When we think about nutrition for fish, several studies are carried out to know and understand how to apply the best methodology in production, to obtain maximum gains in zootechnical and economic results. To do this, it is necessary to find and define nutritional requirements for each species of fish.

Within this study, in the popular first question regarding parameter assigned to fish feed is the value of protein, and within this context we have to understand and direct all attention to the levels of essential amino acids that will make up the diet with the aim of obtaining the best result in the growth of the species.

Today much is said about crude protein and/or total amino acids, however, the best way to qualify and quantify a feed is through the digestible protein, or rather, digestible amino acids in the formulation.

Regarding proteins, amino acids can be highlighted. Knowledge of its digestibility in the ingredients used is essential to consider a product with maximum efficiency that will bring both environmental benefits, emitting less residue of substances via excreta, and promoting better performance in the animal, and it is also essential that the assessment of cost versus benefit is technically viable.

For protein composition, the sources available for use in the fish feed diet are: soybean meal, peanut meal, fish meal, chicken offal meal, hydrolyzed feather meal, meat and bone meal, blood, hemoglobin, corn gluten, corn DDG and others.

Linked to this condition, it is essential to know the raw materials and their suppliers so that the product follows as established in the nutritional matrix of the formulation program. Within the same type of ingredient we can have different prices and different qualities, such as meat and bone meal.

O second parameter What we must observe is the level of ethereal extract or fat, which is an excellent source of energy for fish and which, together with carbohydrates in the diet, makes up the energy part.

You carbohydrates they contribute to the performance of animals in their productive activities and as some of these ingredients contain starch in their composition, they also help in the feed production process (extrusion).

With this attribution, we can highlight a wide range of inputs, such as: corn, sorghum, millet, wheat bran, rice grits, rice bran that help to make up the energy part of the ration.

There is one optimal energy:protein ratio in the formula and so that there is no imbalance in the consumption and absorption of nutrients and impair the performance or accumulation of fat in the animal, attention must be paid when producing the feed so that the amount of fat and carbohydrates does not cause an imbalance in the energy relationship: ideal protein.

Some protein ingredients contain a good amount of fat that helps in the composition along with the addition of soybean oil, fish oil, chicken oil, etc. Maintaining this balance, the fish will have good muscle formation and/or good fillet yield, with low accumulation of body fat.

The addition of appropriate amounts of vitamins and minerals -vitamin-mineral premix- in diets complements the nutritional requirements of each species and can contribute to the best development condition of the fish, by optimizing nutrient absorption and contributing to the animal's physiological processes.

Other parameters should also be mentioned as crude fiber, which is characterized by the amount of fiber that makes up the formula. As the majority of fish species produced are not herbivorous, it is essential to pay attention to their inclusion in feed so that a high amount of fiber may not interfere with digestibility. It is important to always understand the capacity of the species that will be cultivated in order to maintain the optimum level for optimal movement and intestinal health. 

A mineral matter (ash) It is what is left over in the process and ends up not being used by the body, and therefore the lower the value of this item in the laboratory report, the better the quality of the product.

Already the moisture is another item always observed on the labels and for good product stability in storage it is necessary that it does not exceed 10-12% of humidity, to avoid loss of feed due to mold and mildew in the field.

There is still a need to better understand the raw materials and the suppliers' products in more detail to have parameterized the main choice indices in the food strategy.

When we have accurate data, it becomes clearer which path or strategies to follow. An example of this is that the additive will reach its maximum economic potential when we know how to use it to enhance nutritional gains.

Additives must be used with knowledge and closely based on the food and/or environmental strategy to optimize production, in addition to following the regulations of the Ministry of Agriculture, Livestock and Supply (MAPA) under normative instruction 13/04 (amended by normative instruction no. ◦ 44/15). It is also important to demand from additive suppliers clear information about the product and the analyzes necessary to guarantee its effectiveness.

Within this context, our main challenge is to understand what problem the animal will be exposed to, taking into account the cultivation phase, the production system and the time of year. Having this knowledge will help you to include the correct additive and in the indicated inclusion to minimize the challenge or problem caused by sanitary or even management factors.

There are several types of additives, as illustrated in Table 1, each with its own specificity and therefore it is important to understand and be clear about the best strategy for applying them in the field.

Table 1. Additives used in animal diets.  

Source: Adapted from CAVALHEIRO et al. (2014).

When we think about different usage strategies, we can think of different forms of application such as:

• Zootechnical and anticoccidial additives: use preventively.
• Technological and nutritional additives: they have an action to optimize nutrition and must be used regularly, contributing to an improvement in the results of zootechnical indices.
• Probiotic additives: it is necessary to have knowledge of their mode of action and understand the differentiation between them, as illustrated in Table 2.

Table 2. Basic differences between probiotic, bioremediating and biocontrolling microorganisms.

Source: Adapted from MOURIÑO et al., 2012.

Another line of additives that can be used to help with health challenges are essential oils, nutraceuticals and/or plant extracts, as described in Table 3:

Table 3. Plant extracts and properties:

Source: Adapted from SANTOS et al. (2009b).

Thinking about the line of products that help with intestinal health, we have the important role of yeast, which can come from sugar cane, beer and bakery substrates. This class of products is part of nutrition as a component to increase the amino acid profile and, depending on the type of process carried out, can help with intestinal health, acting as prebiotics.

When we move towards a more specific objective, we can work with concentrated products where the main components are: beta-glucans, mannan oligosaccharides and nucleotides.

 Table 4. Yeasts and their derivatives.

Source: Aleris 2020.

In short, when we carefully evaluate production and are aware of the challenges faced on a daily basis and seek to advance knowledge, available technologies and tools can minimize the harmful impacts that occur in fish farming.