Fish assemblage patterns influenced by nutrient levels and thermal effluent from power plants in the lower reaches of Berung and Wadas Rivers, Serang Regency, Banten, Indonesia

The downstream of the Berung and Wadas Rivers in Serang Regency, Banten Province, Indonesia, possesses economically significant fishery resources. However, these waters face environmental threats, notably thermal effluent from a Steam Power Plant. This study aimed to analyze fish species diversity and habitat conditions by examining the relationship between fish assemblages and key physicochemical factors, specifically temperature and nutrient levels. The study was conducted in January 2020 at six sampling stations representing riverine, estuarine, and marine zones. Fish samples were collected using gillnets, while physicochemical parameters (including temperature, nutrients, DO, salinity, and pH) were measured concurrently. Fish diversity was evaluated using the Shannon index, and the relationship between fish assemblages and environmental variables was analyzed using Principal Component Analysis (PCA) and Canonical Correspondence Analysis (CCA). A total of 63 individual fishes, comprising 11 species from 10 families, were recorded. The squaretail mullet ( Ellochelon vaigiensis ) was the dominant species (67%). Fish diversity varied significantly across stations. Stations 1, 2, and 6, located in productive estuarine areas, exhibited higher fish diversity. Conversely, Station 5, situated near the power plant's thermal discharge, recorded elevated temperatures (37.5°C) and low fish diversity, indicating negative impacts from thermal pollution. The findings confirm that the thermal effluent acts as a pollutant, creating environmental instability for the aquatic biota. Therefore, improved waste management strategies are necessary to mitigate the ecological impacts in this area.