The Plight of the Lake Victoria Cichlids
by Sean Furney, Oklahoma City
Reprinted with permission, from Sean's website www.theaquariumexchange.com
Aquarticles
Lake Victoria was discovered in 1858 by British explorer John Speke. It is one of the
largest lakes in the World, covering 26,560 sq. miles. As recently as 12,500 years ago the
Lake is believed to have been a grassy plain. This makes it the youngest of the three
African Rift Lakes. The Lake is believed to be the most rapidly developing lake in regards
to rapid growth of species numbers, with over 200 distinct species developing since it
came into existence. In that regard Lake Victoria may be developing species more rapidly
than in any other animal group in the entire World. With this in mind it is quite tragic
that the native population of cichlids is dwindling at a very rapid rate. There are
several theories that scientists have for the rapid depletion of the cichlids. I will
cover each briefly in the article.
The first of these is one that for a number of years was believed to be the sole
reason, or at least it was the most widely publicised one. This reason is the introduction
of two non-endemic species of fish. In the 1950's British colonists introduced the Nile
Perch (Lates niloticus) and the Nile Tilapia (Oreochromis niloticus).
The Nile Perch is quite a predatory species that is believed to be the main reason for the
decline. The Nile Tilapia, on the other hand, is a plankton eating fish which may not have
had a great affect on the native cichlid population, but may be competing for food with
some of the species. These fish were introduced to provide a food source for many
countries. They grow much larger than the cichlids that exist in the Lake. It is this
size, combined with the predatory behavior of the Nile Perch, that scientists believe is
too much for the native populations of cichlids. However in recent years, scientists have
come up with several new theories on what is causing the decline of the native cichlid
populations.
One of these new theories has to do with the vast amount of pollution that is flowing
into the Lake from the surrounding countries. The countries that surround the Lake have
undergone a substantial population boom in recent years, vastly increasing pollution. At
the present time oxygen levels at the bottom of the Lake are not great enough to support
life. Lake Victoria is on the verge of becoming a dead lake. Another part of this theory
is that visibility is so poor that the brightly colored cichlids in the Lake are having
trouble correctly identifying mates, and therefore not mating as often. This pollution is
a contributing factor to some of the other problems in the Lake.
The next problem is the increase of algae levels in the Lake, with pollution providing
the necessary nutrients for algae growth. The algae levels are five to ten times the
levels of the 1960's. This algae then dies off, creating more pollution and contaminating
the Lake further. Visibility levels are measured in the Lake by checking the depth at
which a white disc is visible under the water's surface. This test has shown decreasing
visibilities, from a depth of about five meters in the 1930's to a depth of one meter or
less in 1990. This is a serious danger to the Lake. As pollution levels go up algae growth
goes up. In turn the algae that dies off creates more pollution in an apparently never
ending cycle of lake destruction. This is even having a great impact on the people who
live around Lake Victoria. With these algae blooms comes an increase in the dangerous
blue-green algae, causing more disease in the human population. Along with this growth in
algae is the development of the Water Hyacinth plant. This plant was unseen until 1989,
but since then has exploded to choke out harbors and coves.
As you can see the situation is dire. So in your cichlid keeping experience please
don't forget the gorgeous cichlids from Lake Victoria and their desperate plight.
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