Forgive me if I am totally off base, but it is my understanding that fish in general only "slow" their feeding in the winter when it is cooler because the lower temperatures take their digestive tracts out of the optimal temperature range for reactions to take place (the optimal pH / temperature balance).
This would effectively lead to a decreased rate in digestion (depending on the protein source / type).
Their digestive tracts are not processing food items optimally, so they don't eat as often because their digestive tract can only hold so much food, and process it only so quickly in sub-optimal conditions.
So what effect might this have on growth rate in the winter?
Well, for one we would need to take into account the type of protein / foodstuff being provided. What is the digestibility of the said food item?
Using common sense I would surmise that a fish (bluegill, bass, whatever, just arbitrary at this point) may not grow very quickly or very much at all if it is eating natural forage, and breaking down complex proteins.
It might be able to process the prey items just quickly enough with a lowered rate of digestion to maintain its current body weight, and maybe put on a little weight or grow a bit.
If that fish on the other hand were fed a high quality, highly digestible pellet based feed (Assuming that many of the same principles of livestock and companion animal nutrition are used in fish nutrition), then I would expect those fish to process those pelleted feeds at a higher rate than they would natural forage. I would expect to see a measurable amount of growth even during the winter on pellets. But then again, this is a gross generalization. Not everyone has the same intensity winters or water temperatures.
Sorry for bringing this topic back from the dead. It is a topic I am very interested in academically, although I'm more of a companion animal / ruminant nutrition kind of guy.
I could be totally off and have wasted your time. I don't know anything about fish really, I just assume from my studies that there is significant overlap between species and the principles of digestion. There are a lot of confounding factors like Genetics and probably all sorts of "crap", for lack of a better word, that I don't even know about.
