Species-specific differential responses of Gymnocypris przewalskii and Gymnocypris eckloni to Cd²⁺ and Zn²⁺ stress

To investigate the effects of Cd²⁺ and Zn²⁺ stress on Gymnocypris przewalskii and Gymnocypris eckloni , we systematically evaluated their acute toxicity, antioxidant capacity, and non-specific immune function. Specifically, static bioassays were conducted with different concentrations of Cd²⁺ and Zn²⁺, and the fish were exposed for 24, 48, 72, and 96 h to determine LC₅₀ and SC. The activities of key antioxidant enzymes (SOD and CAT), immune-related enzymes (ACP and AKP) and the relative expression levels of genes associated with the NF-κB signaling pathway ( TAK1 , IKKα , IκBα , NF-κB , IL-8 , A20 , and TNF-α ) in the gills, kidneys, and liver were measured. The results showed the LC₅₀ values of both species gradually decreased with exposure time, and the LC₅₀ and SC of G. eckloni were significantly higher than those of G. przewalskii ( P < 0.05). SOD and CAT in the kidney and liver of both species were inhibited to varying degrees, whereas in the gills, these enzymes were initially activated and subsequently suppressed. ACP and AKP activities exhibited tissue-specific patterns, as ACP and AKP activities were significantly inhibited in the gills of G. przewalskii , while in G. eckloni , the activities of these two enzymes in the liver were initially inhibited but later recovered to normal levels. Gene expression analysis revealed distinct tissue-specific and species-specific modulation of the NF-κB pathway in two species. In conclusion, Cd²⁺ and Zn²⁺ exposure induced oxidative stress and inflammatory responses in both G. przewalskii and G. eckloni . However, G. eckloni demonstrated superior abilities in antioxidant compensation, dynamic regulation of immune enzymes, and precise modulation of the NF-κB pathway compared to G. przewalskii . These findings provide insights into the molecular mechanisms underlying the physiological adaptation of Gymnocypris species to heavy metal stress and offer a scientific basis for the conservation, artificial propagation, and ecological risk assessment of these endangered fish species.