STUDIES ON THE OXYGEN CONSUMPTION RATE AND ASPHYXIANT POINT OF MEGALOBRAMA PELLEGRINI AND COREIUS GUICHCNOTI

Both of Megalobrama pellegrini and Coreius guichcnoti are endemic fish in the upper reach of Yangtze River(from Yichang to Yibin).The construction of the hydroelectric projects,such as the Gezhouba Dam,the Three Gorges Dam,and hydropower cascade exploitation in the Jinsha River,drastically modifies physical environment and regulates flow in the Yangtze River course.This causes the habitats fragmentation to fish,blocks their migration routes,and destroys their spawning grounds,leading to the severe negative impacts on the rare and endemic fishes of the Yangtze River.Due to these reasons,it is forecasted that the population of these two kinds of fish might decrease sharply in the future.It becomes very urgent to take suitable countermeasures for conservation and resource-recovery.The oxygen consumption rate(OCR) and asphyxiant point(AP) are the important physiological indexes to fish culturing and breeding.In this experiment,the OCR and AP of these two kinds of fish were investigated by means of determining the dissolved oxygen in water.The method of respiratory chambers which were self-made had been applied.Two kinds of these experiment apparatus were used,one was done in sealed-still water,the other was done in sealed-flowing water.The temperature in the sealed respiratory chamber could be controlled.The oxygen consumption rate and the effect of body weight on the asphyxiant point of Megalobrama pellegrini were studied.The results demonstrated that,under the controlled temperature(15-27 ℃),the oxygen consumption rate of M.pellegrini increased while temperature rose,and decreased while body weight increased.The relationship between oxygen consumption rate and temperature can be described as y=0.036x-0.281(R2= 0.669,P0.01,n=15).The asphyxiant point decreased while body weight increased,but there was no significant difference(P0.05).The oxygen consumption rate of this fish ranged from 0.28 mg/g·h to 0.82 mg/g·h.In the temperature of 24.8 ℃,the fish that weight 1.3-3.2 g had a mean asphyxiation point of(0.91±0.08) mg/L and the range was 0.73-1.04 mg/L.The day and night change of oxygen consumption rate was studied on C.guichcnoti.The highest and lowest of the daily fluctuation of the oxygen consumption rate occurred at 3:00 and 21:00 respectively.The average oxygen consumption rate at night was much higher than that in the daytime.The result showed that this fish was more active at night.This phenomenon was identical with practice,and we found that this fish fed in night and slept in day.The fish that weight 21.8-46.3 g had a range of oxygen consumption rate from 0.64 mg/g·h to 0.18 mg/g·h under 23-27 ℃.The oxygen consumption rate decreased while the body weight of this fish increased.The relationship between oxygen consumption rate and body weight can be described as y=14.33x-1.08(R2=0.545,P0.01,n=21).The asphyxiant point of this fish was 0.95-1.63 mg/L,and the mean was(1.14±0.23) mg/L.Both of these two fish had high oxygen consumption rate and asphyxiant point.The results showed that the ability of low oxygen endurance of these two fish were much feeble than that of other fish.The present study can provide the basis of rational stocking,water quality management,bait feeding and transportation of live fish in artificial culturing production.