and after cold stress. The results revealed that the low temperature exposure led to a decreased condition factor and induced several abnormal morphological and behavioral changes. The survival rate of cold-stressed fish was improved to 75.00% in T3 by feeding a high level of Aquafat-O (R), compared with 43.75% in T0+. Compared to the T0? before cold stress, red blood cells, hemoglobin, packed cell volume, T3 hormone, serum proteins, total cholesterol, and triglycerides were significantly decreased after being exposed to cold stress, which improved afterward with increasing Aquafat-O (R) levels. High levels of Aquafat-O (R) revealed high values of lymphocytes, and monocytes. In addition, cold stress caused a significant augmentation of serum cortisol and glucose levels, which was alleviated by dietary Aquafat-O (R) in a dose-dependent manner. In conclusion, the dietary inclusion of high levels of Aquafat-O (R) (6% kg? 1 diet) could improve unfavorable behavioral alterations, stress resistance, immunological responses, and boost the survival of hybrid red tilapia exposed to low water temperature.