Geographic distribution and identification of pathways of interactions of Tilapiine species between natural and aquaculture systems in upper Tana River Basin, Kenya

Abstract

Freshwater fish habitats are highly threatened, facing impacts from habitat degradation, overfishing, and the introduction of non-native invasive species. Tilapia fishes are at the center of freshwater fishes due to their essential in fisheries and aquaculture production and preferences. This study investigated the impacts of introduced tilapia species on close relative native tilapia species in the Upper Tana River in Central Kenya. Tilapia specimen were collected in 24 sampling sites, their body morphometric data obtained and then used to assess hybridization rate between introduced and native tilapia species and sites mapped for the tilapia distribution. A basic water quality parameters measured in all the sampling sites including rivers, dams and fish ponds. Also, a social survey was undertaken to evaluate the human activities triggering the fish interaction. The results showed the presence of non-native tilapia in the upper catchment of the Tana River: Nile tilapia (Oreochromis nioticus), Redbreast tilapia (Coptodon zilli), Redbelly tilapia (Coptodon rendalli), and Mosambique tilapia (Oreochromis mossambicus) alongside native species, Sabaki tilapia (Oreochromis spilurus). The Nile tilapia had a wider survival range compared to normal ranges, especially temperature (17-31°C). The aquaculture (demand and preference of tilapia) was the main driver of tilapia introduction. It was concluded that widespread stocking of non-native tilapia strains will likely harm the persistence of natural strains, through ecological competition and hybridization. Zonation of aquaculture activities; proper implementation of the fisheries acts and policies and genetic analysis to provide evidence of tilapia hybridization were recommended.