Feeds which are typically formulated with an excess of protein are usually due to one of two reasons: either the protein is not very digestible so more has to be added to meet amino acid requirements, or excess protein is added because specific essential amino acid requirements are not known.
The excess protein provides a large margin of safety so that there will be less chance that essential amino acids are limiting in the diet. It is not economical or necessary to increase the total protein content of a feed to a point where excessive amounts of many amino acids are included in an attempt to meet the requirement for one or more of the essential amino acids that are shortest in supply.
A diet should be formulated based on digestible amino acid values of feed ingredients and an ideal protein.
The excess nitrogen excreted as ammonia by fish may have a negative impact on the environment because it is a major contributor to water pollution.
Because every species of fish and the individual proteins within each species has its own unique amino acid composition, the ideal situation would be to formulate a low protein feed that would minimize nitrogen excretion and at the same time meet all requirements for essential amino acids.
Today, in other species such as poultry and swine, this is done routinely since synthetic essential amino acids (e.g., methionine, lysine, threonine) are commercially available, and these animals utilize these synthetic amino acids efficiently.
A better understanding of the dietary nutrient requirements of cultured fish species and a continual search for accessible, highly digestible proteins to replace expensive fishmeal is essential. This approach coupled with applying the ideal protein concept in the formulation of fish feeds can greatly ameliorate nitrogen pollution arising from fish production systems and increase profitability.
The catfish and trout farms, which account for the vast majority of the food-fish produced in the United States, already have greatly reduced their use of fishmeal in feeds, to a total of around 5% in catfish diets, and a total of 20% in trout diets.
More information on the ideal protein concept is available here.
This material is drawn from document FA144, one of a series of the Department of Fisheries and Aquatic Sciences, University of Florida, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences. First Published: March 2007. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.