Date: 26/05/2021

In order to formulate feed and choose ingredients for fish farming nutrition it is essential to consider not only the quantity of protein necessary for a balanced diet, but also the quality of this component. This is because the composition of this nutrient can directly affect digestibility in aquaculture.

Digestibility, in turn, affects the nutrition, health, growth and development of the animals. Furthermore, low digestibility in aquaculture can interfere in water quality due to debris that can accumulate in the environment.

In order to maintain productivity and reduce production costs, the best strategy is to choose ingredients that can be scientifically proven to be nutritionally efficient and to increase digestibility in aquaculture.

Being aware of both the concepts and new developments in the market is the best way to go for those who want to carry out intelligent and sustainable ingredient substitutions and optimize the formulation of animal feed, producing better yields.

Digestibility in aquaculture

Digestibility is a factor that determines the ease with which an ingredient can be digested by an animal’s system. That is to say, an ingredient with high digestibility will be better exploited by the digestive system, having its nutrients and amino acids absorbed and used to the benefit of the health and nutrition of the animal.

Digestibility can differ, not only in accordance with the type of food, but also according to the species of animal that is being fed. This being the case, digestibility in aquaculture needs to be appraised according to the species and how the species is being raised.

Digestibility coefficient tests will determine how a particular ingredient is exploited by the species in question. Knowing these values is of the utmost importance for feed formulators, who can thus base themselves in these coefficients in order to choose basic ingredients according to how much value for money each one provides.

The importance of digestibility in fish farming nutrition

Unlike other types of animal husbandry, such as pigs and pets, digestibility in aquaculture presents a further significant factor beyond nutrition: water quality in the production environment of the animals. When this environment is unbalanced, the growth and development of the animals is impacted, and the rates of death and disease increase.

Offering a highly digestible, protein rich diet is fundamental if we want to maintain productivity. This is because, aside from being a more expensive primary ingredient, excessive protein in feed causes a significant increase in nitrogen excretion. This element, combined with phosphorous excretion, is the principal cause of eutrophication of the aquatic environment.

With the aim of developing feeds with ideal characteristics for consumption, nutrition and the sustainability of the farmed area, research and development organizations have tested more functional, cost-effective, balanced, and complete alternative main ingredients for feed formulation.

Despite fish not having a direct need for protein, they depend on essential amino acids for their vital functions to work. For this reason, beyond just giving them sources of protein, it is necessary to pay attention to the quality of these nutrients and to the presence and digestibility of amino acids and other feed elements.

In this context the concept of an ideal protein has been used, considering the need for amino acids in fish farming nutrition. This being the case, the best decision for feed formulators is to choose ingredients that offer all the necessary amino acids, with high digestibility.

Factors that affect digestibility

Digestibility in aquaculture can be affected by various different factors. Among the main ones we can highlight:

Size and age of the animals

The age of animals may interfere in digestibility due to their size in the different phases of their raising and production.

The article Factors that affect digestibility coefficients in feed for fish , in the Nutritime electronic journal, shows that, in herbivorous and omnivorous fish species, digestibility is influenced by the size of the fish as a direct result of the relative increase in size of the animal’s intestines.

This factor causes digestion to take longer and the time for assimilation and absorption of nutrients also increases. It is worth pointing out that these assessments did not show changes in digestibility related to the weight of the animals, but to the actual size of them.

Water temperature

Species such as fish are poikilotherms, or cold-blooded. This characteristic means that water temperature also influences the digestive functions of these animals.

This is because variations in water temperature impact the fish’s entire system, altering food consumption, enzymatic activity and the rates of digestion and absorption of nutrients.

According to the article Factors that affect digestibility coefficients in feed for fish , a rise in temperature, within the ideal margins for the animals, can raise the digestibility coefficient.

Feed processing

The type of processing feed has undergone can also improve or worsen its digestibility. This is because processes such as grinding, peletizing and extrusion can alter the chemical and physical properties of ingredients.

The article Factors that affect digestibility coefficients in feed for fish reveals that foods that have undergone a process of extrusion can show improved digestibility coefficients, especially as related to the gross energy content.


Palatability also exerts a strong influence on digestibility and on water quality in the farming environment of animals in aquaculture. Palatability represents how attractive feed is to animals, causing them to want to eat it due to characteristics such as texture, flavor and smell.

When animals receive feed with low palatability, the tendency is for them to reduce or interrupt their feeding, which increases the accumulation of waste and debris in the water and can lead to nutritional deficiencies.

For this reason, investing in ingredients with high digestibility and palatability is the best way to guarantee that animals’ nutrition will be balanced and that they will benefit in a real way from beneficial additives.

