Imagine a 6 foot fish species introduced by man into a lake with no fish over 10 inches. What would be the effects? Even though it seems unfathomable, it happened 50 years ago in Lake Victoria, Africa. The fish was the Nile Perch (Lates Niloticus). The end result was the largest extinction of vertebraes in recorded history, with over 250 species of fish being lost, leading to the collapse of the third largest lake in the world, which 30 million people depend on for food and their economy. The introduction of the Nile Perch into Lake Victoria has caused tremendous economic and ecological chaos, and continues to have effects on not only that lake, but surrounding bodies of water as well.
In the early 1900s, the British introduced technologically advanced fishing techniques to the African colonies they owned for economic reasons (being able to tax the African people more for instance). Soon, Lake Victoria became over-fished, and their big food fish, Oreochromids, were led to extinction. So they introduced a foreign fish into the lake, to get fishing stocks back up. It was the Nile Tilipia. It was a planktonivore, so its presence did not greatly affect the fish populations of the lake. Since that went well, in 1954 they introduced another foreign fish, the Nile Perch, despite repeated ecological warnings.
The Nile Perch grows 6 feet long, and can weigh 70 kilograms. They are very prolific fish as well. The largest fish in the lake before that introduction were the Haplochromines (a large group of fish from the Cichlidae family) which composed almost all of the higher life in the lake. The largest Haplochromine grows 10 inches, while most average out at around 5 inches. So a piscovorous fish (one that eats other fish) that grows more than six times the size of any other fish in the lake, was introduced; and these fish have no natural predators.
For many years, nothing appeared to be wrong. Then in 1978, the populations of the lake suddenly started to change. The Haplochromines went from composing 80% of the lake, to less than 2% within 5 years. The Nile Perch population went from 2% of the lake, to 80% within that time. Noone knows why it took that long for that effect to occur.
With such a low population of Haplochromines for them to eat, the Perches have started cannibalizing each other. This means that soon, even they may become extinct in that lake, and with all the other factors taking place, the lake will become completely devoid of fish. Fisheries that used to bring in 10,000 fish at a time, bring in about 10 now on average.
Despite the Nile Perch’s desire to consume every fish in the lake, it also supplements its diet with other foods. Meaning that if the fish survived predation by the Nile Perch, they would still die of starvation due to the corresponding shortage of food.
The Nile Perch did boost the economy temporarily, as it was a big food fish and caused fisheries to develop along the shorelines. However, as the fisheries catch of fish depleted over time, they could not afford to manage and remove the waste they produced, so it was dumped into the lake. This caused massive algae blooms due to the nutrients, and promoted certain plant species, like water hyacinths, to out-compete others. The algae absorbs large amounts of Oxygen from the water, leading to very low levels of Oxygen in some places, causing them to be inhabitable. It also leads to much higher populations of plankton in the water, and without the aid of the natural planktonivores (which the Nile Perch consumed) has lead to another misbalance in the lake. The Plankton also consume Oxygen. Consequently, there are not sufficient Oxygen levels for life to persist below 30 meters in the lake. The increased nutrients, and anaerobic areas on the bottom of the lake have caused toxic compounds to develop as well. The fish have been forced from the bottom of the lake to the top, where the Nile Perch awaits to eat them.
The higher levels of nutrients have also indirectly caused the water to become cloudy. This leads to light not being able to penetrate into lower levels, causing most algae growth, which is an important food for the native fish, to occur in the shallow wide-open spaces of the lake. If the herbivorous fish want food, they have to come out into the open to get it, where the Nile Perch again waits to prey upon them.
The cloudy water has caused a more serious concern though. Haplochromines base much of their mate selection on color. Many times two completely different species can only be told apart by their coloration, which can be very slight. With the water cloudy, the fish cannot tell with certainty if they are mating with their own species, or a different one. This causes hybridizing, and the hybrids are many times sterile. Thus, while the fish are reproducing, the next generation may not be able to, further leading to the dying off of the fish populations in the lake.
With the fish population hardly existing in Lake Victoria anymore, and with that lake being the center of economic activity for that large area, the people are starving and cannot support themselves. The fisherman go out and work all day long, and come back with hardly enough food for one, let alone a family. In addition, Lake Malawi (another very large African lake) is now under pressure because of this, and a similar fate will await that lake as well, unless something is done. The people of Lake Malawi will not be able to handle a loss of fish in their lake, as that is the only thing that sustains the people. The largest lake in Africa, Lake Tanganyika, seems unaffected as of now though.
The proposed solution to help the countries that depend on Lake Victoria is to introduce another foreign fish into the lake, and develop an artificial ecosystem. This may have unforeseen effects.
The problem of non-native fish species being introduced into bodies of water is very present in the United States as well. Many African fish are being found breeding in both Florida and Texas. Many of the ones found are classified as Mbuna, and they’re the most highly evolved freshwater fish group. They are already out-competing the native fish, despite not having time to adapt to those waters. Most are 4.5 inch fish, but are so aggressive they can kill fish up to 3 feet long, so they have only a small number of natural predators. Furthermore, they have highly sophisticated means of raising and looking after their fry, which means more of their offspring survive to reproduce. Little can be done, as they hide among the rocks and eat the algae that grows on them, and are too intelligent to come out in the open and bite a fishing rod. In fact, they monitor the behavior of other animals around them, to determine if it is safe for them to come out. Being deep in the water, among the rocks, birds cannot limit their populations either. No proposed solution has been given on how to get them out of there, but without a solution, soon Florida and Texas will have more African fish than many of the African rivers.
The introduction of non-native species of fish into an ecosystem throws it off balance. The introduction of the Nile Perch into Lake Victoria caused the largest extinction of vertebrae animals since recorded history, and the collapse of that huge lake. Furthermore, it has caused economic chaos for the millions of local people, who are unable to obtain food now. A present-day holocaust that people are ignorant of. The effects are also spreading to Lake Malawi, and similar occurrences are becoming popular in Florida and Texas. Without brilliant ecologists, many more ecosystems will collapse.