Date: 02/07/2020

In aqua nutrition, palatability is an important aspect to be taken into account when formulating feeds, considering that this characteristic is intrinsically related to digestibility.

More palatable feeds – because they are more attractive to animals – result in greater consumption rate. On the other hand, when this characteristic is not present, there is an accumulation of residues in breeding grounds, due to uneaten/digested food, negatively impacting the water quality of the breeding environment.

With a poor diet, aquatic animals will have a performance decrease due to reduced growth.

Therefore, palatable feeds are capable of bringing benefits to animals and also to aquaculture farmers, since they allow the reduction of expensive components in the animals’ diet, such as proteins, for example.

In this post, we will discuss the impact of palatability on the nutritional aspects of aquatic animals, as well as ways to ensure this characteristic in aqua formulations.

Palatable feed ingredients

The ingredients commonly used to formulate aqua feed are rich in amino acids, nucleotides, amines, and nucleosides. Some examples are fishmeal and shrimp meal.

Despite the nutritional potential of these ingredients, the high palatability, and guaranteed performance, they have a high cost due to low availability.

An aqua feed based on fishmeal represents from 40 to 70% of the operational costs of aquaculture, according to an article published in the Multidisciplinary Digital Publishing Institute (MDPI). Therefore, the search for alternative ingredients that can be part of the feed – reducing the cost while being able to maintain the same level of performance – is one of the great challenges of this industry.

According to a study of the University of Guelph, ingredients of animal origin, such as by-products of chicken slaughter, are highly available and have a lower cost. In addition, they are highly digestible protein sources, rich in essential amino acids, vitamins, and minerals.

The inclusion of this type of element in feeds also contributes significantly to a more sustainable industry, since by-products are re-added to the production chain instead of being discarded.

In this sense, hydrolyzed proteins are great examples. Resulting from the solubilization of proteins – either by chemical (acid or alkaline) or enzymatic hydrolysis – they are broken down into amino acids of lower molecular mass, therefore, more easily digestible by the animal organism.

Among the options available, enzymatic hydrolysis has the advantage of low environmental impact due to the non-use of harmful solvents.

In addition, the enzymatic specificity in breaking down proteins generates bioactive peptides that strengthen the animals’ immune system, positively impacting performance due to increased digestibility.

Reducing costs without losing palatability

Chicken Protein Hydrolysate (CPH), produced by enzymatic hydrolysis, has already proven to be effective in an experiment carried out in Vietnam. There was a replacement in diets for tilapia, being changed from 10% fishmeal to 4% of CPH. As a result, it did not affect negatively the palatability. Consequently maintaining weight gain at the same rate as the control diet and without causing any loss in performance.

In addition, CPH also showed satisfactory results in experiments carried out in Brazil, with the substitution in aqua feeds from 2% fishmeal to 2% CPH, showing a 23% improvement in weight gain.

In another study, published in the MDPI, the addition of 5% Chicken Protein Hydrolysate, liquid swine hydrolysate, feather protein hydrolysate, and swine mucosa hydrolysate was used in an aquarium for Nile tilapia. As a result, all hydrolysates had satisfactory palatability indexes and the CPH improved the palatability index by 10.82% compared to the diet with a 5% inclusion of fishmeal.

It is interesting to note in this study that the fish presented a higher percentage of consumption for the diets with the addition of co-products of the agribusiness when compared to the diet that contained only fishmeal.

In an Aquaculture Reports survey, where the replacement of fishmeal with chicken feather meal was studied, the addition of 50% of the alternative ingredient made the palatability index rise from 15.27 (control diet, only with fishmeal) to 21.41 in the diet of the fish Sparus aurata.

These results show the enormous potential presented by protein hydrolysates, which in addition to being an alternative to lower the price of feed, can even increase the performance of different aquatic species.

Important aspects when replacing ingredients

Aquaculture feed should have a balanced nutritional composition that is attractive to animals. However, the protein, lipid, and starch content of food are relative. This is true not only depending on the species and their life cycle, but also considering factors such as the place where animals are raised and environmental restrictions, for example.

In the Rendered Products in Fish Aquaculture Feeds study held at the University of Guelph, they show that the protein content is quite variable in most ingredients. This variation may be due to the source and quality of the ingredients applied, but also due to differences in the extraction methods used.

In the same study, there is an indication that foods formulated to contain up to 30% protein in poultry by-product meal supported excellent growth performance in rainbow trout (Oncorhynchus mykiss). This is because the protein present is very similar to fishmeal in nutritional terms. In addition, this ingredient can effectively replace all fishmeal in this animal’s diet without a negative impact on performance.

In contrast, the substitution of crude protein from flame-dried blood meal showed protein digestibility of only about 12%, while protein from spray-dried blood meal was almost completely digested. This reinforces the importance in the selection of the raw material and how the production process can influence the digestibility and other characteristics of the ingredient.

However, some aspects require more care. Researchers indicate a low digestibility for the protein of the meat and bone meal of lamb and of beef in the fish of the species Bidyanus bidyanus. The authors suggest that proteins from ruminant animals are generally less digestible by fish.

Overall, the Rendered Products in Fish Aquaculture Feeds study held at the University of Guelph indicates that the vast majority of processed animal proteins produced using modern manufacturing practices (such as enzymatic hydrolysis) are highly digestible by fish.

Therefore, in order to formulate nutritious and successfully accepted aqua foods, it is necessary to add ingredients with high digestibility and that are produced with quality raw material. In addition, it requires an understanding of the nutrients needed by the animal, the bioavailability, the tolerance, the interaction between nutrients, and the palatability.

As already demonstrated, chicken protein hydrolysate has a good performance when applied in aqua diets. For this reason, it is worth mentioning that for the preparation of an adequate formulation of aqua foods, it is important to have reliable suppliers, who produce the ingredients with quality raw materials, through efficient extraction methods, and within the required standards.


The formulation of aqua feeds must take into account palatability. By controlling this characteristic, it is possible to reduce the amount of waste and even improve the growth and performance of aquatic species.

The partial replacement of fishmeal by ingredients from the agribusiness has been presented as a sustainable and economically viable alternative to reduce the costs of food in aquaculture without losing quality and improving the palatability of the feed.

Chicken protein hydrolysate proves to be a great alternative for application in aqua foods. However, it is important to have a formulation with a variety of quality ingredients that have a nutritional composition, digestibility, and palatability according to the animal’s needs.