Ammonia‐‑nitrogen stress affects immune regulation via TNFα in yellow catfish (Pelteobagrus fulvidraco)

Abstract

Ammonia‑nitrogen has become a global issue with feed-dependent intensive culture modes, which may cause toxicity in aquatic animals by affecting immune regulation. Although numerous studies have investigated the acute and short-term toxic effect of ammonia‑nitrogen in fish, there is a lack of research on the long-term effects of exposure to low concentration of ammonia‑nitrogen. In this study, yellow catfish (Pelteobagrus fulvidraco) were exposed to water supplemented with ammonia (NH4Cl was used as the ammonia source) at concentrations of 0 (control), 8, 10, 12, 14, 16 and 18 mg/L for eight-weeks, and the effects on growth performance, histopathology, antioxidant and immune capacities of yellow catfish were investigated. The results showed that long-term ammonia exposure resulted in decreased weight gain rate (WGR) and serum antioxidant capacity, increased feed coefficient (FC), serum and tissue ammonia levels. They caused extensive histopathological changes and significantly impaired inflammatory and immune responses. On the other hand, ammonia exposure significantly affected the respiratory burst and the content of reactive oxygen species (ROS) of head kidney macrophages. Still, the above phenomenon can be reversed by inhibiting tumor necrosis factor-α (TNFα), indicating that TNFα may play a key role in this process. In conclusion, our findings indicate that extended exposure to ammonia nitrogen, even at low concentrations, has a detrimental effect on the well-being of aquatic organisms. This finding underscores the necessity of long-term environmental toxicological investigations of ammonia‑nitrogen.