The importance of essential amino acids

Amino acids are responsible for protein synthesis in the systems of aquatic animals. The synthesized proteins will carry out functions such as the catalysis of biological reactions and building muscle tissue.

When a high quality protein (rich in amino acids and completely available for digestion) is added to feed for fish farming, the quantity of feed necessary to fulfill nutritional needs is lower. This means that costs are reduced and the environment remains free from accumulations of waste and excretions.

Of the 20 existing and available amino acids, 10 are essential for the growth and development of aquatic animals. These are: arginine, histidine, isoleucine, leucine, lysine, metheonine, phenylalanine, threonine, tryptophan and valine.

The absence of these elements can cause problems such as anorexia, reduced growth and anatomical problems in the animals. It is also important to note that every species presents different needs in terms of the quantities of each amino acid, and that each amino acid shows different digestibility coefficients.

For a balanced diet for tilapia for example, the study Innovations in the use of industrial amino acids in Nile tilapia diets , from the Brazilian Journal of Animal Husbandry, shows that metheonine should represent 55% of the sulfur containing amino acids in the formulation. While lysine should represent levels of 5.5 to 6.5% of the total protein.

Professionals responsible for the formulation of quality feed must study and analyze deeply the values to be considered. In this way it is possible to choose key ingredients and maintain good profits.

How to improve digestibility in aquaculture through quality ingredients

An ingredient which presents excellent digestibility and palatability rates is fish meal. It is not only attractive and easily digested, but it also guarantees a balanced diet with good productivity potential in aquaculture.

However, the low availability of this ingredient makes for a notably high cost, representing around 40 to 70% of costs in aquaculture. With studies and tests carried out by companies in the agriculture sector, it is currently possible to find substitutes that maintain nutritional qualities while being more economically viable.

Animal based ingredients, such as byproducts of chicken slaughtering, are rich sources of highly digestible, palatable and sustainable proteins and amino acids. Due to their high availability these types of basic ingredient offer good value for money in fish farming nutrition.

Among the available products on the market that present this high efficiency, we can highlight poultry offal meal, feather meal, and Chicken Protein Hydrolyzed.

Poultry meal

Poultry meal offers all the amino acids necessary for good development of aquatic animals, and can substitute fish meal either partially or totally without negatively affecting the performance of the animals. In the case of carnivorous fish, Low Ash Meal is an even more efficient alternative.

As well as being highly palatable, Low Ash meal offers high levels of protein and energy, very similar to those of fish meal. The study Evaluation of poultry by-product meal in commercial diets for hybrid striped bass analyzed the digestibility of these nutrients and demonstrated that substituting 35% of the fish meal with chicken byproduct meals promoted a similar performance to that of fish exclusively fed with fish meal.

Feather Meal

Feather Meal also shows an equivalent level of efficiency to fish meal in studies, and is thus a cheaper alternative for producers who want to improve their returns in aquaculture.

The study Feather meal for fish feed , in International Aquafeed Magazine analyzed the feeding of tilapia and shrimp. The group that received feed based on feather meal showed no negative effects compared to the group that was fed fish meal.

However, in order to guarantee the performance of feather meal, it is important to note that formulators need to prioritize the quality of the basic ingredients to be added to the feed.

Choosing fresh basic ingredients from a known source is the best way to guarantee the quality of the final formulation and the benefits of substituting with this lower cost ingredient.

Chicken Protein Hydrolyzed (CPH)

Enzymatic hydrolysis has gained notice in the market due to its efficiency in reactions and the improvement in nutritional performance and digestibility. Among the available options Chicken Protein Hydrolyzed has been more and more explored and studied for the improvement of animal feed.

One can find CPH with excellent rates for fish farming nutrition, with minimum levels of raw protein of 75% and minimum digestibility in pepsin, of 90%.

A study carried out by the State University of the West of Parana showed that including CPH in the diet of Nile tilapia increased palatability by 10% when compared to the control group which was given fish flakes.

As well as being digestible and palatable, CPH also acts positively in the preservation of water quality. This is because the easily digested proteins avoid excessive Nitrogen and Phosphorous excretions in the farm environment.


Ensuring digestibility in aquaculture means ensuring animals will be completely and satisfactorily fed in order to complete their development phases with high productivity and quality.

Choosing optimal ingredients, rich in the necessary elements, goes well beyond analyzing characteristics such as the protein content, but also involves analyzing the quality of that protein and how it will practically benefit production.

Foods with a high protein content won’t always fulfill the objectives of a diet for aquatic animals, since they can be wasted – depending on the energy use of the animal. For this reason prioritizing ingredients that have been scientifically proven to work and made with fresh basic ingredients is the best solution for someone who wants to reduce costs, improve on performance and guarantee the cost effectiveness of fish production.