Influence of cage fish farming on water quality: The case of Tende bay, Lake Victoria, Uganda.

Abstract

The expansion of cage fish farming in Lake Victoria has raised concerns about its potential impacts on water quality and aquatic ecosystems. This study was conducted in Tende Bay from August to October 2023. Its objectives were to examine the relationship between cage fish farming and physicochemical parameters and to assess its effects on zooplankton diversity. A comparative study design was used, sampling four sites: two adjacent to cages (Sites 1 and 2, ~10 m from cages), one at 50 m distance, and an offshore control site 100 m from the shoreline. Water quality parameters measured included temperature, pH, dissolved oxygen (DO), and nutrient concentrations including nitrogen (N), phosphorus (P), and ammonia (NH₃) as well as chlorophyll levels. Statistical analysis (ANOVA, p < 0.05) indicated a significant increase in nutrient concentrations near the cages, with ammonia ranging from 0.03 to 0.57 mg/L and total phosphorus from 0.12 to 0.30 mg/L. These elevated nutrients, attributed to fish feces and feed waste, did not correspond with significant changes in chlorophyll levels across sites. Zooplankton diversity and composition differed significantly between cage sites and the offshore control (Shannon's index, p = 0.03), with rotifers showing higher abundance compared to Cladocera near cages. Despite nutrient increases, temperature (25.52–25.63°C), pH (7.84–9.15), and DO (3.62–4.81 mg/L) remained within acceptable ranges for aquatic life. Elevated NH₃ levels near cages (up to 0.57 mg/L) underline the need for continuous monitoring. While no consistent environmental degradation directly linked to cage farming was detected, the study recommends implementing regular water quality assessments and nutrient management strategies to ensure sustainable aquaculture practices in Lake Victoria."