Cascading effects of introduced Nile perch (Lates niloticus) on the foraging ecology of Nile tilapia (Oreochromis niloticus)

Abstract

-Nile tilapia (Oreochromis niloticus L.) is the dominant of the introduced tilapiines in many East African lakes and has flourished in the presence of introduced Nile perch (Lates niloticus L.). We explored the hypothesis that O. niloticus exhibits increased omnivory in response to a decline in abundance of haplochromine cichlids. First, we quantified variation in habitat use and diet of O. niloticus in Lake Nabugabo, Uganda. Second, we compared the diet of O. niloticus in lakes with (Nabugabo, Victoria) and without (Mburo, Wamala, Nyamusingiri, Kyasanduka) introduced Nile perch. In Lake Nabugabo, a higher level of phytoplanktivory was observed in small juveniles than in larger fish and in wetland ecotone areas where haplochromines were most abundant. An omnivorous diet dominated by detritus and invertebrates was recorded for O. niloticus in lakes Nabugabo and Victoria, while a predominantly herbivorous diet was characteristic of O. niloticus in lakes without Nile perch. Availability of a broad food base in lakes where inshore insectivores have been reduced may explain the increased omnivory recorded in lakes Nabugabo and Victoria.

Zooplankton capturing by Nile Tilapia, Oreochromis niloticus (Teleostei: Cichlidae) throughout post-larval development

“…According to several studies (GROVER et al 1989, UFODIKE & WADA 1991, ROCHA LOURES et al 2001, BWANIKA et al 2006, the percentage of zooplankton ingested decreases in the diet of species of Oreochromis, as fry develop into adults; it becomes constant, which was also observed in this study. A preference for zooplankton and diatoms to artificial food was observed during the first stages of Nile tilapia larvae (UFODIKE & WADA 1991).…”

“…In the initial stages of the development, some tilapia species prefer plankton (GROVER et al 1989, UFODIKE & WADA 1991 and this item is present in significant concentrations in the stomach of O. niloticus fry and adults (ROCHA LOURES et al 2001, BWANIKA et al 2006. The gill rakers of the Nile tilapia may be long and numerous, a characteristic of plankton-feeding species, or few and short, which characterizes on omnivorous diet (CÂMARA & CHELLAPPA 1996, BEYRUTH et al 2004, ZAYED & MOHAMED 2004.…”

Polychlorinated biphenyls and hexachlorocyclohexanes in sediments and fish species from the Napoleon Gulf of Lake Victoria, Uganda

“…The large variability observed in the data could be attributed to differences in feeding habits and trophic levels. While O. niloticus is a filter-eating fish species feeding mainly on phytoplankton and zooplankton, L. niloticus have predatory feeding behaviors and prefer a diet of live fish (Bwanika et al, 2006;Semyalo et al, 2011). The concentrations of the individual PCB congeners in L. niloticus at station A were statistically greater (p b 0.05) compared to other sites.…”

Biological invasions in the aquatic ecosystems of Europe as a threat to biodiversity

“…An excellent example is The Lake Victoria situation, connected with introduction of Nile perch Lates niloticus in 1954. As a result of predator activity, within a decade over 200 endemic fish species have disappeared forever out of the lake (Barel et al 1985;Craig 1991) and the ecosystem of the lake has radically changed (Bwanika et al 2006).…”