A lake in chaos

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Lake Victoria is a hotbed of cichlid evolution with several hundred species known and most undescribed. Yet, with introduced predators and water pollution, these fish are under great threat, says Nicolette Craig.

It seems a mystery to me that Lake Malawi and Tanganyika cichlids receive such attention while cichlids from Lake Victoria are only really appreciated by serious cichlid enthusiasts. It is doubly sad considering the conservation disaster that Lake Victoria has become.

I recently talked to Professor George Turner, honorary president of the British Cichlid Association and head of biological sciences at Bangor University, who said: “Aquarists are much less interested in Victorians and I am not sure why.

“It could be the difficulty in telling species and populations apart, or maybe that the females and juveniles of most species look the same and are very drab. Males also lose colour quite easily and you often only have one or two dominant-coloured fish in a tank of drab things. In addition there is a lack of a good exporter on the lake and, as a result, not many good quality stocks.

Lake Victoria is the world’s largest tropical lake. It covers an area the size of Switzerland and straddles Tanzania, Uganda and Kenya. At its deepest point it is around 80m/260’ deep, yet as recently as 14,000 years ago it was thought to have been a dry plain.

Going back just 60 years this lake was amazingly species rich, with over 500 endemic haplochromine cichlid species, 17 cyprinid species, 10 catfish species and 18 other species divided over five families.

The cichlids showed an astonishing diversity. Virtually all habitats and food types were exploited, including species feeding on plankton, algae, snails and bivalves, insects, crustacea, other fish, and even cichlid eggs and larvae stolen from the mouths of brooding females. It appears that all of these cichlids may have evolved in just over 14,000 years.

Today, the fisherman that can be seen around the lake pull catches dominated by two species that were never found here in the 1950s — the Nile perch (Lates niloticus) and the Nile tilapia (Oreochromis niloticus). The cichlids have dwindled by nearly 50% and it seems hard to imagine that the lake was ever a hotbed of diversity.

The reasons behind one of the largest vertebrate extinctions of our time are manifold. Firstly, the perch and the tilapia that are now ubiquitous in the lake were introduced as food sources to increase the fishery yields of the lake. The Nile perch is large and predatory and eats many of the other fish in the lake, whilst the Nile tilapia, a plankton eater, acts in competition with some of the other species of cichlids. Ironically, it seems that overfishing of the haplochromines in the 1970s may have given the Nile perch the foothold it needed to take over.

Next, the countries surrounding the lake have experienced a huge population and developmental boom. Together with deforestation, this has led to an accompanying increase in pollution produced. As a result, oxygen levels in the lake have dropped to such an alarming extent that the bottom of the lake is uninhabitable.

Higher up the trophic levels the pollution has led to a huge increase in the amount of algae which cuts off oxygen supplies, drastically reducing visibility and, when it dies, producing even more pollution.
Finally, and adding to the tragedy, the increase in pollution provided food material for the invasive water hyacinth weed. This has spread over the lake and interfered even further with light penetration, dissolved oxygen, fish breeding sites, landing beaches and ecology.

In Lake Malawi and Lake Tanganyika males and females of different cichlid species can see each other clearly to differentiate between species. In Lake Victoria however, the visibility is down to below a metre. These cichlids rely strongly on colour to differentiate between species that are morphologically almost identical. In an environment where the female can’t see to choose a male of the right species let alone the best quality this ultimately leads to a great deal of hybridisation.

 

What can be done to help?
So amid these tales of doom and gloom, can anything be done to help these fish? Brian Zimmerman, the assistant curator at ZSL aquarium, was involved in a European ex-situ conservation programme for cichlids which focussed on Lake Victoria cichlids. Last year the group was abandoned after ten years.

He told PFK: “We realised that as a group we were really serving no purpose. The ultimate game plan has to be maintaining genetic diversity. However, with Lake Victoria cichlids this is very tricky. For a start it is nearly always only a few individuals that breed and that leads to genetic bottlenecks. In addition, haplochromines in the wild cover a huge range of niches and the cichlids show a wide range of morphological features. In captivity we just can’t replicate this, and after a few generations we find their morphology starts to change back to a generalist type.”

In an echo of this problem the British Cichlid Association had to close down their Private Breeders programme and the remaining conservation programme in the US is now also considering where it goes next.

Professor Turner doesn’t agree though. He feels that there is still a lot of potential for Lake Victoria to become a source of aquarium fish. He said:“There is probably untapped potential for aquarium fish in Victoria. We had a lot of interest in excess Lake Victoria we bred in the past, including Pundamilia nyererei. Pundamilia igneopinnis, Paralabidochromis sp. ‘Rock Kribensis’ and Paralabidochromis chilotes are all attractive fish, but there is no commercial supply of these.

“When I visited the Ugandan part of the lake, there was something there that looked like a pink Labidochromis caeruleus. It was small, brilliantly coloured (both sexes, I think), behaved like it ought to be peaceful and could be a ‘flagship’ to get these cichlids some wider recognition. As far as I know, it is undescribed, has never been photographed alive and is yet to be exported.”

A team led by Dr Frans Witte based in the Netherlands have now started to see signs of recovery in the lake, with more cichlids appearing in catches. They have also discovered that in just 20 years some species of cichlids have started to evolve; gills, jaws, eyes and head shape are all changing in morphology to adapt to their new environment.

Whatever this means, there may still be hope for Lake Victoria.

Expert Q&A

 

Ichthyologist Frans Witte is an associate professor in integrative zoology and is renowned as a specialist in the morphology, taxonomy, ecology and biodiversity of haplochromine cichlids from Lake Victoria, East Africa.

What attracted you to Victorian cichlids?
In 1974 I started a project for my masters’ thesis on the morphology of haplochromine cichlids. My supervisor visited Tanzania to collect live fish and heard of a proposed fishmeal factory near Mwanza that would convert 30 tons of cichlids per day into fodder. He realised that there was little known about the ecology of the haplochromines and that there were still many unknown species. He was afraid that species might be lost by over-fishing, so he proposed to start a research project in Tanzania.

There has been some evidence of recovery in Lake Victoria. Could you tell us about this?
Since the decline of Nile perch over the last decade, about 25% of the species that were lost from the sub-littoral habitats have recovered. They mainly belong to the detritus and zooplankton-feeding groups. We are currently studying these recovering species and it appears that they changed, both ecologically and morphologically. They have all changed their diet and, even more excitingly, their morphology has also changed: for example. a different head shape, larger gills, changes in the eyes, jaw muscles and intestine lengths. These seem to be adaptive responses to the changed environment.

Do you think that there could be hope for the future of Lake Victoria?
It certainly seems less hopeless than we thought at the beginning of the 1990s, when Nile perch made up 99% of the catches in the sub-littoral. However, many have still not returned; in particular the highly specialised piscivores, paedophages, scale scrapers, parasite eaters, for example. We think that some more species might return if the eutrophication could be reduced and the water becomes clearer and oxygen rich again, so giving a chance to species that might have survived in some rare refugia. However, a lot of damage has already been done and many of the fish that we currently catch seem hybrids of former species.

Lake Victoria: The facts

  • 200: The number of cichlids thought to have now become extinct.
  • 80: The maximum depth of Lake Victoria measured in metres.
  • 6800: The area in square kilometres covered by Lake Victoria.
  • 3440: The distance in kilometres around the lake's shoreline.
  • 30 million: The number of people who live around the Lake basin.
  • 1m: The visibility in metres in the 1950s.
  • 5m: The visibility in metres in the 1930s.
  • 90%: The percentage of the Ugandan coast covered by Water hyacinth.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.