The Nile perch (Lates niloticus) is a species of freshwater fish in family Latidae of order Perciformes. It is widespread throughout much of the Afrotropic ecozone, being native to the Congo, Nile, Senegal, Niger, and Lake Chad, Volta, Lake Turkana, and other river basins. It also occurs in the brackish waters of Lake Maryut in Egypt. Originally described as Labrus niloticus, among the marine wrasses, the species has also been referred to as Centropomus niloticus. Common names include African snook, Victoria perch (a misleading trade name, as the species is not native to Lake Victoria), and a large number of local names in various African languages, such as the Luo name mbuta or mputa. In Tanzania, it is called sangara, sankara or chenku. In Francophone African countries, it is known as capitaine and in Egypt/Sudan as am'kal. Its name in the Hausa language is giwan ruwa, meaning "water elephant".
Lates niloticus is silver in colour with a blue tinge. It has distinctive dark-black eyes, with a bright-yellow outer ring. One of the largest freshwater fish, it reaches a maximum length of nearly 2 m (more than 6 ft), weighing up to 200 kg (440 lb). Mature fish average 121–137 cm (48–54 in), although many fish are caught before they can grow this large.
Adult Nile perch occupy all habitats of a lake with sufficient oxygen concentrations, while juveniles are restricted to shallow or nearshore environments. A fierce predator that dominates its surroundings, the Nile perch feeds on fish (including its own species), crustaceans, and insects; the juveniles also feed on zooplankton. Nile perch use schooling as a mechanism to protect them from other predators.
Nile perch have been introduced to many other lakes in Africa, including Lake Victoria (see below) and the artificial Lake Nasser. The IUCN's (World Conservation Union) Invasive Species Specialist Group considers L. niloticus one of the world's 100 worst invasive species.
The state of Queensland in Australia levies heavy fines on anyone found in possession of a living Nile perch, since it competes directly with the native barramundi, which is similar and grows to 1.8m long while the Nile Perch grows to 2m long.
Lake Victoria introduction
The introduction of this species to Lake Victoria is one of the most cited examples of the negative effects alien species can have on ecosystems.
The Nile perch was introduced to Lake Victoria in East Africa in the 1950s, and has since been fished commercially. It is attributed with causing the extinction or near-extinction of several hundred native species, with some populations fluctuating with commercial fishing and the actual Nile perch stocks. The Nile perch's initially fed on native cichlids, but with decreasing availability of this prey, it now consumes mainly small shrimp and minnows.
The fish's introduction to Lake Victoria was ecologically negative, and lead to the establishment of large fishing companies. In 2003, Nile perch sales to the EU reached 169 million euros. Sport-fishing in the region of Uganda and Tanzania provided additional income for tourism. The long-term outlook is unclear, as overfishing is reducing L. niloticus populations.
The alteration of the native ecosystem had disruptive socioeconomic effects on local communities bordering the lake. Large-scale fishing operations, while earning millions of dollars from their exported L. niloticus catch, have displaced many local people from their traditional occupations in the fishing trade and brought them into the cash economy or - before the establishment of export-oriented fisheries - turned them into economic refugees. At least initially[verification needed], nets strong enough to hold adult Nile perch could not be manufactured locally and had to be imported for a high price.
The introduction of Nile perch has also had additional ecological effects on shore. Native cichlids were traditionally sun-dried, but Nile perch have a higher fat content than cichlids, so instead need to be smoked to avoid spoiling. This has led to an increased demand for firewood in a region already hard-hit by deforestation, soil erosion, and desertification.
The Academy Award-nominated documentary Darwin's Nightmare by Hubert Sauper (a French-Austrian-Belgian production, 2004) deals with the damage that has been caused by Nile Perch introduction, including the import of weapons and ammunition in cargo planes from Europe that then export Nile perch, exacerbating conflict and misery in the surrounding regions. However, to those who consider the introduction of Nile perch beneficial Darwin's Nightmare is controversial. They accuse the documentary of implying fictitious causalities. Even critics of the introduction have not praised the focus on spectacular but only loosely correlated recent issues, to the neglect of the actual ecologic and economic upheaval caused by L. niloticus proliferation in Lake Victoria.
Regardless of whether it is considered positive or negative, the trophic web of Lake Victoria appears to have been drastically impoverished by the introduction of this novel near-top-level predator. While the lake ecosystem seems to be moving towards a new equilibrium, neither its former state nor the state of fisheries on Lake Victoria can ever easily be brought back.
On Lake Victoria, the only (small) trawlers present belong to research institutes. Small-scale fishing boats are propelled mostly by sails, and paddles are used on the smallest boats. However the number of boats propelled by outboard engines is on the rise, denoting a greater capital intensity of the local Nile perch fishery (see Beuving, 2013). One to three fishermen use a boat. The fish is caught with mainly gill nets and handlines and sometimes (short) longlines. Those caught by gill net are usually dead when the nets are lifted. The fish are kept in the boat without protection or ice and taken to landing sites, mostly beaches, where they are weighed and purchased by company buyers using insulated boats or vans with ice, or the fish is bought by local women.
The fishery also generates indirect employment for additional multitudes of fish processors, transporters, factory employees, and others. All along the lakeshore, 'boom towns' have developed in response to the demands of fishing crews with money to spend from a day's fishing.[Note 1] These towns resemble shanties, and have little in the way of services. Of the 1,433 landing sites identified in the 2004 frame survey, just 20% had communal lavatory facilities, 4% were served by electricity, and 6% were served by a potable water supply.
Nile perch bought at the beach by women is usually cut into large pieces and smoke-dried for sale in distant places. Those bought by company buyers - usually company drivers - are placed on ice in an insulated company van or collection boat. After one to three days the van or boat will take the fish to a processing plant where the fish is filleted and the fillets are exported either by air if fresh or by boat if frozen. Local people around Lake Victoria prefer to eat tilapia rather than Nile perch, but in West Africa, Sudan, and Egypt, as well as in Israel, it is highly appreciated. In the 1990s, the value of Nile perch exports from Lake Victoria reached almost US$ 300 million per year.
The yield of fillets from a whole ungutted fish is about 30%. The remainder is head, skin, guts, bones and fins plus meat attached to the filleting frame. The frames used to be smoke-dried for local consumption, while heads and skins were used as fuel under frying pans to collect oil from the guts. Now, the companies process the filleting waste to fish meal. However, the swim bladder is dried and sold to traders for export to Southeast Asia where they are used as food.
- See for an anthropological study of these towns, called village landings, Beuving (2010).
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|Wikimedia Commons has media related to Lates niloticus.|
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