A sad tale of how economics and misuse of natural resources killed hundreds of species.
Paul V. Loiselle
Q. I've heard many different rumors about Lake Victoria in Africa and would like the facts from someone in the know. I understand the Nile perch has gotten into the lake and wreaked havoc on its native fishes. I am wondering what the extent of damage to the cichlids of the lake has been, and what, if anything, is being done about this?
I am currently keeping breeding colonies of a number of Lake Victoria cichlids. These are beautiful fish, but there seems to be limited information in print about them, and they are rarely found in retail pet stores. Why is it that so few of these fish have formal Latin names?
A. Your letter covers a number of aspects regarding Lake Victoria cichlids, and I will try to answer them. To address the last issues you raised first, the current unsatisfactory nomenclatorial status of many Lake Victoria Haplochromis reflects the fact that there are more species than anyone expected. Extensive collecting in the Kenyan and Tanzanian waters of Lake Victoria has turned up large numbers of undescribed species. These fish are being slowly worked on, but in the meantime, researchers and hobbyists alike have to call them something — hence the large number of nicknames for these fish.
Given that they have been available to hobbyists for a rather short time, it is not surprising that the body of information in print on the husbandry of these cichlid fish is relatively small. The sections of my book, A Fishkeeper's Guide to African Cichlids (distributed in the United States by Tetra Press), dealing with basic husbandry contain information a Lake Victoria cichlid keeper would find useful. A more detailed treatment of the natural history and husbandry of Victorian haplochromines can be found in the second edition of The Cichlid Aquarium, from Tetra Press.
The quarterly magazine Cichlid News frequently features articles dealing with the care and breeding of Lake Victoria Haplochromis. You should find it a good source of information on newly available species, as is Buntbarsche Bulletin, the journal of the American Cichlid Association.
The Nile perch (Lates niloticus) was initially introduced into Lake Victoria in 1954. This introduction, together with that of four exotic tilapia species, was made in response to the collapse of the original Lake Victoria fishery due to overfishing of two native tilapias (Oreochromis esculentus and O. variabilis). The idea was that the large, predatory Nile perch would feed on the lake's Haplochromis species, and in turn become a food fish for the locals.
For reasons that remain a mystery, the numbers of Nile perch remained relatively low until the mid-1980s, when it underwent a population explosion. Within a space of a few years, the Nile perch simply ate its way through the cichlid fish of Lake Victoria. Because the Victorian cichlids had not been completely catalogued at the time, we can never know precisely how many cichlid fish species perished in what may be the largest vertebrate extinction in tens of millions of years. A widely accepted estimate is that 300 of some possible 500 haplochromines native to the lake have become extinct since 1980.
As appalling as this figure may be, closer examination of the pattern of these extinctions reveals an even grimmer reality. Lake Victorian cichlids, like those of Lake Malawi and Lake Tanganyika, are an outstanding example of the phenomenon of adaptive radiation. Simply put, if there was a way for a fish to make a living in Lake Victoria, a haplochromine cichlid fish evolved to take advantage of it. These Haplochromis managed to invent a lifestyle quite without parallel elsewhere! Fish ecologists recognize 10 to 14 distinct trophic guilds — assemblages of species with a common feeding pattern. However, not all were equally impacted by Lates.
Many piscivores, embryo eaters, parasite cleaners, fin and scale eaters, bottom-dwelling insectivores and phytoplankton feeders either no longer exist or else are represented by one or two surviving species whose future is far from certain. Physically similar insectivores, detritus feeders and algal grazers, on the other hand, are still well represented in the lake, largely because they occur in habitats that afford them a degree of protection from the depredations of the Nile perch. Thus, Lake Victoria's cichlids have become much less physically and ecologically diverse, with many fewer species.
The duration of the Nile perch's impact on the Lake Victoria ecosystem is open to question. I suspect that if one considers direct impact only, Lates has done its worst. Those haplochromines still in existence have, by virtue of their persistence, demonstrated that they have the ability to coexist with this formidable predator. However, the elimination of so many of Lake Victoria's cichlid fish has had far-reaching effects upon the lake's ecology, and it is by no means certain that these have run their full course.
Since at least the 1920s, Lake Victoria has been undergoing a progressive shift from a nutrient-poor to a nutrient-rich state. This process has been driven by the progressive deforestation of its watershed, which accelerates the movement of such plant nutrients as nitrates and phosphates from the soil into the lake. Increased nutrient levels have resulted in increased planktonic algae.
Prior to the introduction of the Nile perch, these algal blooms supported a diverse community of planktonic crustaceans, as well as a substantial assemblage of phytoplankton-feeding Haplochromis species. These small, open-water cichlid fish were among the first casualties of the Nile perch's voracious appetite. With their removal from the food web, vast quantities of phytoplankton remain unconsumed, die and fall to the bottom. Here their decomposition has had the effect of turning the formerly well-oxygenated deep waters of Lake Victoria into an oxygen-deficient environment — killing or forcing into shallower water the distinctive Haplochromis species of this zone. Sixty feet now marks the lower distributional limit for oxygen-consuming organisms in Lake Victoria.
The fact that most of the lake's volume can no longer support oxygen-dependent life is bad enough. Even more alarming is that no one seems to be able to predict at what point — if any — the oxygen and non-oxygen zones will reach a stable equilibrium. One possible outcome is that below a depth of a few inches, Lake Victoria will become entirely oxygen deficient, and even the Nile perch will perish along with the surviving remnants of the lake's cichlid fish.
Note that eliminating Lates from the picture at this point would not reverse this trend. The phytoplankton feeding Haplohromis are gone forever. Indeed, the extermination of so many cichlid fish species precludes restoring Lake Victoria even if the means existed to eradicate the Nile perch from the world's second largest freshwater lake.
It is, in any event, also doubtful that the political will exists to restore the lake to its former condition. From the standpoint of the Kenyan, Ugandan and Tanzanian governments, the Nile perch is anything but a disaster. Lates supports an extremely lucrative export fishery that earns them significant sums of hard currency. Ordinary Africans, for whom sun-dried tilapia was a dietary staple and is now a luxury food since the Lates invasion, doubtless have a rather different perspective on the matter, but their views have little impact upon policy decisions in the current political climate.
In response to the plight of Lake Victoria cichlid fish, the Association of Zoos and Aquariums has established a Species Survival Program (SSP) for these fish. A comparable program has been established by European zoos and public aquariums. The short-term objective is to establish viable captive populations of species known to be seriously threatened or even extinct in nature. The long-term objective is to return as many of these fish as possible to a more natural environment in Africa.
The organization keeps abreast of developments in Lake Victoria and does not exclude the possibility of reintroducing some of the fish it manages to the lake proper should Lates numbers drop significantly. However, restocking efforts at this point are likely to prove nothing more than an expensive supplementary feeding program for Nile perch.
However, a number of large reservoirs in Kenya's lake district have been surveyed that offer the promise of supporting relatively simple assemblages of Victorian Haplochromis. Current efforts are focused on stocking three of these reservoirs with species presently under program management. If you are interested in following these developments more closely, I suggest you join the Aquatic Conservation Network, whose bulletin, Aquatic Survival, serves as the official channel for information on the efforts of the SSP to save and restore the lake's cichlid fish.