To explore the impacts of acute ammonia nitrogen (NH₃-N) stress on gill structure and the antioxidant ability of red and white muscles in juvenile yellowfin tuna (Thunnus albacares), this study used natural seawater as a control, establishing two experimental NH₃-N groups at 5 and 10 mg/L. Gills and red and white muscle were taken at 6, 24, and 36 h for the determination of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GHS-PX) levels, and to observe gill structure. The results indicated that, with increasing time, the MDA concentration and CAT activity in the gills of the 5 mg/L group showed a trend of first increasing and then decreasing, while SOD activity exhibited a downward trend. In the 10 mg/L group, MDA concentration showed an increasing trend, while SOD, CAT, and GSH-PX activities demonstrated a trend of first increasing and then decreasing. In the 5 mg/L group, the MDA concentration and GSH-PX activity in the red muscle showed an increasing trend. In the 10 mg/L group, MDA concentration and SOD and CAT activities exhibited a downward trend. In the 5 mg/L group, the MDA concentration and SOD activity in the white muscle showed a downward trend, while CAT activity exhibited an increasing trend. In the 10 mg/L group, MDA concentration and CAT activity demonstrated a trend of first increasing and then decreasing, while SOD activity showed a downward trend. Ammonia nitrogen can lead to necrosis and shedding of gill epithelial cells, cell vacuolation, edema, as well as proliferation, hypertrophy, and fusion of secondary lamellae. This study demonstrates that NH₃-N can alter gill structure and reduce the antioxidant ability of gills and red–white muscle. The findings provide scientific data that can support the aquaculture and recirculating aquaculture systems of juvenile tuna.

Tuna aquaculture faces significant challenges from various pathogen-associated diseases, including bacterial, fungal, viral, and parasitic infections, which threaten both the health of farmed tuna and the economic viability of the industry. This review provides an overview of the current status of these diseases in tuna farming, with a focus on the pathogenic mechanisms, environmental stressors, and management strategies. Bacterial infections, particularly those caused by Vibrio species and Photobacterium damselae, remain major threats, often exacerbated by environmental stressors such as high water temperatures and poor water quality. Fungal diseases, which impact the gills of yellowfin tuna, and viral diseases, notably Nervous Necrosis Virus (NNV), present additional risks that result in high mortality rates, especially among juvenile fish. Parasitic diseases, including infestations by flatworms like Cardicola forsteri and ectoparasites such as Caligus species, also contribute to significant losses in tuna farming. Despite progress in understanding these pathogens, critical research gaps remain, particularly in the areas of immune system responses, pathogen-host interactions, and the development of sustainable disease control measures. The overuse of antibiotics and chemicals in disease management has led to growing concerns over antimicrobial resistance and environmental pollution. Future research should prioritize integrated disease management systems, including the development of eco-friendly control strategies such as probiotics, immunostimulants, and vaccines. Furthermore, the impact of environmental factors on disease dynamics requires more in-depth investigation, alongside the development of predictive models and real-time monitoring systems for better disease management. Addressing these challenges with a multidisciplinary approach will be crucial to improving the health and productivity of farmed tuna, thereby ensuring the sustainability of the tuna aquaculture industry.