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Male Fish Cannibalism Puzzles Researchers

Posted on: Friday, 24 August 2007, 06:10 CDT

MILWAUKEE -- On the other side of the world, in the waters of a remote ancient lake on the island of Sulawesi, Indonesia, Jeff McKinnon made a strange observation.

McKinnon, a University of Wisconsin-Whitewater biologist, saw that males of the Telmatherina sarasinorum species of fish were using their mouths to pick at the surface of the area where the females had just laid eggs.

He and his team later found eggs in the bellies of male fish they caught, and they inferred that in picking at the surface the fish were eating eggs.

And these weren't just any eggs: They were eggs the male had fertilized only moments before _ potentially, his own future offspring.

This filial cannibalistic behavior, where male fish eat eggs that could be their own kin, is fairly common in nature among fish that spend energy caring for their offspring after they hatch.

The T. sarasinorum species, though, doesn't take care of its offspring, and this is the first time that cannibalistic behavior has been seen in a fish with no parental care.

The unique fish exists in only one lake on the island of Sulawesi, and its habitat is threatened by increasing land development and dumping. McKinnon and his collaborators began a local conservation and education effort with government officials and mining representatives to preserve the habitat of the creatures living in Lake Matano.

Sulawesi boasts diverse flora and fauna. As a transition point between Asian and Australian species, the "K"-shaped island in the center of Indonesia has been isolated from the other continents for some time, allowing its native species to evolve independently.

Many species on Sulawesi are endemic to the island, found only in that one corner of the world. Aquatic species, such as fish and snails, are especially unusual.

The ancient Malili lake system on Sulawesi _ which includes the Matano, Towuti, Mahalona and Wawontoa lakes _ is a few million years old. Although the lakes are separated by only tens of kilometers, they have completely different sets of species.

"Everything is endemic over very fine scales, miles," McKinnon said. "With such limited ranges, these species are very vulnerable."

At a higher altitude than the others, Lake Matano is separated from the other Malili lakes by geographic barriers.

A waterfall leading from Matano down to Mahalona and Towuti prevents fish from those lakes from swimming into Matano, keeping the fish biodiversity unique and separate.

Lake Matano is the deepest lake in Indonesia and one of the deepest lakes in the world. It's also the only place that the small, colorful T. sarasinorum fish call home.

A male fish will spend a great deal of energy courting the female, encouraging her to lay eggs so that he can pass his genes on to the next generation.

But sometimes other male fish, appropriately named "sneakers," will swim in next to a couple and attempt to fertilize the eggs before the courting male.

In a study published in February in the journal American Naturalist, McKinnon and his colleagues found that males would sometimes eat the eggs a female had just laid and that the male had just fertilized, if other males were present during spawning and could have fertilized the eggs first.

The more sneaker males present, the more likely it was that the courting male would eat the eggs, since they were less sure of their paternity.

They were three times as likely to eat the eggs if one sneaker male was present during spawning, and six times as likely to eat the eggs if two or more sneaker males were present.

Females don't eat their own eggs, presumably since they can be sure of maternity, but they will eat eggs of other fish species.

Egg-eating is common among fish. Most species regularly feed on the eggs of others, and McKinnon and his team have speculated that this may predispose the fish to cannibalistic behavior. "When they cannibalize, they are doing something they do normally, but to their own species," he said.

It seems counterintuitive that fish would eat their own future offspring, especially when the fish spend no energy in caring for their offspring.

"If you're going to eat eggs, they shouldn't be your relatives," McKinnon said.

McKinnon has a long history with the ancient Sulawesi lakes.

His first visit to the lakes was in the summer of 1981, as an 18-year-old biology student at the University of British Columbia. McKinnon spent a few weeks vacationing with relatives at the lakes, swimming and collecting insects.

"I always had in mind I would like to go back to that part of the world," he said. Twenty years later, he made it.

His first science-oriented research trip to Lake Matano was in 2000, and he's been going back every couple of years since.

But each time he returned to Sulawesi, he noticed disturbing developments that were threatening the environment around Lake Matano and the habitat of the T. sarasinorum and other creatures in the lake.

One of the biggest dangers is the introduction of non-native fish species, which expose native species to disease and force them to compete for the available food.

Locals make deliberate efforts to stock the lake with carp and tilapia as a food source, and often unwanted aquarium fish are dumped into the lake.

Water pollution is a concern for many with ties to the lake _ a hydroelectric power plant and a large mine sit on its nickel-rich southern shore.

Deforestation and erosion, too, are threatening fish habitat in Lake Matano.

Trees are cleared to make way for roads leading to the nickel mine, and erosion becomes a problem. Sediment is washed into the lake after heavy rainfalls, clouding the water near the shore and preventing researchers from observing the fish.

"Roads always lead to environmental degradation," McKinnon said.

Threats to the ecology of Sulawesi and its unique species have prompted conservation and education efforts by governmental officials and scientific researchers.

"Lake Matano is really a magnificent piece of Earth," wrote Peter Hehanussa, senior member of the Indonesian science agency LIPI, in an e-mail.

"Not only the species ... but water resources on this island, and especially around Lake Matano, are very dependent on the health of the ecosystem around it," he said.

McKinnon worked with Hehanussa and LIPI to design a poster campaign to educate locals against introducing non-native fish species into the lake. Inco, the company that owns the nickel mine on Lake Matano, printed and produced the posters, which were distributed around the community.

McKinnon and his team gave talks to the community, school groups and mining staff on the need to think about conservation and preservation of this special environment. He also has spoken at conferences and symposiums in Indonesia and around the world on the ancient Malili lakes.

Suzanne Gray, a postdoctoral student at Queen's University in Ontario, who worked with McKinnon studying the T. sarasinorum for her doctoral thesis, was also involved in conservation efforts during her trips to Lake Matano.

She gave a series of seminars to local high school students, encouraging them to think about the lake and its importance to their daily lives. The students designed posters that would bring awareness to how special the lake is to the community.

Gray felt that her efforts were successful: "I felt like the people I was able to talk with and interact with had a better appreciation for the lake."

McKinnon feels a sense of obligation when it comes to conservation: "We need to take care of the house."

Source: The Milwaukee Journal Sentinel

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