The genetic challenges of captive breeding

Australia has a unique freshwater fish fauna, with over 75% of species found nowhere else in the world. Unfortunately, more than 10% of these species are under serious threat of extinction, mostly from loss and degradation of their freshwater habitat. One option which is now being considered to help conserve native fish species is breeding them in captivity and then releasing captive-bred fish to boost population sizes in the wild. This raises many challenging questions.

First, where should we collect the fish for the captive-bred population? Can we assume that all fish of the same species are the same, or is there important genetic variation between populations in different rivers?

Secondly, how should we go about a successful breeding program? How many fish do we need to collect to found the breeding population? Should we put all the breeding animals together and let nature take its course, or establish male and female pairs and let them breed separately?

Thirdly, how should we release the captive-bred fish? Will captive-bred animals survive and reproduce in the wild? Should they be released only into rivers from which that species has disappeared?

These are all questions involving evolution and to answer them requires an understanding of evolutionary theory.