Abstract:Temperature is one of the key environmental factors affecting the growth and physiological functions of fish. Both the physical activity and the feeding behavior of fish can be significantly reduced or even stopped at low temperature. In this case, fish may consume stored nutrients to stay alive. Rice field eel Monopterus albus is a subtropical freshwater fish with great commercial values. They are prone to diseases and have a high mortality rate in winter. Previous studies suggested that overwintering could significantly affect the intestinal digestive enzymes, the immune and antioxidant functions (serum catalase and lysozyme), muscles and the liver lipid content of M. albus. However, changes in nutrients and physiological adaption during overwintering have been unclear. In this study, we conducted a 124-day experiment to investigate effects of overwintering on the body biochemical composition and partial serum biochemical indices of M. albus with the initial average body weight of (118.42±4.38) g. Results showed that after overwintering: 1) The compositions of the whole body, the liver and muscles of M. albus were significantly affected. The body crude lipid decreased compared to that before overwintering (P<0.05), whereas the body moisture and body crude ash were increased (P<0.05). The hepatosomatic ratio and the content of the liver glycogen were dramatically reduced (P<0.01), but the liver crude lipid was significantly increased (P<0.05). In muscles, the level of saturated fatty acids dropped (P<0.01), the content of polyunsaturated fatty acids rose (P<0.05), and the total amino acids and essential amino acids were markedly increased (P<0.01). 2) The serum triglycerides, glucose, total amino acids and essential amino acids became lower than those before overwintering (P<0.05), and the level of total serum proteins was greatly increased (P<0.01). However, there were no differences in the total cholesterol, the blood urea nitrogen, the aspartate transaminase and the alanine aminotransferase before and after overwintering (P>0.05). In conclusion, M. albus may consume the liver glycogen and body lipids to maintain life activities during overwintering, which consequently changes the compositions of amino acids and fatty acids in the muscle.
