PAUL SACKLEY maintains a constant vigil over 12 precious freshwater fish tanks at the New England Aquarium. His wards, silver, black, and blue-green cichlids (pronounced sicklids), swim lazily through the dead branches and decorative debris, unaware that they may be the few survivors of a voracious predator in Lake Victoria, Africa - the second largest freshwater lake in the world.
``Victoria is becoming an aquatic desert,'' says Humphrey Greenwood, a retired ichthyologist formerly with London's Natural History Museum. He spent much of his professional career studying the biology of the lake.
The culprit is the Nile perch. Since its introduction in the 1960s, this predator has been eating the lake clean - wiping out the major constituents of the lake's native fauna that range in length from a few inches to a foot.
``We are watching a giant, true-to-life mass extinction experiment,'' says Les Kaufman, an ichthyologist with the New England Aquarium in Boston.
``Lake Victoria is a wonderful example of how lake management should not be done,'' says Mesho Gophen, senior scientist at the Yigal Allon Kinneret Limnological Laboratory in Israel.
The 27,000-square-mile lake, bordered by Kenya, Tanzania, and Uganda, was once home for 250 to 300 species of cichlids - 99 percent of which are found no where else in the world.
``It is tragic,'' says Peter Ochumba, one of four African scientists involved with project. ``Many of these fish have never been described and now they are facing extinction.''
The Nile perch, which averages four feet in length and weighs up to 400 pounds, was introduced by British colonial officials primarily as a sport fish. The mature fish could not be caught by local fishermen - their fine nets, adapted to cichlid fishing, were too weak to hold the larger fish.
In the late 1970s, the Nile perch population suddenly boomed, Dr. Kaufman says. It appeared in all parts of the lake, leaving in its wake a trail of destruction.
Lake Victoria is representative of what is happening all over the world.
``Extinctions are going on everywhere, everyday,'' Mr. Sackley says. ``And it's important to know the dynamics of what happens. We are wrestling with what can be saved and what will be lost. It is a powerful lesson, but a good one.''
The lake's troubles have drawn a team of scientists from bordering countries, as well as from Canada, the Netherlands, Israel, and the United States. They have joined forces to investigate and decide what, if anything, can be done.
In a last-ditch effort to save the lake's fauna, Kaufman and scientists in the Netherlands and Britain initiated a captive breeding program. Representatives from as many species as possible are flown in plastic bags and containers some 5,000 miles to Boston from Kisumu, Kenya, one of the African research bases. From there they are distributed to aquariums and zoos worldwide.
Sackley, a graduate student at the University of Massachusetts, will be leaving Boston at the end of July to help African scientists establish a captive breeding headquarters in the laboratory at Kisumu.
The breeding program, initiated in 1987, already has one success story. One plankton-eating cichlid believed to be extinct in the lake is alive and well at the aquarium, as well as at the University of Leien in the Netherlands and the Oklahoma City Zoo.
Lake Victoria is the source of livelihood for villagers living up to 100 miles inland, according to David Wiley, director of the African Studies Center at Michigan State University.
Prior to the Nile perch, the traditional fishing industry and lifestyle was based on cichlid fishing in the relatively shallow bays and inlets of the lake. The small fish could be easily caught by villagers' nets and dried on the beaches in the hot African sun. This was the main source of protein for more than 8 million people, Dr. Wiley says.
The perch, a much larger and oil-rich fish, cannot be dried in the sun. It must be smoked, refrigerated, or deep-fried before it is edible. Few villagers were equipped with the resources to catch or process the new fish.
With the help of commercial fishing companies, a new fishing industry arose in parts of the lake, providing jobs, a new fleet, and improved roads for transporting the perch.
If the story of the Nile perch is examined in the short term, it is a success, Dr. Gophen says. ``But in the long term it is a disaster.''
Wiley is leading a team of African and American social scientists examining the effects of the perch on the local people. Although the results are not yet conclusive, Wiley believes there may actually be a reduction in jobs for the villagers because they cannot afford the large equipment necessary to fish the perch and the commercial fishing companies are using modern equipment, which does not require as much labor.
``Also the taste that the people want is gone,'' says Dr. Ochumba. ``The new fish is highly priced so they cannot afford it, and they are losing something they prefer.''
There is one more wrinkle. With much of the native prey gone, says William Cooper, aquatic ecologist at Michigan State University, the perch has begun feeding on its own young. Combining the high rate of commercial fishing with the cannibalism among the perch, the fish may be at the early stages of a population collapse. This may mean a collapse of the perch fishing industry as well.
``There has already been a decline in the landing of the Nile perch,'' Gophen says.
``We may be able to protect some of the native fishes in their natural habitat in certain parts of the lake,'' Dr. Greenwood says. ``But this must be done quickly while there are fishes to save.''
One African scientist believes Lake Victoria may achieve a new biological equilibrium with the Nile perch at the top of the food chain.
At best, scientists hope that what happens here will improve lake management policies in the future. ``Victoria stands as the best example of what not to do,'' Greenwood says.