Aquaculture feeds characteristically contain a higher percentage of protein than feeds used in agriculture for poultry, swine and beef. A typical commercial production diet formulated for tilapia or catfish contains approximately 32-40 percent of protein, while one formulated for trout or salmon contains as much as 44-50 percent of protein, on a dry weight basis.
A commercial grower diet formulated for most terrestrial animals rarely exceeds 20 percent in total protein, and even for carnivorous species such as cats, the total protein rarely exceeds 38 percent. The use of higher protein levels in fish feeds is accepted because fish require less energy for maintenance of normal body functions than warm-blooded animals such as poultry, swine, cattle, horses, and other terrestrial animals.
Also, several species such as salmon and trout derive their energy from protein and fats more efficiently than from carbohydrates; similar to cats. Protein is typically the most costly nutrient in a formulated feed. Feed costs are usually the major operational expense in most aquaculture operations, typically ranging from 30-50 percent of the variable operating costs.
Protein in the majority of formulated fish diets worldwide depends greatly on fishmeal, which is more costly than high quality, plant-based protein sources, such as soy protein. Nitrogen in wastewater from aquaculture effluents is often considered a pollutant. In freshwater systems, nitrogen is sometimes a limiting nutrient, so adding it stimulates plant and algal growth. A majority of the excess nitrogen in either tank or pond product is formed during the breakdown of proteins and excess amino acids not incorporated into tissue by the fish.
The ideal protein can be defined as one that provides the exact balance of amino acids needed for optimum performance and maximum growth (e.g., size, carcass weight, yield, and body composition). When discussing the ideal protein concept, each of the amino acids in the feed is related to the requirement for lysine, which is one of the ten essential amino acids.
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