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| Nile Perch |
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| Cichlids! Issue: Life will cease to exist in Lake Victoria, if no preventative action is taken. |
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| Cichlids Context: The Nile Perch was introduced to Lake Victoria in the 1950s. It is a predator that feeds on fish (including its own species), crustaceans, and insects. It is in the top 100 worst invasive species list. It is respinsible for the extinction, or near extinction of several hundred species native to the lake. Its diet consisted mainly of the cichlids, but due to declining numbers, now has to eat minnows and shrimp. The Nile Perch has now been over fished, and any remaining fish are running out of food. This gives a chance for the cichlids to repopulate. However, the ones that repopulate are the ones whose diet consists mainly of algae, due to a lack of carnivorous food sources. The biodiversity of the cichlids was accomplished in only 12,000 years. Many studies were being conducted about the cichlids, when they became endangered.  This is a problem to us because this fish is a top-chain level predator. We can see what it is capable of doing to a foreign ecosystem, yet not much is being done. This fishing industry of the Perch has replaced the fishing of cichlids, which were initially sun-dried before being shipped off. The perch requires smoking in order to prevent spoiling because of its high fat content. This requires the use of fire wood in an area that faces deforestation and soil erosion. Also, the nets required to catch a perch are not made locally, and importation costs a lot. This industry was supposed to increase the economy, but has only brought the people farther into poverty.  The algar biomass of the lake has increased exponentially. This has caused the oxygen levels to become supersaturated near the surface, becoming less fit for many types of life. It has also caused the water to become colder in the shallower areas, due to lack of circulation, where the juvenile fish stay. The increase in algae can be attributed to the soot, ash, and waste being disposed of into the lake, since the introduction of the perch. Most of the nutrients required for repopulation are found at the very bottom of the lake, which is unaccessible to many fish. Also, the influent rivers do not send enough nutrients for a lake of this magnitude.The fertility of the lake is dependant on the decomposition rate of the dead fish, since the algae does not deteriorate at a fast enough speed.The population of plankton has increased due to the feeding needs of the cichlids. This has created a parallel cycle that goes back and forth between the plankton and cichlids. The introduction of the Perch killed the cichlids that were responsible for regulating the algae levels of the lake. This helped cause the extinction of many cichlids due to the high oxygen levels.  The British saw the 500 species of cichlids as an oppourtunity to make money. They were too boney to eat, and the only two species of tilapia did not produce as much income as they would have liked.They needed a lake as large as Lake Victoria, and a predator in order to increase the value of the cichlid stocks.  Some reasons for the introduction of the perch
Before the introduction of the perch, more species of tilapia were introduced. The main difference was that the tilapia were vegetative fish. The perch was introduced three times in the lake, in 54', 63' and 64'. The introduction of the tilapia did not go well. They were not able to establish themselves for two decades. In the early 1960's, the rainfall rose considerably and increased the lake's volume and shoreline. This created shallower areas for the tilapia to spawn. The cichlids were once 80% of the lake's biomass. Now, they are only 1%  Those fish need to occupy something...  |
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| cichlid In 20 years, the cichlids have managed to adapt to the water's conditions. The gills of the fish have increased by 64%, along with the head, eyes and cheek bones, though the head has gotten smaller. The solution would be to give the lake a rest and let nature do its job. So far, the cichlids have been growing in numbers and have even adapted. Sadly, this lake will probably see a cycle of development, and exploitation. Either someone will introduce a new species, bacteria or plant into the lake in order to "help" the lake return to its previous state, or the fish will be overfished and biomass lost. There is no way they will leave the lake alone. All we can do is hope that the industry does not kill the lake entirely. |
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