A. This is very difficult to answer and what I say probably won't entirely satisfy you. The problem is that optimum temperature ranges for any activity can vary from species to species and among different populations of the same species. This is because optimum temperatures for spawning, feeding, etc. are largely determined by the temperature to which the particular population has been acclimated. A population of rainbows living in a relatively warm stream or lake will have different optimal feeding temperatures than a population acclimated to a cold environment. In general, warmer temperatures increase metabolic activities up to a point; then it adversely affects growth, movement, feeding, etc.