Air Date: Week of October 25, 2002

Living on Earth’s Maggie Villiger reports on why some fish fathers engage in filial cannibalism.

Transcript

CURWOOD: Just ahead, the joy of exploring the night sky. First this page from the Animal Notebook from Maggie Villiger.

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VILLIGER: Some fish fathers practice a brutal form of tough love. They eat some of their offspring while continuing to care for the rest of the brood. Scientists thought that eating some eggs would provide the fish dad with extra energy to care for the remaining eggs.

Researchers recently put this theory to the test. They fed supplemental meals to one group of male Beaugregory Damsel fish guarding eggs. Another group of fish had to forage for themselves.

After the sixth day, the fed fish were fatter, but just as prone to cannibalism. So the researchers set up another experiment with some fathers in a heavily aerated tank with lots of water flow, and a second group in an unaerated tank with little water circulation. This made a difference. The aerated fathers were much less likely to eat their young.

Researchers think the important factor influencing fish cannibalism is how much oxygen is available. With more oxygen in the water, embryos develop faster and healthier. It looks like cannibal dads randomly eat eggs throughout the clutch to reduce overall egg density. That way, remaining eggs have more exposure to oxygen and a better chance of survival. That's this week's Animal Note. I'm Maggie Villiger.

CURWOOD: And you're listening to Living on Earth.

[MUSIC: Billy Strayhorn, “Take the A Train” THE PEACEFUL SIDE OF BILLY STRAYHORN (Capitol, 1996)]