Gentlemen,
In case it hasn't been addressed here, and my apologies if it has, what about carbohydrates? According to a feed researcher at Purdue, Dr. Paul Brown, carbs are the big fatty deposit maker. Furthermore he says too many carbs makes fish into functional diabetics whatever that means.
Spot on. In humans, processed/refined carbs are the number one cause of obesity. That's because they stimulate high secretions of insulin to store all the glucose, and too much insulin for too long leads to insulin resistance. Insulin resistance leads to obesity and diabetes.
I'd wondered about this before, since we now know that fat per se does not cause us to get fat. One very recent study showed that skim milk consumption is far more correlated with diabetes than whole milk, for instance. However, the digestive system of a fish is different than a mammal, so I wasn't sure what hurts us would hurt fish.
Apparently it does.