It's been my experience, not sure about others....that fingerlings are more sensitive to most out of whack parameters. I don't find this specific to species. Not sure if it's due to size, making them more sensitive, or if it's a maturity issue, or what have you. But when I take semi adults/adults and expose them to the same stresses as fingerlings or even juevies the younger always shows stress and ailments long before the adults. Especially true with amonia, and DO issues for instance when a pump burns out, or I over stock, transport, etc. I do believe though, that changing a considerable amount of the water will help. There's a quote I saw somewhere of "stop polution through dilloution" Or something like that. And I have found this to be very helpfull. Does anyone else have experience in this?