The same with water. The less water, the better. Water in frozen foods is a combination of the water present in the tissues of the frozen animal and the water used to prepare it for freezing. Food coloring is also listed. Fast, active, fish such as many tetras, danios, damsels, etc., need more protein than do more sedentary fish such as many catfish, hawkfish, etc.
Protein is burned up as calories in exercise.
Fish also need more protein for egg production. If you want to spawn fish, feed them a high-protein diet. Temperature plays a large part in how fast a fish metabolizes protein. Fish kept at higher temperatures need more protein than do the same fish at lower temperatures. You can see why there is really no hard and fast rule here.