Differences in swimming ability and its response to starvation among male and female Gambusia affinis

To explore the differences in the swimming ability and environmental adaptive abilities between male and female Gambusia affinis, we assessed the differences in burst swimming speeds (U(burst)), critical swimming speeds (U(crit)) and their related fin areas, and consumption of energy substances after starvation at 0 (control group), 15, 30, 45, and 60 days, respectively. The results showed that the pectoral and caudal fin areas did not differ significantly between male and female G. affinis. However, the dry mass, condition factors, and absolute contents of glycogen, lipids, and proteins were significantly elevated in females in the control group (P<0.05), whereas U(burst) and U(crit) were significantly low (P<0.05). After starvation of 60 days, the rate of consumption of lipids was significantly low in the females (P<0.05). Although U(burst) and U(crit) decreased linearly with increased duration of starvation, the coefficient of linear equation between U(crit) and starvation time was significantly lower in females than males (P<0.05). These findings indicated that low body mass and condition factors reduce the relative bear load and moving resistance that causes high swimming performance in male G. affinis. High contents of energy substances and low rate of consumption of lipids result in stable U(crit) in females during hunger.