If they can't live in it somethings deadly wrong!
We often need to prove that fishes are indicators....They are capable of sending us precise and accurate signals of the "ecological" quality of inland waters. And there is value in pursuing this. But as everything in nature - weird and wonderful noise abounds. And people need to use both common sense and a greater sense of natural history in interpretations. Just looking a the waters through fish eye's may really be enough to tell us if the conditions are natural.