Quote:Originally Posted by rainforests1
It still doesn't answer my question. It may provide some benefits, but other food does as well. Why is it necessary?
Quote:Any complete diet must contain some protein, but the nutritional value of the protein relates directly to its amino acid composition and digestibility. The amino acid profile of fishmeal is what makes this feed ingredient so attractive as a protein supplement .High-quality fishmeal normally contains between 60% and 72% crude protein by weight. Typical diets for fish may contain from 32% to 45% total protein by weight. Another very important reason why fishmeal is sought after as an ingredient in aquaculture diets is because it contains certain compounds that make the feed more acceptable and agreeable to the taste (palatable). This property allows for the feed to be ingested rapidly, and will reduce nutrient leaching. It is thought the non-essential amino acid glutamic acid is one of the compounds that imparts to fishmeal its palatability.
Fish lipids are also highly digestible by all species of animals and are excellent sources of the essential polyunsaturated fatty acids (PUFA) in both the omega-3 and omega-6 families of fatty acids. The predominant omega-3 fatty acids in fishmeal and fish oil are linolenic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA). Essential fatty acids are necessary for normal larval development, fish growth, and reproduction. They are important in normal development of the skin, nervous system, brain, and visual acuity. PUFAs appear to assist the immune system in defense of disease agents and reduce the stress response. Fishmeal also contains valuable phospholipids, fat-soluble vitamins, and steroid hormones.
Such high digestibility of fish lipids means they can provide lots of usable energy. If a diet does not provide enough energy, the fish or shrimp will have to break down valuable protein for energy, which is expensive and can increase production of toxic ammonia. Fishmeal is considered to be a moderately rich source of vitamins of the B-complex especially cobalamine (B12), niacin, choline, pantothenic acid, and riboflavin.
Well, about that.Fishmeal in diets increase feed efficiency and growth through better food palatability and enhances nutrient uptake, digestion and absorption. The balanced amino acid composition of fishmeal complements and provides synergistic effects with other animal and vegetable proteins in the diet to promote fast growth and reduce feeding costs.
High quality fishmeal provides a balanced amount of all essential amino aids, phospholipids and fatty acids required for optimum development, growth and reproduction especially of larvae and broodstock. The nutrients in fishmeal also aid in disease resistance by boosting and helping to maintain a healthy functional immune system. It also allows for formulation of nutrient-dense diets, which promote optimal growth. 
Incorporation of fishmeal into diets of aquatic animals helps to reduce pollution from the waste water effluent by providing greater nutrient digestibility. The incorporation of high-quality fishmeal into feed imparts a 'natural or wholesome' characteristic to the final product, such as that provided by wild fish.