Captive breeding promotes aggression

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Fish bred in captivity can become more aggressive than their wild counterparts, limiting their suitability for reintroduction into the wild, says new research.

Captive-bred Butterfly splitfin livebearers, Ameca splendens, become much more aggressive when bred in captivity, with aggression levels believed to be linked to environment and stocking density.

Jenny Kelley and Anne Magurran of the University of St. Andrews in Scotland worked with Constantino Macias Garcia of the Instituto de Ecologia in Mexico to examine the behaviour of wild Ameca splendens to those bred in a captive-breeding programme at the London Zoo Aquarium.

The scientists have just published their findings in the latest issue of the journal Biological Conservation.

The results showed that wild fish were preoccupied with searching for food, while captive fish spent much of their time in aggressive interactions with other fish.

The way the aquarium was furnished and the number of fish in the tank also played a part in determining the level of aggression in the captive goodeids.

Captive male goodeids were most aggressive when kept in "structured" or furnished aquaria, rather than in "unstructured" or bare tanks, but only when they were stocked at a high density.

A furnished aquarium also meant that the fish spent less time foraging for food, compared to bare tanks in which they forage for much of their time.

The authors said: "The findings of this study suggest that captive breeding can result in behavioural divergence in wild and captive-bred endangered fish.

"This could cause problems if captive-bred individuals are released into the wild.

"In the case of the Butterfly splitfin, aggressive males may have problems reproducing if attacks are directed towards females, or they may be at greater risk of predation through reduced vigilance and increased conspicuousness."

For more information see the paper: Kelley, JL, AE Magurran and CM Garca - (2006) Captive breeding promotes aggression in an endangered Mexican fish. Biological Conservation 133: 169-177.