Are captive-bred fish released into the wild?

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Do any captive-bred fish that are endangered in their natural habitat ever make it back to the wild? Rupert Collins has the answer.

So far, the conservation status of only 10% of more than 31,000 fishes has been assessed, but 1,273 species have been classified as vulnerable or endangered. Currently 13 species are considered extinct in the wild but still maintained in captivity.

Captive breeding programmes, such as those of the Butterfly splitfin (Ameca splendens)  undertaken at London Zoo have kept the lineages alive.

Releasing into the wild depends on whether the habitat is fit enough for them and whether sufficient funds actually exist for the necessary long-term monitoring of the species’ genetic diversity and environment.

When fishes are prized for sport or food, however, wild populations are frequently augmented with hatchery fish, yet studies have demonstrated that captive-bred stocks of Rainbow trout are poorly adapted to the wild and less likely to survive and reproduce.

Higher population densities in captivity have also been shown to make fish more aggressive.

Captive breeding for conservation should be a last resort — or a temporary safeguard.

There are huge consequences though for indiscriminately releasing any aquarium fish into the wild and many can become pests, like the Common plec (Pterygoplichthys pardalis), now invasive in more than a dozen countries. New deadly diseases can also be spread, decimating native creatures and ecosystems. A fish should never be released into the wild after being in an aquarium.

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