Carbohydrates are the immediate energy source for the fish. Due to their carnivorous nature of the eons, fish tend to be poor at utilizing carbohydrate (Trout are utterly diabetic) so they may store it in the muscle or discharge it in the waste. This doesn’t change the fact that it’s important. It’s usually not listed as a percentage on most fish food labels. I am not attaching too much significance to it in this article.