Ecological Assessment of Parasites and Environmental Drivers in Native Freshwater Fishes of Punatsangchhu River, Bhutan

Abstract

Fish parasites play a crucial role in the health and ecology of freshwater fishes; however, they are often overlooked. This study aims to determine the diversity and distribution of parasites in native freshwater fishes of Punatsangchhu and its tributary, Toebrongchhu, and examine their relationship with eco-hydrological parameters. A total of 44 fish specimens of Schizothorax richardsonii and Pseudecheneis sulcata were collected using cast net through systematic random sampling in winter month of December 2024. The specimens were dissected, and the parasites were examined under a stereomicroscope. Concurrently, water quality parameters were measured in the field. Two parasite genera, Rhabdochona spp. and Ergasilus spp., were identified. The low diversity (H’ = 0.05) may be attributed to low host diversity and data collection during winter. The parasite count showed strong positive correlations with fish weight (p < .001, ρ = 0.739) and length (p < .001, ρ = 0.773), suggesting increased susceptibility in older, larger fish. Logistic regression and the Mann-Whitney U test confirmed that infected fish were significantly larger and heavier. Parasite abundance also correlated positively with pH, temperature, TDS, EC, salinity, depth, and turbidity, indicating that elevated values of these parameters may impair fish immunity and increase the susceptibility to parasite infection. Principal Component Analysis revealed additional potential relationships between parasite prevalence and other eco-hydrological parameters. Furthermore, the spatial distribution of parasites indicated a higher prevalence in Punatsangchhu than in Toebrongchhu. This study provides baseline information on fish parasites in Punatsangchhu, which is essential for informing long-term aquatic biodiversity management and guiding fish health monitoring programs. The findings highlight the need for targeted parasite surveillance and adaptive management strategies to reduce disease risks and maintain healthy fish populations. Future research should incorporate seasonal, multi-species sampling and advanced diagnostic methods to support evidence-based conservation and sustainable aquatic biodiversity management.