Nile perch

Nile perch
detail of a head
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Suborder:	Percoidei
Family:	Centropomidae
Genus:	Lates
Species:	L. niloticus
Binomial name
Lates niloticus (Linnaeus, 1758)

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, capitaine, 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 or sankara, or also chenku. In Francophone African countries it is known as "capitaine" and in Egypt/Sudan as am'kal.

Lates niloticus is silver in colour with a blue tinge. It has a distinctive dark-black eye, 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 Lates 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 but does not reach the same size as the Nile perch.

The species is of great commercial importance as a food fish. The Nile perch is also popular with sport anglers, as it attacks artificial fishing lures and is also raised in aquaculture.

Lake Victoria introduction

See also: Fishing on Lake Victoria

Forced perspective photograph of a Nile perch: The perch is not as large as it seems in this photograph.

The introduction of this species to Lake Victoria is one of the most commonly cited examples of the negative effects invasive 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, but as Nile perch stocks decrease due to commercial fishing, at least some of them are making a comeback. Initially, the Nile perch's diet consisted of native cichlids, but with decreasing availability of this prey, it now consumes mainly small shrimp and minnows.

The fish's introduction to Lake Victoria, while ecologically negative, has stimulated the establishment of large fishing companies there. In 2003, Nile perch earned 169 million euro in sales to the EU. Another income is the sportfishing tourism in the region of Uganda and Tanzania which aim to catch this fish. The long-term outlook is less clear, as overfishing is now reducing L. niloticus populations.

The alteration of the native ecosystem has also 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, 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. Darwin's Nightmare is highly controversial, however, to those who consider the introduction of Nile perch beneficial. They accuse the documentary of implying causalities that do not actually exist.^{[citation needed]} 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 opinion, the trophic web of Lake Victoria appears to have been drastically altered through the introduction of this novel near-top-level predator. While the lake ecosystem is slowly moving towards a new equilibrium, the former state of fisheries on Lake Victoria probably cannot be brought back, regardless of whether this is considered positive or negative

Fishery

The Nile perch fishery is small-scale only. With a high demand for Nile perch, the value of the fishery has risen considerably. Labour inflows into the fishery have increased along with growing demand. In 1983, there were an estimated 12,041 boats on the lake. By 2004, there were 51,712, and 153,066 fishermen. 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. 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. 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.

Food

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 fresh by air or frozen by boat. Local people around Lake Victoria prefer to eat tilapia, rather than Nile perch, but in West Africa and also in 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 300 million US$ per year.

The yield of fillets from a whole ungutted fish is about 30 percent. 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. Nowadays the companies process the filleting waste to fish meal. However, the swim bladder is dried and sold to traders for export to south-east Asia where they are used as food.

Nile perch meat has a high content of omega-3 fatty acids.

See also

• Nile tilapia - a different fish, which also belongs to the Perciformes, or perch-like fish

Further reading

• Beuving, J. J. 2010. "Playing pool along the shores of Lake Victoria. Fishermen, careers and capital accumulation in the Ugandan Nile perch business" Journal of the International African Institute 80 (2): 224-248.
• Pringle, R.M. 2005. "The origins of the Nile perch in Lake Victoria." BioScience 55:780-787.
• Masciarelli, Alex. “The rise and fall of the Nile Perch.” March 15, 2007. [1]
• Socio-economic effects of the evolution of Nile perch fisheries in Lake Victoria: a review. J. Eric Reynolds and D.F. Greboval, CIFA Technical paper 17, FAO 1988, ISBN 92-5-102742-0 (online version)
• M.L. Bianchini (1995). Species introductions in the aquatic environment: changes in biodiversity and economics of exploitation. Proc. World Fish. Congress (Athens, 1992), 3: 213-222.

External links

• Froese, Rainer and Pauly, Daniel, eds. (2004). "Lates niloticus" in FishBase. October 2004 version.
• "Lates niloticus". Integrated Taxonomic Information System. Retrieved 20 December 2004. 
• Lipton, David. "Lates niloticus: Information". Animal Diversity Web. Ann Arbor: University of Michigan Museum of Zoology, 2003.
• Snoeks, Jos. "Ecology of Lates niloticus". Global Invasive Species Database. Updated 22 September 2004.

• IUCN. "Alien Species Invade the Planet". Press release, 11 May 2001.