Escapes from aquaculture facilities in freshwater ecosystems; conservation concerns for Oreochromis tanganicae, an endemic species of Lake Tanganyika

Abstract

Introduction of farmed non-native fish strains into ecosystems outside their native range has raised global concerns. We investigate the presence of Oreochromis niloticus in the southernmost part of Lake Tanganyika. DNA was extracted from tissue samples and analysed using microsatellite DNA markers. We confirm the O. niloticus from the observed morphological features of the samples collected and the analysis using genetic markers. Although the species is native to the lake, it is unclear if the fish now being sampled are indigenous or escaped from aquaculture facilities 15–20 years ago. The genetic diversity was similar statistically, though higher in O. tanganicae, followed by wild O. niloticus and least in farmed O. niloticus. There was no evidence of hybridisation between O. niloticus and native O. tanganicae. We recommend a comprehensive investigation to ascertain the origin of the O. niloticus, which, though rare, is present in catches. Due to known introductions, conservation measures must be set up to protect the genetic purity of O. tanganicae since O. niloticus is known to hybridise with other Oreochromis species and it is not known whether the farmed non-native strain is capable to establish such hybridization more than the wild native strain.