Influence of long-term temperature stress on respiration frequency, Na/K-ATPase activity, and lipid metabolism in common carp (Cyprinus carpio).

Temperature is a key factor that influences fish metabolism. Therefore, it is important to understand how temperature variation affects lipid metabolism and energy consumption in fish. We determined respiration frequency, Na/K-ATPase activity, and lipid metabolism in common carp (Cyprinus carpio) after 18 days of temperature stress (5 °C and 30 °C, with 17 °C as the control). We found that respiratory frequency was positively correlated with water temperature (p < 0.01), whereas red blood cell count and mean corpuscular hemoglobin content and concentration were negatively correlated with temperature. In liver and heart, triglyceride (TG) levels were lower in both stress groups (5 °C and 30 °C) than in the control (17 °C) (p < 0.01), and highest in muscle from the high temperature stress group (p < 0.01). The non-esterified fatty acid concentration was negatively correlated with TG levels. In brain, lipoprotein lipase (LPL) activity decreased with increasing temperature and hepatic lipase (HL) activity was lower in both stress groups than in the control (p < 0.01). In muscle, the activity of LPL and HL was lowest in the high temperature stress group, resulting in a significant increase in TG levels. Na/K-ATPase activity in heart was lower in both stress groups than in the control (p < 0.01). The expression of LPL mRNA in heart increased with increasing temperature (p < 0.01), whereas LPL mRNA expression in brain and liver increased in both stress groups (p < 0.01). Our results show that temperature can significantly affect lipid metabolism in common carp, and that different tissues respond differently to changes in temperature.