Gut content analysis of Nile tilapia in and around Ggaba landing site, Lake Victoria

Abstract

Nile tilapia is an omnivorous fish and its natural feed includes phytoplankton, aquatic plants zooplankton and arthropods. Nile tilapia can be found in rivers, reservoirs and other natural waters. The study was conducted on Nile tilapia obtained from Lake Victoria, at Ggaba landing site which is located in Makindye division, Kampala district, and it’s affected by pollution from human urban activities. Gut content analysis is important for providing information for monitoring and maintaining functional lake ecosystems. It provides insight into fish feeding patterns and quantitative assessment of food habits which promote fisheries management by availing a basis for understanding trophic interactions in aquatic food webs. Nile tilapia were purchased from fishers who harvested them using gill nets. The fish were weighed and the total length measured. The Nile tilapia were dissected and guts were obtained before being split open onto a clean petri dish. The contents in the guts were analyzed using the frequency of occurrence. The relative condition factor of Nile tilapia ranged from 1.61 to 2.26, with a mean value of 1.91 (± 0.179) SE) indicating a fair condition factor. The length-weight relationship showed a linear proportionality with a calculated R-value (0.868, p = 0.004) indicating a negative allometric growth, and the length-weight relationship described by the equation: log TW = -1.33 + 2.75 log TL. The analysis of contents in the guts of Nile tilapia from Lake Victoria showed Chlorophytes and Cyanophytes form the largest portion of Nile tilapia diet as evidenced by their 33.33% and 26.32% occurrences in the gut of Nile tilapia. The other food items consumed by Nile tilapia include; plant material and arthropods. Conclusively, the high frequency of occurrence of cyanophytes including Anaebanae and Microcytis could be the result of pollution of Lake Victoria by human urban activities. Proper management of Lake Victoria is essential for sustainable fish stock exploitation in the country and more research linking the stomach fullness and occurrence of feed items in each stomach should be conducted to determine the contribution of each feed on the performance of Nile tilapia from Lake Victoria.