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     One of the most interesting and devastating dramas to occur within our lifetimes is certainly the story of East Africa's great Lake Victoria. Scientists were bewildered at the astonishing rate of extinction happening in front of their eyes. Little hope was given for the future of the lake's endemic cichlids comprised entirely of haplochromines. Now over 20 years since we learned of the horror the Nile perch played in the destruction of Lake Victoria's fragile ecosystem we have begun to see changes that we thought would have taken thousands of years to occur. Several species of the cichlids found in Lake Victoria are making a comeback; as their population rises up they bring along a new twist to the story - they have evolved into morphologically faster swimmers and have begun to exploit food sources unknown to the species in question. Species are adapting to habitats previously known for them to occur in. To add to this excitement, new unknown species seem to be popping up out of the blue; are these hybrids, undiscovered cichlids, or totally new? To put it as un-technical as possible, evolution is occurring right before our eyes at an unheard of pace.

    You may be thinking, "Wait a second, what the heck are you talking about?" First let me explain as simply as possible what occurred in Africa's great Lake Victoria. Here we go: several non-native species introductions have occurred within Lake Victoria to "improve" the lake's fisheries over the last half a century. The most destructive of these introductions occurred around 1965 in Uganda after the Ugandan government introduced several hundred Nile perch into Lake Victoria. In the early 1980's a team of scientists "discovered" that the Nile perch was wreaking havoc consuming the lake's native fish stock. Species began to disappear, micro and macro ecosystems crashed and the lake was surely dying at a fast pace. Along with the Nile perch, run-off, pollution, more exotic species introductions, and overfishing were depriving the lake of the surviving species. Entire groups of cichlids went extinct, and the catastrophe was stated to be the largest mass extinction since the dinosaurs.

    Populations of at least two trophic groups have been observed to enjoy a slight increase of their populations along sub-littoral water located in the Mwanza Gulf. While pelagic zooplanktivores have always held on tight during the Nile perch uproar, their populations are showing healthy growth. At least one trophic group thought to have disappeared from the region is making a strong comeback. I am talking about the demersal detrivores. While these two trophic groups are starting to increase quite well, let us not forget that this area of the lake was composed of over ten separate groups! Species from other groups are declining rapidly and a huge amount of species are now thought to be extinct.

    It is interesting to note that several species thought to be extinct within Lake Victoria have resurfaced in a new habitat, suggesting that vulnerable species, due to Nile perch predation, can adapt and find refuge within a new habitat, until now unexplored by the species. One prime example of this disappearing act, only to reappear a few years later, is the pelagic zooplanktivore, Haplochromis tanaos. Before the Nile perch population exploded, H. tanaos, a species being reproduced in small numbers within captivity, was restricted to a littoral sand bottom habitat. After years of rapid reduction of the populations, the species disappeared from the sand bottoms by 1987. Amazingly enough in 1993 scientists found this species in fair numbers over littoral and sub-littoral mud bottom habitats. Why such a change in habitat? It is thought that this change has resulted in adaptation in order to elude the gigantic Nile perch.

    An extremely colorful oral shelling molluscivore, Haplochromis (Paralabidochromis) plagidon (also being bred in small numbers within captivity) has been observed to express this adaptation to a similar degree except the species has only declined drastically and has not gone extinct in its original littoral sand bottomed habitat located along Mwanza Gulf's east side. At the same time this species populations along the east side were being weakened, H. (P.) plagidon managed to establish healthy populations along the west shores of the Mwanza Gulf located over littoral and sub-littoral sand bottom habitats. This species has never known to occur in these areas before, suggesting possible habitat migration.

    This information gives many scientists, familiar with the situation, hope that deepwater species may be residing in refuge from non-native predation by shifting their populations into "new" habitats among the reeds or in the rocks along the lake's littoral shores. Another possibility that has been well argued is for deepwater species being able to find refuge in the lake's lower oxygen deprived waters. The Nile perch is unable to enter these areas due to being un-adapted to the low levels of oxygen provided for such a large fish. It seems anything is a possibility at this point. I guess we will just have to wait and see what is caught along the shores before we can access this situation in its entirety.

    One of the most impressive changes in Lake Victoria's cichlids is the drastic change in morphological characteristics. We are now beginning to see familiar species become slimmer and more elongated. One theory to explain this scientifically interesting rapid evolution lays the question right on top of one of the lake's major problems. The Nile perch! So why would a species become slimmer and more elongated in the presence of such a predator? How about the skills of locomotion? A slimmer more elongated body shape would decrease the water pressure on the cichlid and would increase its overall speed. This seems to be the most reasonable answer to this stunning discovery. They are changing to flee Nile perch predation. Never has science seen such an important detail relating to the survival of a species happen so fast, and to top it off, right before our eyes!

    Why we can only currently hypothesize the exact reason why these changes are becoming commonplace in Lake Victoria's environment, there are several possibilities. One of them is species hybridization; another is natural selection of the fittest within a given species. Likely both are coming into play. With the lake's water visibility at an all time low due to pollution and various other elements, it has made hybridization quite likely. Due to recent experiments under captive conditions in a lab located in the Netherlands, we now know that colors of Lake Victoria's cichlids play the key role of identification within a species. For proper selection to occur involving the same species, high water visibility is gravely needed. Without it, females have been shown to show no preference between spawning with members of the same species or those of a different species. In other words, under decreased water visibility, females have no idea if they are spawning with a different species. This data provided under captive conditions is also showing true within the lake. Members of the Haplochromine Ecological Survey Team (H.E.S.T.) have witnessed several possible hybrids being collected within the lake's various habitats. Natural Selection has certainly become a reason for these changes, with only the cichlids able to escape predation passing on their genes to their subsequent offspring.

    Lake Victoria will continue to amaze us with each discovery as we understand the delicate but adaptive balance that entwines these highly evolved cichlids. Their beauty will keep us coming back to the lake to monitor and observe their behavior for years and hopefully decades to come. While the average hobbyists will doubtfully visit Lake Victoria in Africa, they can help scientists around the world understand these rare haplochromines by partaking in responsible breeding programs to ensure these cichlids' numbers will thrive, at least within captivity.

References and Further Reading:
Witte, F., K.D.N. Barel, and M.J.P. van Oijen. 1997. Intraspecific variation of haplochromine cichlids from Lake Victoria and its taxonomical implications. South African Journal of Science, 93:585-594.

Oijen van, M.J.P., F. Witte. 1996. Taxonomical and ecological description of a species complex of zooplanktivorous and insectivorous cichlids from Lake Victoria. Zoologische Verhandelingen Leiden 302:1-56.

Seehausen, O. 1996. Lake Victoria Rock Cichlids. Taxonomy, ecology, and distribution. Verduijn Cichlids, Zevenhuizen, Netherlands.