It is my understanding that a high protein feed damages the liver of catfish. So, all fish do not metabolize in the same way.
Excess protein fed to any fish will damage the kidneys to some degree. Yes excess protein is treated as waste. In adult fish its all about maintaining muscle and tissue. How can this vary from a carnivorous bass to an omnivorous catfish? The same size fish has the same mass of muscle and tissue to maintain.
