Although multiple herbicide exposures are more prospective to occur in water, many previous studies were carried out as single herbicide exposure. To investigate the toxic effect of prometryn on cyanobacteria and water qualities, single and double prometryn exposures (at different growth phases) on Microcystis aeruginosa growth and concentrations of nutrients were compared after a 44-day experiment. Results indicated that under single exposure, maximum inhibition rates were 4.7–12.0% higher than those under double exposures. Correspondingly, the maximum Microcystis aeruginosa densities and growth rates under single exposure were 10.3–21.1% and 19.5–37.7% lower than those under double exposures (p < 0.05), respectively. These findings revealed that repeated prometryn exposures resulted in a reduction in biological effects, because the time of application and the concentration injected during the first application were both significant factors in the biological effects of prometryn. Prometryn exposure scenarios did not have a significant effect on nutrient or nutrient consumption concentrations (p > 0.05). In general, the pattern of nutrient limitation showed a shift from phosphorus to nitrogen limitation. The quantified relationships between Microcystis aeruginosa growth rates and consumed nutrients were studied. Based on the above findings, we believe that a high-dose and single prometryn exposure is a more effective exposure pattern for limiting cyanobacteria growth.

To investigate the toxic and environmental effects of prometryn, a laboratory experiment was performed on coexistent fish and algae. The body weight and length of Carassius carassius, Microcystis aeruginosa (M. aeruginosa) densities and water quality were measured continuously for 92 days. It was observed that fish growth was significantly inhibited by prometryn. This can be partly attributed to the adverse effects of prometryn on the antioxidant system of fish; the activities of superoxide dismutase (SOD) and catalase (CAT) in crucian carp were significantly inhibited by prometryn. The growth of M. aeruginosa was greatly inhibited by prometryn (p < 0.05), and the adverse effects of prometryn on M. aeruginosa indirectly impacted water qualities. The body weight and length of Carassius carassius first increased and then tended to be stable with increasing electrical conductivity (EC) values; their quantified relationship was established based on the Gompertz and Logistic equations (R² = 0.920–0.989). Based on the above results, we concluded that the toxic effects of prometryn can impact the antioxidant system of fish and algae which in turn affects their growth performance, and have an indirect impact on water quality. The application of equations made it realizable to obtain a more detailed interpretation of the processes involved in these biological–abiotic interactions.

The effects of three types of feed, purchased from online stores and having similar prices, on the growth performance and culture environment of crucian carp (Carassius auratus) were studied in this experiment, which aimed to provide a reference for the evaluation and selection of fish feed. The results showed that feeding different feeds had a significant effect on crucian carp, and that the growth-promoting effect of HD feed (feed produced by Haida Company Limited) was significantly better than that of the other two feeds. For example, the weight gain rate (WGR) of fish in the HD group was 47.1% higher than that in the LD group (p < 0.05), and the WGR of fish in the LD (feed produced by Lianda Company Limited) group was 81.4% higher than that in the TW (feed produced by Tongwei Company Limited) group (p < 0.05). Moreover, the activities of superoxide dismutase and catalase in fish in the HD group was significantly higher than that in the LD and TW groups. Furthermore, we found significant differences in the environmental effects of feeding different feeds. Compared to the LD and HD groups, the environmental impacts for the TW group were more pronounced. The body weight of crucian carp first increased and then stabilized with increasing total dissolved solids (TDS) values. Their quantitative relationship was established based on the von Bertalanffy and Logistic equations (R² = 0.942–0.995). The results above indicate that, due to differences in feed formulation and the quality of feed raw materials, different feeds have a significant impact on the growth performance and antioxidant indices of fish, as well as on the water environment. Therefore, selecting the appropriate feed is crucial for promoting high-quality development in the aquaculture industry.

An experimental study was conducted in the laboratory to investigate the interactive effects of fish and algae on growth patterns and water quality. Body length and body weight of Carassius carassius, Microcystis aeruginosa (M. aeruginosa) density, and concentrations of nutrients were monitored continuously over a period of 92 days. It was noted that fish growth was significantly higher in the absence of M. aeruginosa compared to its presence (p < 0.05). This can be partly attributed to toxin production by M. aeruginosa. The densities and growth rates of M. aeruginosa in groups with Carassius carassius were significantly higher than those in fishless groups (p < 0.05), and this was attributable to fish metabolism and bioturbation, which led to a considerable increase in ammonia and total dissolved nitrogen concentrations, as well as a significant impact on proportions of nutrients. The growth rate of Carassius carassius firstly increased and then decreased with increasing M. aeruginosa densities, and a quantitative relationship was established using the Gompertz equation and Logistic equation (R² = 0.914–0.955). Based on the above results, we concluded that interactions between fish and algae are greatly related to their consequences on water qualities, by employing equations, a more detailed interpretation of the processes occurring in the fish–algae system can be achieved.