A review of the populations of tilapiine species in lakes Victoria and Naivasha, East Africa

Abstract

This paper discusses the status of tilapiine species both native and those introduced into Lakes Victoria and Naivasha. In Lake Victoria, Oreochromis niloticus, O. leucosticus, Coptodon zillii and Coptodon rendalii were introduced. Establishment of non-native species was associated with declines in the populations of the native O. esculentus and O. variabilis. Oreochromis niloticus dominates the commercial fishery, but populations of the other introduced species persist. Predation by Nile perch (Lates niloticus), overfishing, lake pollution and eutrophication have impacted negatively on the fish stocks. In Lake Naivasha, O. niloticus, C. zillii and O. esculentus were introduced. These species have also declined in catches due to the deteriorating lake conditions and effects of overfishing. Oreochromis leucostictus and O. niloticus dominate fishery catches, whereas C. zillii is rarely caught. The biological and population parameters of the tilapiines have shown great variations over time. O. niloticus and O. leucosticus attain early maturation. These changes are discussed as adaptive characteristics in response to intense fishing and changing ecological conditions. This therefore, calls for a need to improve on the management measures applicable in the two lake ecosystems, such as fishing effort control, pollution control and protecting the surrounding wetland from degradation.

A comprehensive review of invasion and ecological impacts of introduced common carp (Cyprinus carpio) in Lake Naivasha, Kenya

“…Establishing a self-sustaining population requires the non-native species to adapt to the new environment, with regard to the food resources and the abiotic and biotic conditions (Yongo et al, 2021).…”

“…Because the existence of a degraded habitat is known to promote carp invasion (Marvier et al, 2004), their success in Lake Naivasha could be a result of the lake`s degraded state (Njiru et al, 2017). The Lake Naivasha ecosystem is degraded as a consequence of swamp clearance, overexploitation, pollution and eutrophication (Hickley et al, 2015;Yongo et al, 2021). These threats might have resulted in loss of biodiversity, resulting in freeing up habitats for carp to exploit.…”

“…O. niloticus is highly invasive and has invaded the natural waters of many countries (Canonico et al, 2005;Grammer et al, 2012). The invasive success of O. niloticus in new habitats has been attributed to its ability to tolerate a wide range of environmental conditions, flexible habitat requirements, reproductive strategies, fast growth rate and omnivorous feeding habits (Canonico et al, 2005;Martin et al, 2010;Yongo et al, 2021). Blue-spotted tilapia (Oreochromis leucostictus) was introduced into Lake Naivasha in 1956 from ponds near Lake Victoria (Hickley & Harper, 2002).…”

“…It was first recorded in the lake in 2000 (Ojuok et al, 2007), together with its two subspecies of; Mirror carp (C. carpio specularis) and Leather carp (C. carpio coiaceus). Carp quickly became established in the lake, providing a commercial fishery and dominating the fish catches (Oyugi et al, 2011;Yongo et al, 2021). Being a highly invasive fish, carp dominance has presented high levels of concern and uncertainties on the Lake Naivasha ecology and fisheries.…”

Some biological aspects of the Silurid Catfish, Bagrus docmak (Forksskal, 1775) in Lake Victoria, Kenya

“…Many of these native species suffered severe declines because of predation by Lates niloticus, hybridization and competition with O. niloticus, and increased fishing pressure (Njiru et al, 2005;. Consequently, the lake's ecosystem has been severely affected by human activities and environmental changes, including the introduction of exotic species, invasion of water hyacinth, climate change, overexploitation, pollution and eutrophication (Yongo et al, 2021).…”