Saline-alkaline water bodies are widely distributed in China. High alkalinity is one of the main stressors for the survival of aquatic animals in saline-alkaline water. Previous studies have established that ammonia excretion is inhibited when fish are acutely exposed to alkaline water. Przewalskii's naked carp, also known as or the scale-less carp, is endemic to the austere environment of Lake Qinghai. Lake Qinghai has a high salinity (13 ppt) and a strong alkalinity (carbonate alkalinity approximately 29 mmol/L, pH 9.1-9.5). Due to high evaporative water loss and extensive water diversion for agricultural use, the water level of the lake is decreasing by 10 cm per year and the salinity and alkalinity levels are increasing by 7% and 0.5% per year, respectively. Some studies showed that had evolved a variety of mechanisms, such as osmoregulation and ion regulation with low energy consumption, regulation of HCO3-secretion in intestines, and compensatory carbonic anhydrase expression mechanism under metabolic alkalosis, to adapt to saline-alkaline environments. However, the mechanism of nitrogenous waste excretion is less well studied. In order to evaluate the effect of carbonate alkalinity stress on nitrogenous waste excretion in to 32 mmol/L and 64 mmol/L carbonate alkalinity water and measured ammonia and urea excretion rate after -6 h (pre-transfer), 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 48 h, 72 h, 96 h, and 120 h (recovery) after initial exposure. We also measured Rhesus type b glycoproteins (), and urea transporter ( by real-time PCR. The results showed that in alkaline water reduced ammonia excretion but increased urea excretion. Ammonia excretion rate decreased significantly over the entire exposure period in 32 mmol/L carbonate alkalinity water and the initial exposure period in 64 mmol/L carbonate alkalinity water. Ammonia excretion is expected to be inhibited when fish are subjected to alkaline water because of a decrease in the extent of the protonation of NH₃ to NH₄⁺. Consequently, at high pH water caused by high carbonate alkalinity, the partial pressure of NH₃ (PNH₃) is predicted to rise in water adjacent to the gill, thus reducing the PNH₃ gradient that drives NH₃ diffusion. However, in the 64 mmol/L group, the ammonia excretion rate recovered to the level of pre-transfer after 24-72 h and 8-20 h. This indicated that 3 partial pressure gradient under high carbonate alkalinity. Urea excretion rate increased significantly after 12-16 h and 20-24 h in 32 mmol/L carbonate alkalinity water and 16-48 h in 64 mmol/L carbonate alkalinity water. The real-time PCR results showed that genes were up-regulated under carbonate alkalinity stress. The expression of in gills was significantly up-regulated after 12 h in 32 mmol/L carbonate alkalinity water, while was significantly up-regulated in gills after 6 h, 48 h, and 72 h and in kidneys at 6 h in 64 mmol/L carbonate alkalinity water. expression in gills was significantly up-regulated after 6 h in the 64 mmol/L carbonate alkalinity group. These results revealed that although ammonia excretion was inhibited in highly alkaline environments, and expression, recovering ammonia excretion, and excreting more urea. This study provided evidence of the nitrogenous waste excretion mechanism in in high alkaline environments. We speculate that the special mechanism of nitrogenous waste excretion facilitate the adaptation of to highly alkaline environments. Nonetheless, these findings raise more questions than answers, and further studies are needed to clarify the distribution and expression level of Rh protein in cells and tissues.