Conceptual
Prior to the introduction of Lates niloticus, a balance between predators and prey species had evolved in Lake Victoria. Adaptations by both predators and prey had ensured that extermination of a species would not occur as a result of predation.
Since its introduction into Lake Victoria, Lates niloticus has become established as the dominant species and now makes up 50% of the fish landings from the lake. L. niloticus demonstrates a natural ontogenic change in diet but also has the capability of adjusting its feeding habits to take advantage of the most abundant food source. In Lake Victoria, as in other lakes where Lates has been introduced, many endemic prey-species have been almost elimimated and the Lates population is now largely cannibalistic.
1. Introduction
Lake Victoria try formed of the tectonic motions for the mid-Pleistocene (Fryer and you will Iles, 1972). New lake has actually a skin section of from the 68,800 kilometer dos , an optimum depth of 79m and you will a hateful breadth out-of 40m.
Of the estimated 200 species of fish occurring in Lake Victoria, about 3040% are piscivorous. The principal predatory fishes are Lates niloticus, Bagrus docmac, Clarias mossambicus, Schilbe mystus and some species of Haplochromis (sensu lato). Other predators in Lake Victoria include fish-eating birds, fish-eating snakes, crocodiles and otters. The lake supports important commercial fisheries based mainly on Oreochromis esculentus, Oreochromis variabilis, Bagrus docmac, Clarias mossambicus, Protopterus aethiopicus, Labeo victorianus, Schilbe mystus, the introduced Lates niloticus and Oreochromis niloticus.
Predator-prey interactions between the fish species in Lake Victoria are poorly documented. Descriptions of the relationship between various fish species and their prey have been made by Graham (1929), Corbet (1961), Okedi (1970), Hamblyn (1966) and Gee (1969). The relationship between Bagrus docmac and its prey species in Lake Victoria has been described by Chilvers and Gee (1974) and Ochieng’ (1982). Ogari (1984) described the relationship between Nile perch and its prey species in the Nyanza Gulf.
This paper covers a literature review on patterns of predation, including the major defences adopted by prey species, and includes a description of the relationship between Lates niloticus and its prey in the Nyanza Gulf of Lake Victoria.
2. Literature Review
Predators and prey have a wide spectrum of adaptive strategies to cope with their interactions. Predators are aided by morphological adaptations, which aid in pursuing, detecting and digesting prey. Most of the predatory fishes in Lake Victoria have streamlined bodies, large mouths and large eyes. Fryer (1965) described Lates niloticus as “swift” and Bagrus and Clarias as “lurkers”. Fryer and Iles (1972) reported that among members of the genus Haplochromis in Lake Victoria, the piscivorous species are larger in size (average maximum length 21.6cm). They described experiments to determine visual orientation for prey location using Haplochromis gowersi in Lake Victoria. Hamblyn (1966) performed similar experiments using Lates niloticus in Lake Albert. In both cases the predator seized and swallowed its prey whole, taking the prey in head first, however, H. gowersi chewed large prey before swallowing.
Victim fish also have morphological and you can behavioral changes getting securing on their own away from predators. Lowe-McConnell (1975) listed some systems seafood used to prevent predators, particularly education, modification from figure and you may along with, hands away from spines, dental incubation, guarding from eggs and you will younger an such like. Such changes don’t pay for complete protection but could serve to improve the danger of emergency (Popova, 1978).
Schooling of fish in Lake Victoria is common among such pelagic open-water species as Rastrionebola argentii, Alestes jacksoni and some Haplochromis species. Fryer and Iles (1972) explained that protection appears to be conferred by schooling because a predator presented with a single item of food receives only one set of stimuli which direct it to its prey, whereas confrontation with a school causes it to receive numerous conflicting stimuli which block the feeding response. They also mention that such an advantage will be greatest when the fishes are small and therefore vulnerable to predation. Hopson (1972 1975) observed leaping behaviour among small characins and Rastrionebola stellae in Lakes Chad and Turkana respectively. He concluded that such evasive movements were intended to assist the prey species escape predationparable behaviour has been observed among jak używać quiver the pelagic species of Lake Victoria (pers. obs.)