Exposure to an environment containing microplastics can cause adverse effects on creatures through respiratory and digestive systems. In this paper, 50–500 μm polystyrene microplastics (exposure concentrations were 200 μg/L, 800 μg/L, and 3200 μg/L concentrations) were selected to study the distribution of polystyrene microplastics (PS-MPs) and the effects on the growth, development, tissue damage and gene expression of crucian carp juveniles. The results showed that PS-MPs were enriched in the intestinal tract (GIT) and gill tissue of crucian carp, and the average number of PS-MPs was between 0 to 2.33 items per individual. It was found that the average number of MPs in the intestine was more than in the gills, and it was independent of the PS-MP concentration. However, the specific gravity of PS-MPs in excreta was concentration-dependent. In addition, it was found that the exposure of the medium concentration group promoted the weight of the crucian carp larvae, inhibited the growth rate, and reduced the weight in the low and high concentration groups. The histopathological results indicated that the intestinal, gill, brain, and liver tissues all showed different degrees of damage, and the higher the concentration of PS-MPs, the more severe damage to the tissue cells. This experiment evaluated 15 genes in three treatments, which found that PS-MPs had different effects on gene expression in the liver, intestine, and gill tissues, and the tested genes were involved in different response pathways associated with virulence.

Using fish as indicator organisms to monitor water quality can accurately reflect the pollution status of aquatic environments in real time. Currently, there are limited quantitative and empirical studies on fish movement behavior. An experimental study on the fish movement behavior response during water quality change was conducted using an aquatic environment model. Advanced acoustic tag monitoring technology was used to qualitatively and quantitatively assess fish movement. Using the temporal and spatial distributions of fish motion behavioral trajectories during water quality change, the fish behavior response indicators were the distance between the fish and the source of pollution, the distance between the fish and the water surface, and fish swimming speed. The fish were sensitive to water quality factors, including dissolved oxygen (DO) content, microcystin aeruginosa toxin (MC-LR), and non-ionic ammonia (NH₃). The correlations between indicator pairs were analyzed. A new water ecological health evaluation system based on these indicators was constructed, and aquatic ecological health in the field was evaluated using the new system. The evaluation showed a sub-healthy state in spring and a slightly morbid to morbid state in summer, which was consistent with the results based on water quality indices. The accuracy of the proposed assessment system was verified. This showed that the assessment method and grade division of the assessment system were reasonable and feasible and could reflect the health status of the aquatic ecological environment in real time. This study provides a basis for the assessment of the health and restoration effects of the aquatic ecological environment.