Decreasing the Protein Level in Fish Feed

Protein is a major analytical component of farmed fish flour. Both technological progress and improved knowledge of the nutritional requirements of fish have allowed nutritionists to gradually reduce the protein content of fish feed without damaging its nutritional value.
 

The growth performance related to an animal feed is often directly linked to its protein content. Research shows that fish actually have a requirement for indispensable amino acids not for protein.  With this in mind, how can the amino acid composition of fish feed be adjusted in order to meet the exact requirements of the various fish species?

Only some amino acids (AA) are essential for fish growth

Amino acids (AA) are the basic structural components of proteins. They can be classified based on their chemical properties or their main characteristics (Figure 1).

• Non-essential Amino Acids can be synthetized by fish. There are 8 ”non-essential”  AAs.
• Essential Amino Acids (EAA) are those which cannot be synthetized by fish. These EEAs must therefore be supplied through fish feed.
• Semi-essential Amino Acids can also be synthetized by fish from  EAAs.

What are the consequences of an unbalanced protein profile?

The weight gain of an aquatic animal depends as much on the quality of the protein supplied by its feed than on its quantity. For fish, feed with an unbalanced protein profile has two negative consequences:

• It limits their growth. Liebig's law of the minimum, which states that growth is limited by the nutrient in shortest supply, applies to amino acids and proteins.
• Secondly, an unbalanced profile may result in redirecting AAs in excess to different pathways thereby triggering the production and excretion of ammonia in the fish pond.
  

The "ideal protein" can be defined as one that supplies the animal with all the essential amino acids needed in order to achieve maximum performance and growth. In fact, fish meal is the protein source that best meets the requirements of aquatic animals.

What is currently lacking is detailed knowledge of the requirement for essential amino acids of the all fish species. Tests conducted to this end have only been carried out on a limited number of species. Consequently, the only currently available solution is to make an empirical estimate of these requirements based on the established essential amino acid profile of known species. This  approach does not make up for the need to precisely assess an animal's actual requirements, but it has proved efficient so far in compensating for the lack of scientific information available on those requirements.

How can the feed formulation process take the requirements for essential amino acids of fish into account?

Protein-based nutrition of fish should first and foremost seek to ensure a sufficient supply of EEAs. It is the feed formulator’s task to evaluate and adjust the amino acid composition of the feed he/she produces. This goal can be achieved by various means:

• Access to comprehensive data bases: these data bases provide information on the amino acid composition of each of the available raw materials.
• Access to feed specifications: each ingredient corresponds to a set of maximum/minimum dietary feed constraints to be respected. These will allow the formulator to adjust the composition of his/her feed;
• Access to analytical laboratories: detailed analysis of raw materials allows the feed formulator to check the quality of these materials.
• The formulator can also incorporate synthetic amino acids in feed formulation.

From a formulation strategy perspective, the nutritionist’s task is then to adjust the protein level of the feed by composing with complementary compositions of raw materials and the amino acids available.

Amino acid requirements are likely to vary depending on the species of fish, their environment, their physiological state, etc. With detailed knowledge of raw materials and nutritional requirements of fish species, TECHNA Group experts can assist feed manufacturers in their formulation process and setting of adapted linear programs. For further information please contact us!