Effects of Aquatic Plants on Water Quality, Microbial Community, and Fish Behaviors in Newly Established Betta Aquaria

Maintaining water quality and fish well-being in newly established, small, unfiltered betta (<i>Betta splendens</i>) aquaria is a significant challenge. To improve betta fish breeding and welfare, this study set up four groups: the <i>Sagittaria subulata</i> (<i>S.su</i>) group, the <i>Alternanthera reineckii</i> (<i>A.re</i>) group, the <i>Wolffia globosa</i> (<i>W.gl</i>) group, and the plant-free (CG) group. We evaluated the effects of aquatic plants on water quality, fish behavior, and microbial community in newly established tanks over 25 days. The results demonstrated that both the dissolved oxygen (DO) and potential of hydrogen (pH) decreased with the experimental duration, while ammonia nitrogen (NH₃-N) increased over time in all groups. Compared to the CG group, all aquatic plants significantly reduced the NH₃-N accumulation. The <i>S.su</i> group exhibited the lowest mean NH₃-N concentration of only 0.14 mg·L^-1, which was considerably lower than that of the other groups (<i>p</i> < 0.05). The behavioral analysis revealed that, during the 25-day randomized monitoring period, bettas in the <i>S.su</i> group exhibited the lowest surface breathing, with an average of only 0.36 events per 5 min, which was significantly lower than that of the CG group (<i>p</i> < 0.05). Additionally, the <i>S.su</i> and <i>W.gl</i> groups demonstrated longer average swimming durations than the other groups, suggesting a potential trend toward improved welfare in betta fish. Aquatic plants shaped the microbial diversity and composition within the experimental aquatic system. The <i>W.gl</i> group had the highest microbial diversity, and the <i>A.re</i> and <i>S.su</i> groups enriched Verrucomicrobiota. These results demonstrate the preferential shaping of microbial communities by aquatic plants, suggesting a potential pathway for enhancing water quality. In conclusion, <i>S. subulata</i> demonstrates the greatest benefits under the experimental conditions, making it a more suitable choice for this experiment.