Energy metabolism of tilapia hybrids（Oreochromis niloticus ×O. aureus）under cold shock

• Main Authors: Hsiao-Chen Lin, 林曉珍
• Other Authors: Ching-Ming Kuo
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/12638609326851165297

碩士 === 國立臺灣大學 === 漁業科學研究所 === 87 === Tilapia, an economically important cultured teleost in Taiwan, has played a significant role in the fisheries development in the past. As a tropical species, they are suitable for culture in the warm waters. However, mass mortality of these cultured tilapia resulted from less tolerable attributes of this species to the cold, has often caused tremendous loss for the tilapia culture industry, when the severe cold current approaches in the winter season. This study is therefore aimed to comprehend the physiological responses and energy metabolism of tilapias under the cold shock in order to delineate the pattern of energy metabolism and pathways under the cold. The acclimated tilapias at 25 C were rapidly exposed to varying temperatures of 25 ℃ , 20 ℃, 15 ℃ and 10 ℃, and the physiological responses and energy metabolism were monitored under various cold shocks. The parameters monitored included temperature tolerance, oxygen consumption, time-course changes in plasma glucose and lactate, and the enzymes involved in carbohydrate metabolism. The monitored enzymes included phosphofructokinase, pyruvate kinase and lactate dehydrogenase in glycolysis, fructose-1,6-biphosphatase in glyconeogenesis, glycogen synthase and phosphorylase a in glycogen metabolism, citrate synthase in Kreb’s cycle, and glucose-6-phosphate dehydrogenase in pentose shunt pathway. The kinetics of energy metabolism is quantitatively reflected by the changes in the enzyme activities. Adaptability to fluctuating environmental temperatures developed through adaptation and evolution, enable fish to survive and propagate in a variety of habitat niches. In consequence, fish have also developed mechanisms for capacity adaptation, by which physiological processes can be maintained homeostasis. Under the cold shock, fish will display behavioral responses and physiological regulations, by which fish are able to compensate their physiological processes to the environmental temperature changes. Remarkable hyperglycemic responses were detected in tilapias under the cold shock at 15 ℃, the plasma glucose rapidly increased from 63.91 mg/dl to 132.04 mg/dl in 6 hr, about two-fold increase over the original level. However, a slight elevation in plasma glucose, from 41.74 mg/dl to 57.15 mg/dl in 1 hr, was observed, when the tilapias were exposed acutely to 10 ℃. The hyperglycemic response at this lethal temperature was found less pronounced as compared to the previous. The observations suggested that the tilapias under 10 ℃ cold shock were unable to perform physiolozical regalation and compensation properly. The stress responses and the exhaustion of regulatory capability were indicated. With respect to the lactocemic responses under 15 ℃, the plasma lactate concentration depressed gradually from the initiation of cold shock treatment, decreased from 16.540.92 g/dl down to 12.110.28 mg/dl in 24 hr. At the extreme temperature of 10 ℃, the plasma lactate maintained at the constant level for 30 min, followed by a notable depression down to 9.472.24 mg/dl at the end of 1 hr, and eventually physical exhaustion and death . The changes in the oxygen consumption, which is a reliable biological indicator for the stress responses, was found highly correlated with the temperatures employed and sustained duration of cold shock. The pathway of energy metabolism shifted with persistence of cold shock stimulation. In hepatic tissues, glyconeogenesis and anaerobic pathway were dominant in the initial phase of cold shock at sublethal temperature, and aerobic metabolism was supplemented at the lethal temperature, while in the later phase, the energy were derived primarily through glycogenolysis and aerobic pathway. Similar observations were obtained in the muscular tissues in the initial cold shock period, but the pentose shunt pathway was the most important source of energy towards the later period of cold shock. Evidences suggested that the tilapias display temporal changes in the compensation strategy under cold temperatures.