Effects of Aquaculture Water Environment on Fish Digestion: A Review

The digestive system is a vital organ system for maintaining nutrient metabolism and overall health in fish, and its proper functioning is fundamental to ensuring growth performance and health status. Environmental factors in aquaculture water, including temperature, dissolved oxygen, ammonia-nitrogen, nitrite, pH, salinity, water hardness, and aquatic pollutants, are key factors affecting digestive function. Numerous studies have shown that these factors directly affect digestive enzyme activities, disrupt intestinal mucosal integrity, and interfere with gastrointestinal motility. In addition, they indirectly regulate energy metabolism during digestion and modulate the composition of intestinal microbiota, thereby exerting effects on digestive function. These factors also act through specific signaling pathways that indirectly regulate digestive function. Specifically, dissolved oxygen, ammonia-nitrogen, and pH mainly affect the HIF-1α and AMPK pathways; temperature and dissolved oxygen primarily influence the mTOR pathway; and ammonia-nitrogen, nitrite, and aquatic pollutants mainly affect the NF-κB and Nrf2 pathways. This review may provide a reference for the precise regulation of aquaculture water environments and for the management of fish digestive health.