Observations on the biology of Nile tilapia, Oreochromis niloticus L., in two Ugandan crater lakes

Abstract

In this study, we compare the diet, life history characters and abundance of Nile tilapia (Oreochromis niloticus) stocks between two crater lakes in western Uganda (Lake Nyamusingiri and Lake Kyasanduka) that differ in their history of fishing pressure. Both lakes support native fish communities, but also harbour populations of introduced O. niloticus. Lake Nyamusingiri was characterized by a higher relative and absolute abundance (CPUE) of haplochromine cichlids and a lower abundance of O. niloticus than in Lake Kyasanduka. In addition, the O. niloticus population in Lake Nyamusingiri exhibited a smaller mean size and a lower relative abundance of juveniles than in Lake Kyasanduka. These differences may reflect, at least in part, heavy exploitation of O. niloticus in this lake, as compared with Lake Kyasanduka where fishing was banned in 1988. In both lakes, the maximum size and size at maturity was small relative to other larger water bodies in the region. The Nile tilapia in both lakes were primarily herbivorous; with phytoplankton dominating the diet. In general, the condition of O. niloticus in the crater lakes was low relative to other larger lakes in the region. The low catch per unit effort of O. niloticus in Lake Nyamusingiri (7.8%) relative to Lake Kyasanduka (54.9%) suggests that overexploitation of the fishery is occurring, calling for careful monitoring and management of the system.

Anthropogenic impacts on the contextual morphological diversification and adaptation of Nile tilapia (Oreochromis niloticus, L. 1758) in East Africa

“…Condition factor K has been associated to other factors, including fish abundance and competition in ecosystems (Balirwa 1998;Bwanika et al 2004;Otieno et al 2013). For example, Balirwa (1998) reported that with declining fish populations in Lakes Kyoga and Victoria, less competition for food resources could have led to improvement of K values.…”

Assessing Sustainable Fishing Yields Using Length-based Analytical Models: A Case Study with Nile Tilapia in Lake Hawassa (Ethiopia)

“…Another common sign for the occurrence of overfishing is a reduction in the mean length of fishes in the catch [27]. Stunting or dwarfing of tilapia is a common phenomenon whenever there is high fishing pressure [39]. In line with this pattern, also the tilapia of Lake Hawassa is becoming stunted and matures at a smaller size.…”

“…Stunting or dwarfing of tilapia can also be a sign of overexploitation [8,27,39] in the southern fishery. Length at first sexual maturity of tilapia in Lake Hawassa is 18 cm [40].…”

Management Implications of the Response of Two Tilapiine Cichlids to Long-Term Changes in Lake Level, Allodiversity and Exploitation in an Equatorial Lake

“…In studies where the inundation of the margins of African lakes by flood waters has occurred, the combination of decaying submerged terrestrial vegetation and the increased fluvial input of nutrients has resulted in increased production of detritus, phytoplankton, periphyton and zooplankton (Weyl 2007), with phytoplankton production also enhanced by the decreased turbidity (Guenther and Bozelli 2004). In response to the inundation and increased food resources, production of the tilapia species increases (McKaye et al 1995;Bwanika et al 2004;Njiru et al 2004;Peterson et al 2004Peterson et al , 2005Britton et al 2009). Increased growth rate and recruitment success following flood events have also been generally observed in cichlid populations (Dudley 1975(Dudley , 1979De Silva 1985;Weyl 2007) and appears evident in Lake Naivasha (Britton and Harper 2008).…”