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

## TL;DR

Adding aquatic plants like Sagittaria subulata improves water quality and betta fish behavior in small, unfiltered tanks.

## Contribution

This study shows that specific aquatic plants, especially Sagittaria subulata, reduce ammonia and improve fish welfare in betta aquaria.

## Key findings

- Sagittaria subulata significantly reduced ammonia nitrogen levels compared to other plants and the control group.
- Betta fish in Sagittaria subulata tanks showed longer active swimming times and fewer negative behaviors.
- Aquatic plants increased microbial diversity, with Sagittaria subulata and Alternanthera reineckii enriching Verrucomicrobiota.

## Abstract

Maintaining stable conditions in small, unfiltered aquaria for betta fish is a significant challenge. This study investigated whether adding aquatic plants could serve as a natural biofilter and provide environmental enrichment to improve the aquatic environment and fish welfare. Over 25 days, aquaria containing aquatic plants, such as Sagittaria subulata, Alternanthera reineckii, and Wolffia globosa, compared to a plant-free control, were monitored. We found that the aquatic plants, particularly S. subulata, effectively reduced ammonia nitrogen. Furthermore, fish in aquaria planted with S. subulata displayed the longest average active swimming time and fewer negative behaviors. The plants also fostered a more diverse water microbial community at the end of the experiment. These results demonstrate that adding aquatic plants tends to improve the water quality and animal welfare in newly established betta fish tanks.

Maintaining water quality and fish well-being in newly established, small, unfiltered betta (Betta splendens) aquaria is a significant challenge. To improve betta fish breeding and welfare, this study set up four groups: the Sagittaria subulata (S.su) group, the Alternanthera reineckii (A.re) group, the Wolffia globosa (W.gl) 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 S.su 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 (p < 0.05). The behavioral analysis revealed that, during the 25-day randomized monitoring period, bettas in the S.su 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 (p < 0.05). Additionally, the S.su and W.gl 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 W.gl group had the highest microbial diversity, and the A.re and S.su 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, S. subulata demonstrates the greatest benefits under the experimental conditions, making it a more suitable choice for this experiment.