Freshwater Fish Diversity of Kodoor River, Kottayam, Kerala, South India

Abstract

The present study was conducted to gain a better understanding of the variety of freshwater fishes found in the Kodoor river. The Kodoor river has an abundance of indigenous fishery resources as well as a high level of biodiversity. The current study was carried out to identify the fish diversity of the Kodoor river in different layers(upstream, middle stream and down strean) and seasons(pre monsoon, monsoon and post monsoon). The study was conducted at different seasons (Post-monsoon, Monsoon, and Pre-monsoon) during the years 2021-2022. Fish for the study were collected from various locations along the Kodoor river by local fishermen. A total of 15 fish species representing nine families were documented. Among these, Cyprinus carpio, Dawkinsia filamentosa, and Horabagrus brachysoma were listed as Vulnerable, while the remaining species were of Least Concern. Family-wise analysis revealed the dominance of Cyprinidae, followed by Cichlidae and Channidae, with maximum abundance recorded during the monsoon season. Seasonal comparisons demonstrated that while the monsoon period supported the highest number of individuals (420), the post-monsoon season recorded greater diversity and evenness (Shannon index 2.081; Simpson’s diversity index 0.8631). This indicates that stable hydrological conditions after flooding events favor balanced species distribution. In contrast, the pre-monsoon period supported fewer individuals and comparatively lower diversity values. Spatial analysis across river stretches showed that the middle stream harbored the largest fish population (445 individuals), particularly dominated by Cyprinids, likely due to its favorable flow regimes and habitat heterogeneity. However, the downstream region exhibited the highest diversity indices (Shannon index 1.845; Simpson’s diversity index 0.812), suggesting that complex habitats such as pools and backwaters promote species coexistence. The upstream region supported moderate abundance and diversity. The presence of endemic and threatened species such as Horabagrus brachysoma underlines the ecological and conservation significance of the Kodoor River. Furthermore, the coexistence of both edible fishes (e.g., Wallago attu, Channa marulius, Etroplus suratensis) and ornamental species (e.g., Rasbora daniconius, Xenentodon cancila) highlights its socio-economic role in supporting fisheries and livelihood security for local communities.