Effect Of Saline-alkali Stress On Oxygen Consumption, Osmoregulation And Ionic Regulation Of Przewalski’s Naked Carp, Gymnocypris Przewalskii

Gymnocypris przewalskii is the most important commercial fish endemic to theQinghai Lake, which survived and grown in high saline-alkali environment. In thegrowth process, the fish can adapt to the huge variation of salinity and alkalinitythrough self-regulation. In recent years, the number of G. przewalskii has decreaseddramatically due to over-fishing and deteriorated habitat. In this view, the fish grows ina unique environment and has migratory spawning habits, which can be as a goodsaline-alkali-tolerant research material. Acute toxic experiments, respiratory physiology,blood physiology and histochemical test was investigated after transferring the juvenileand adult G. przewalskii directly from freshwater to saline-alkali water.（1） Acute toxic experiments were carried out to test the tolerance of juvenile G.przewalskii to salinity and carbonate alkalinity. The results showed that:①The LC50values of salinity to juvenile G. przewalskii was21.15,18.85,18.32and18.20in24h,48h,72h and96h. G. Przewalskii is very sensitive the salinity higher than18;②TheLC50values of carbonate alkalinity to juvenile G. Przewalskii was165.02,158.13,153.53and150.18mmol·L^-1in24h,48h,72h and96h, the fish has strong tolerance tocarbonate alkalinity.（2） The oxygen consumption and suffocation point under saline-alkali stress wasinvestigated through transferring the juvenile and adult G. przewalskii directly fromfreshwater to saline-alkali water. The results showed that:①The oxygen consumptionof juvenile and adult G. przewalskii at the different points among treatments was notsignificantly（P>0.05） different within96h exposure, except significantly high （P<0.05）oxygen consumption to juvenile fish in the carbonate alkalinity of56.50±0.03mmol·L^-1treatment and oxygen consumption to adult fish in the salinity of15.05±0.01treatmentthan that in freshwater treatment at3h post exposure. G. przewalskii has strongtolerance to saline-alkali water, it can restore to normal breathe level quickly under saline-alkali stress through special regulation, and need low energy in this process.②G.przewalskii has strong tolerance to hypoxic environment with the suffocation point of0.14-0.17mg·L^-1.（3） Osmoregulation and ionic regulation under saline-alkali stress was investigatedthrough transferring adult G. przewalskii directly from freshwater to saline water,carbonate alkalinity water and saline-alkali mixed water. The results showed that:Concentration of ions （Na+, Cl-, Ca2+） and osmolality in the plasma of the fish betweencarbonate alkalinity treatment and the control was not significantly different within96hexposure, however, the ions and osmolality were significantly higher in salinity-waterand mixed-water treatments than that in the control. The peak occurred at72h postexposure. G. przewalskii has strong tolerance to saline-alkali water, which was able toadapt to saline-alkali environment quickly through osmoregulation and ionic regulation.（4） The histochemical variation of juvenile G. przewalskii under saline-alkali stressafter96h post exposure was investigated by paraffin section, the results showed that:Compared with the control, gill lamellae were shorten and bent, and the base of the gilllamellae were thicken. The nephridial globe were atrophy and the antrum of uriniferoustubule were aggrandizement in kidney. But the posterior region of the intestine were notchanged. The regulation strategy in histochemical level of G. przewalskii exposed tosaline-alkali stress need further study.In summary, G. przewalskii has strong tolerance to salinity, and has very strongtolerance to carbonate alkalinity. It is able to adapt to saline-alkali environment quicklythrough osmoregulation and ionic regulation with low energy consumption in thisprocess. The fish has strong resistance to hypoxia environment. The strong tolerance ofG. Przewalskii to saline-alkali water and hypoxia environment could benefit fromlong-term natural selection and evolution.