For aquatic animals, more important than the protein content required in the diet, is its quality. But how do you measure the quality of a protein to use in aquaculture?
For monogastric animals, such as fish, it’s important to be aware of the amino acid sequence that constitute this nutrient. A protein that has all the essential amino acids and is highly digestible can be considered of high quality.
Therefore, to develop feed for aquaculture, it is necessary to know in depth the available protein sources and understand the importance of each amino acid in it.
In this blog post we will discuss how each amino acid affects the health of aquatic animals, which ones should be present in the feed and which protein sources have the most advantages.
Essential amino acids: the key to high quality proteins
In fish, shrimp and other aquatic species, the role of amino acids in the diet is to work as the basic unit for protein synthesis. Proteins, in turn, once synthesized, will participate in various functions in the body, such as muscle tissue construction, catalysis of biological reactions (enzymes), among others.
Giving low quality protein to animals is extremely harmful to the profitability of aquaculture and the environment.
To overcome the poor quality, the animals end up consuming more protein than necessary for growth, making an impact on the costs related to feeding. On the other hand, when high quality protein is introduced in the diet, the amount needed to meet basic needs is lower.
Of the 20 amino acids available in nature, 10 are considered indispensable for the diet of fish and other aquatic animals. Since they are not synthesized by the body, or not synthesized in enough quantities, they must be acquired through diet.
They are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Cysteine and tyrosine are semi-indispensable as they can only be synthesized from their methionine and phenylalanine precursors.
In the absence of these amino acids, there is a reduction in the growth of animals, and they may present anorexia, besides anatomical signs of such deficiency.
To keep the survival rate constant, one must be careful about the amino acid profile of the protein source, especially regarding the presence of the 10 essential substances. Usually they should represent about 40-60% of the total protein in the diet of different fish species.
One protein source that meets these requirements and is therefore widely used in feed intended for aquaculture is fishmeal. In addition to this ingredient having all essential amino acids in the optimal proportion, there aren’t anti-nutritional factors and it has high digestibility and palatability.
Why do alternative protein sources need to be considered?
Fishmeal has low availability, which directly affects its cost. Due to this factor, the use of this protein source ends up being economically unfavorable to aquaculture, forcing the industry to look for quality alternative sources that are more available and economically viable.
There are four categories of ingredients that can be used as a protein source. They are: ingredients of terrestrial animal origin, fish meal, plant sources and single-celled organisms.
Of these, the ingredients of terrestrial animal origin, such as swine and poultry, are noteworthy because of the high content of high quality protein.
The ingredients made from hydrolysis are examples, which besides being high in protein, have all the characteristics necessary to be considered of high quality. They also have bioactive peptides, obtained by the enzymatic hydrolysis process. These peptides have antioxidant activity, antimicrobial, immunostimulants, among others, being able to minimize the damage caused by the oxidation process in the animals’ organism and improve the resistance.
Some protein sources, mainly of plant origin, in addition not having all the necessary amino acids, have antinutritional factors as well. In this case, to be used without harm to animal health, a combination of two or more sources must be made to address the deficiencies.
For each species, a different requirement
When developing aqua feed, it is necessary to be aware that each species has different requirements related to each amino acid. In the tilapia diet, for example, it is estimated that methionine should account for about 55% of total sulfur amino acids.
On the other hand, lysine is one of the most limiting amino acids in fish diet, and it should be present in the proportion of 5.5 – 6.5% of total protein.
Using lysine as a parameter, the requirement for optimal tilapia growth over other amino acid types is calculated based on the percentage of lysine:
- Arginine: 86%
- Histidine: 34%
- Isoleucine: 62%
- Leucine: 68%
- Phenylalanine + Tyrosine: 111%
- Threonine: 79%
- Tryptophan: 20%
- Valine: 56%
- Methionine + cystine: 79%
As we can see, these are very specific values, so they should be considered by the professionals responsible for producing high quality feed.
In order to develop high quality aqua feed it is essential to understand the dietary needs of each species individually, especially regarding the sources of protein and essential amino acids. Thus, an adequate diet will provide a high rate of survival and health for the animals, in addition to optimized growth and performance as a whole.
Considering this, hydrolyzed proteins, especially the animal origin ones such as chicken protein hydrolysate, are great alternatives for application in the feeding of aquatic animals. This ingredient, in addition to being more economically viable, has an adequate balance of essential amino acids, high digestibility, palatability and the presence of bioactive peptides.
It is worth mentioning that it is important to have reliable suppliers that guarantee product quality, through traceability, using fresh raw materials and that have an enzymatic hydrolysis process, as this method preserves the composition of amino acids and generates bioactive peptides. In this way, when the desired characteristics for this reliable application are reached, the production systems in aquaculture gain a great competitive advantage.