Ammonia excretion and blood gas variation in naked carp (Gymnocypris przewalskii) exposed to acute hypoxia and high alkalinity.

Naked carp (Gymnocypris przewalskii), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combined hypoxia and high alkalinity. This study evaluated the effect of the interaction between carbonate alkalinity and hypoxia on ammonia excretion and blood gas variation in naked carp. Naked carp were subjected to normoxic, hypoxic and reoxygenation phases at two different carbonate alkalinity levels (CA0 = 0 mmol/L; CA32 = 32 mmol/L) for 4 days. The ammonia excretion rate (J _Amm ) of the CA0 group rapidly decreased under hypoxia and recovered under normoxia for four consecutive days. The J _Amm under CA32 also decreased under hypoxia and recovered to its previous level in the first 2 days. However, the J _Amm under CA32 was lower than that under CA0. The blood pO ₂ , sO ₂ of CA0 and CA32 group was significantly reduced under hypoxia, after which both groups recovered. Blood pCO ₂ of the CA32 group was lower than CA0 throughout the experiment. There were no changes in haematocrit of the naked carp exposed to carbonate alkalinity and hypoxia. The alkaline water increased the pH of the blood and contributed to increased haemoglobin O ₂ affinity. Overall, the present findings reveal that naked carp is a tolerant species that can maintain main ionic homeostasis under severe alkalinity and hypoxia. The high alkaline water is beneficial for naked carp to adapt to hypoxic environment.