Objective The study aims to investigate the effect of culture density on the water quality of American black bass (Micropterus salmoides) and the nutritional quality of fish.

Methods With M. salmoides as the research object, two experimental groups with low and high densities were established , five water samples were collected from ponds with different culture densities, and four M. salmoides samples were randomly collected for perform testing and analysis of biological indices, muscle nutritional composition, and textural characteristics. The culture densities of the low-density group ranged from 90 000 to 93 334 ind·hm²⁻, and those of the high-density group ranged from 150 000 to 152 500 ind·hm²⁻.

Results It was found that the contents of dissolved oxygen, total phosphorus and chlorophyll a in the cultured water of the high-density group were significantly lower than those of the low-density ponds (P<0.05), and that the contents of total nitrogen, nitrite and chemical oxygen demand (COD) were significantly higher than those of the low-density group (P<0.05). The abundance of diatom phylum, green algae phylum and cyanobacteria phylum were significantly greater in the low density group than in the high density group (P<0.05). In addition, the Chao and Ace indices of the bacterial community in the water column of the high-density group were significantly lower than those of the low-density group (P<0.05); at the phylum level, Actinobacteria and Ascomycetes were both dominant in two experimental groups, but there was no significant difference between the high- and low-density groups (P>0.05). In terms of muscle nutritional quality, the hardness, shear force, chewiness and adhesion parameters of M. salmoides muscle were smaller in the high-density group than in the low-density group (P<0.05); muscle crude protein and crude fat were significantly higher in the low-density group than in the high-density group (P<0.05).

Conclusion High-density aquaculture exacerbates water eutrophication and ecological imbalance, thereby exerting negative impacts on the nutritional quality of M. salmoides muscle. Therefore, it is imperative to rationally regulate stocking density and optimize aquaculture water quality to maintain the stability of the aquatic environment and ensure the nutritional value of farmed fish.