In 1954, copper waste in the Finniss River killed numerous fish - VCE - SSCE Biology - Question 16 - 2009 - Paper 1

The increased population of the black-banded rainbow fish despite the copper waste suggests that these fish possessed a pre-existing ability to filter and eliminate copper from their bodies. This adaptation would have allowed them to survive in an environment that was detrimental to other fish species. Therefore, it can be concluded that the ability of their gills to remove copper was not a new mutation occurring in 1954 but rather an existing trait that enabled their survival.