Haplochromis vonlinnei (Cichlid)

One of 500 furu

Haplochromis vonlinnei is a probably extinct cichlid species from Lake Victoria in East Africa. The original scientific description of the species was published in 2008 by Dutch ichthyologist Martien J. P. Van Oijen based on five specimens caught between 1978 and 1980 in the southern part of Lake Victoria, in the Mwanza Gulf. These five specimens remain the only ones ever recorded, as the species has never been detected again. The International Union for Conservation of Nature IUCN lists Haplochromis vonlinnei as “critically endangered” but suspects the species may already be extinct.

H. vonlinnei was not the only cichlid (Cichlidae) endemic to Lake Victoria, and certainly not the only extinct cichlid or furu, as locals call the cichlids living in the lake. Scientists estimate that since the last desiccation of Lake Victoria approximately 12,000 years ago, an estimated 500 new cichlid species evolved there. Exactly how many species there were, no one can say, because just as Dutch zoologists were conducting an inventory, an ecological catastrophe radically transformed the fauna of Lake Victoria:

“Like the circles around a stone thrown into water, the Nile perch seems to spread in waves from the spot in Uganda where it was introduced. They are enormous predatory fish that eat their way through the lake like insatiable vacuum cleaners.”

This is how the Dutch biologist Tijs Goldschmidt describes the beginning of this catastrophe in Darwin’s Dreampond (1999), which started with the introduction of the Nile perch into Lake Victoria.

Haplochromis vonlinnei – fact sheet

alternative name	furu
scientific name	Haplochromis vonlinnei
original range	Lake Victoria (East Africa)
time of extinction	after 1980
causes of extinction	introduced Nile perch, overfishing, eutrophication, hybridization, water pollution
IUCN status	critically endangered (possibly extinct)

How the Nile perch became the Victoria perch

In the 1950s, British colonial officials thought it was a good idea to introduce Nile perch (Lates niloticus) into Lake Victoria. It should be noted that the Nile perch, which today is also commonly called the Victoria perch, is a predatory fish from the family of giant perches (Latidae). It normally occurs in rivers such as the Nile, Chari, Senegal, Volta, and Congo, as well as in some lakes and the Nile Delta. The Nile perch grows up to two meters long and weighs around 200 kilograms—a highly productive food fish. By releasing the enormous, prolific fish, it was expected that a commercially attractive food fish species could be cultivated. This was meant to boost the regional, export-oriented fishing industry, which it more or less did. However, the money did not end up with the destitute residents around Lake Victoria, but with the owners of the fishing vessels.

As a predatory fish, the Nile perch or Victoria perch brought not only advantages—it reproduced enormously fast in its new habitat and was a major contributor to the massive population decline or even extinction of many furu. Within 30 years, the Nile perch is said to have eradicated 400 different fish species in Lake Victoria, according to the documentary Darwin’s Nightmare (2004). Whether this number is close to the truth or completely exaggerated is impossible to say, especially since all the fish species living in Lake Victoria were never catalogued before the Nile perch was introduced. No one can therefore say how many cichlid species have disappeared forever.

The IUCN assumes that population numbers of H. vonlinnei had already declined during the 1970s. This also explains why there are no records of the species’ occurrence after 1980, when some specimens of H. vonlinnei were caught by trawl fishing in Tanzania.

Further reasons for the extinction of the furu in Lake Victoria

I. Overfishing

The IUCN considers predation by the invasive Nile perch to be the primary cause of the extinction of H. vonlinnei. Of course, H. vonlinnei was also fished, but unlike the Nile perch, the species was not a fishing target—it was rather bycatch. There are indeed biologists who believe that the Nile perch was only partially responsible for the disappearance of the furu. Rather, overfishing was an important cause. Goldschmidt also writes that furu numbers had already declined due to fishing before the Nile perch appeared—at least at locations in the lake where fishing took place. However, once the Nile perch arrived, it could be demonstrated that furu also decreased at parts of the lake that were sparsely populated and where hardly anyone fished.

II. Eutrophication

Due to deforestation and possibly acid rain, nitrates and phosphates from agriculture were washed into Lake Victoria, making the lake more nutrient-rich for algae. The result is seemingly endless fields of blue-green algae covering the water surface. This in turn causes the lake to be devoid of oxygen in those areas.

Another problem is the common water hyacinth (Pontederia crassipes), which as an invasive species covers vast areas of Lake Victoria. By overgrowing the water body, the floating plant causes the extinction of native fish and aquatic plants. In 1995, 90% of the Ugandan shoreline was overgrown with water hyacinth.

III. Hybridization

Furthermore, H. vonlinnei could potentially have been endangered by hybridization. The reason: since the 1920s, the lake has become increasingly turbid as a result of erosion and deforestation. Also, due to the reduced number of algae-eating fish in Lake Victoria since the Nile perch was introduced, the lake has become heavily eutrophic. The eutrophication and erosion in turn led to increased sedimentation, which ultimately reduced water clarity and impaired visual mate recognition. Female fish often choose their partners based on coloration, but when the water is turbid, mate choice differs from that in clear water.

