Largemouth bass (Micropterus salmoides) is a major aquaculture species in China. Facility-based aquaculture, such as the “168” model, a high-efficiency recirculating system using funnel-shaped ponds, has promoted water conservation and improved aquaculture efficiency through structural innovation. However, fish die sporadically as the stocking density increases with increasing fish growth. To address this issue, three density groups were established, namely, low (2.5 ± 0.5 kg/m3), medium (4.0 ± 0.5 kg/m3), and high (7.5 ± 0.5 kg/m3). Histological examinations, biochemical assays, and transcriptomic and metabolomic analyses of liver tissues were performed, and fish health was comprehensively evaluated. Histopathological analysis revealed that progressive hepatic vacuolization and severe tissue damage occurred as the fish density increased. Biochemical indicators revealed that the immune system and growth underwent compensatory activation at medium density, shifting to immune suppression, growth impairment, and hepatic exhaustion at high density. Integrated omics analysis revealed that under medium-density stress, the urea cycle was impaired; under high-density stress, Ser metabolism in the liver was rerouted, potentially to overcome methyl donor depletion and prevent disorders of polyamine metabolism, accompanied by a gradual transition from compensatory activation to functional exhaustion. These findings improve our understanding of the physiological response mechanisms of fish to high-density stress. This study provides a theoretical basis for optimizing high-density aquaculture technologies such as the “168” model.
Yuan et al. (Tue,) studied this question.