# Freshwater Fish Biodiversity Changes Before and After the Indrapuri Dam Construction in the Bihar Region

## TL;DR

Building the Indrapuri Dam in Bihar caused a major drop in freshwater fish diversity, but recent improvements in water quality are helping some species return.

## Contribution

This study reviews long-term changes in fish biodiversity before and after the Indrapuri Dam construction, highlighting recovery trends and water quality impacts.

## Key findings

- Fish biodiversity dropped from 95 species in 1957 to 25 in 2017, but increased to 41 by 2023.
- Cypriniformes and Siluriformes orders saw significant declines of 75% and 61%, respectively.
- Improved water parameters in recent years have led to the return of some fish species downstream.

## Abstract

Freshwater biodiversity suffers when dams are constructed. It is important to evaluate how these changes take place, to what level they impact. In this review, we summarized the effects of the Indrapuri Dam’s construction on fish biodiversity over the years on the basis of available studies. We compared the fish biodiversity study done in 1957 before it was built to the studies that were done several years after the dam was ready in 1968. Available information was categorized into five most relevant and other less relevant studies between 1957 and 2023. These studies indicate that fish biodiversity declined drastically after the dam construction. A total of 95 different species of fish lived in the Indrapuri Dam basin before the dam was made; however, only 25 species were noted in 2017 after the construction of the dam. Further, this number increased to 41 in 2023. Several fish species disappeared between 1957 and 2023, notably, those that prefer well-oxygenated and stream-like environments. Biodiversity kept decreasing post-construction for a very long time. The biggest representative order, Cypriniformes, reduced by 75%, followed by the order Siluriformes, which reduced by 61%. Possible reasons for this reduction in diversity could be changes in migratory routes of fishes, the requirement of fast-flowing water, the requirement of upstream movement for spawning, or the requirement of a specific substrate for breeding. Some new fish species showed up in 2014 but were never reported after that. Though many species couldn’t survive these disturbances, fish biodiversity in the dam area has now started improving. By 2023, 12 new fish species belonging to the families Bagridae, Erethistidae, Cichlidae, Cyprinidae, Osphronemidae, and Belonidae had established themselves downstream of the dam. To analyze the reasons for the changing biodiversity in this region, we also reviewed the available studies related to water parameters. Water parameters in the area have improved recently. Some fish species are settling back. If the water parameters continue to improve in line with the recent trend, it is anticipated that the fish biodiversity in the region will improve in the near future.