Normally, different species do not mate successfully with each other, but among the furu this could work. The genetic relatedness between species is so close that fertile offspring can be produced. This is also how new species can emerge and old species can disappear.

IV. Water pollution

The increasing human settlement along the shores of Lake Victoria since 1960 also brings environmental problems such as water pollution. Due to intensive human settlement along its shores, the lake today faces significant environmental problems, including pollution and oxygen depletion. These crises led the Global Nature Fund to declare Lake Victoria the “Threatened Lake of the Year” in 2005.

How could so many cichlid species evolve in Lake Victoria?

In addition to the hippopotamus, countless fish species live in Lake Victoria—and most of them are cichlids of the genus Haplochromis. Since the last desiccation of the lake 12,000 years ago, not much time has passed in evolutionary terms, yet approximately 500 new species emerged in this brief period. The cichlids from Lake Victoria, Darwin’s Galápagos finches, as well as the fruit flies and the Hawaiian honeycreepers (such as the Ula-ai-hawane or the black mamo) of Hawaii are all textbook examples of the phenomenon of adaptive radiation.

Similar to the Galápagos finches and the Hawaiian honeycreepers, where beak shape adapted to specialized feeding habits, the same was true for the furu: their mouth shape and teeth took on many forms to adapt to a variety of ecological niches and different food sources. The cichlids changed morphologically and assumed specific roles. For example, there were piscivores, algae feeders, insect feeders, snail feeders, leaf eaters, scale eaters, and mud sifters.

The study Cycles of fusion and fission enabled rapid parallel adaptive radiations in African cichlids (2023), published in the journal Science, examines how the diversity among the furu came about. For this, the researchers analyzed 460 cichlid genomes. The result: the radiation could occur so rapidly due to a repeating process of hybridization and specialization. The species diversity in the lake is therefore not attributable to the immigration of fish from other bodies of water, but solely to the recombination of the genetic material of three ancestral species.

Through mixing and splitting of cichlid species, further species could emerge. The small piscivores, for example, originated from crosses between large predatory fish and small algae feeders. The new species are closely related to each other, yet differ in the way of life they have specialized in and the ecological niche they occupy.

H. vonlinnei—a piscivore

Dutch ichthyologists van Oijen and Frans Witte describe in Taxonomy, ecology and fishery of Lake Victoria haplochromine trophic groups (1990) 15 trophic groups among the cichlids of Lake Victoria. They classify the cichlids based on their diet and their food-processing technique. The largest of these groups are the piscivores, which include H. vonlinnei. Van Oijen discovered remains of smaller Haplochromis cichlids in the stomachs and/or intestines of the specimens used for the original description. For two of the five specimens, the length of the prey could be estimated at three to 3.7 centimeters.

The piscivores of Lake Victoria include at least 130 species, which also encompasses those that feed on parts of other fish or fish embryos, such as scale eaters and paedophages. The piscivores that consume whole fish (typically other Haplochromis cichlids) can be divided into two groups that exhibit different hunting behaviors: the first group attacks from ambush or plays dead and lunges forward when prey passes by. The second group, which usually consists of streamlined and fast fish, pursues their prey. It is not certain which group H. vonlinnei belonged to, but based on its body shape, it is assumed that it belonged to the second group.

Incidentally, the piscivores were the first Haplochromis cichlids to disappear after the arrival of the Nile perch in Lake Victoria, even though they occurred both in shallow shoreline regions at less than one meter depth and in open waters up to 50 meters deep.

What remains of Lake Victoria

The introduction of non-native species into an ecosystem can have drastic consequences for the food chain, as the example of the Nile perch clearly demonstrates. For the majority of furu species, the selection pressure that came with the presence of the Nile perch was too great, and they went extinct. But there were also some furu that survived, that were able to find an evolutionary response to the voracious predator quickly enough. It has been documented that some species changed their shape, becoming slimmer and faster to better escape the Nile perch.

The differentiated fish community that had developed over at least 14,000 years of coevolution disappeared from Lake Victoria within just a few years. An impoverishment of the ecosystem is the consequence: hardly any more furu, lungfish, elephantfish, or catfish. The Nile perch now occupies the position of the piscivorous furu and the furu-eating catfish in Lake Victoria. This means the Nile perch, as the sole predatory fish, has replaced more than a hundred predatory fish species.

It is clear that the situation with the Nile perch cannot continue forever, as its most important food source, the furu, has largely disappeared. In the mid-1980s, more than 80% of the fish biomass in the Kenyan part of Lake Victoria consisted of Nile perch—an actually untenable role for a predator at the top of the food chain. Yet the Nile perch persisted. The reason: the explosive increase of Caridina nilotica, the only shrimp species living in Lake Victoria. With the disappearance of the furu, this shrimp has become the most important food source for the Nile perch. The shrimp were able to reproduce in such massive numbers because they replaced the detritivorous furu, at least 13 species. It remains to be seen what the future holds for Lake Victoria and its inhabitants.