Nile perch

Nile perch

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.

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 two metres (more than six feet), 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 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

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 since then it has 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. The long-term outlook is less clear, as overfishing is now reducing Lates 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 Lates 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 have 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 deliberately implying causalities that do not actually exist. Even among critics of the introduction, the focus on spectacular but only loosely correlated recent issues - the neglect of the actual ecologic and economic upheaval caused by L. niloticus proliferation in Lake Victoria - most of which happened in the 1960s and 1970s prior to introduction.

Regardless of opinion, it appears that the trophic web of Lake Victoria has been drastically altered through the introduction of this novel near-top-level predator. While the lake ecosystem is slowly finding to 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. Another income is the sportfishing tourism in the region of Uganda and Tanzania which aim to catch this fish.

See also

References

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