Effect of nitrite exposure on oxygen-carrying capacity and gene expression of NF-κB/HIF-1α pathway in gill of bighead carp (Aristichthys nobilis)

Nitrite (NO2−) contamination of water can severely impact the health of aquatic life and is a major concern for commercial aquaculture. In order to study the effect of nitrite on Aristichthys nobilis, we investigated the oxygen-carrying capacity, NF-κB/HIF-1α pathway, and the gill tissue structure under nitrite stress. In the current study, bighead carp (initial weight 180.05 ± 0.092 g) were exposed to nitrite (48.634 mg/L) for 96 h and then for 96 h recovery test. After nitrite exposure for 6 h, hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-κB (NF-κB) mRNA expression increased significantly in the gill of bighead carp (P < 0.05). After nitrite exposure for 12 h, hemoglobin (Hb) and methemoglobin reductase (MHBR) content in blood decreased significantly (P < 0.05); TLR4 mRNA expression increased significantly (P < 0.05). After nitrite exposure for 24 h, methemoglobin (MetHb) content increased significantly (P < 0.05). After recovery test, all the indicators except TLR4 mRNA expression level recovered to initial level. In conclusion, nitrite exposure can affect hemoglobin dynamics, as oxidization of nitrite by hemoglobin results in the reduction of Hb to MetHb leading to hypoxia and nitrite exposure can also result into gill tissue damage. In the face of nitrite exposure, NF-κB and HIF-1α mRNA expression level increased immediately to protect the body from oxidative damage and eased hypoxic condition caused by nitrite. It was also observed that nitrite damage is recoverable in Aristichthys nobilis, but it may be need more than 96 h.