Pisciculture: What are the nutritional requirements for each stage

Those who are part of the fish farming business are already familiar with the three phases that make up fish farming: fingerling, rearing and fattening.

Each of these phases is composed of its particularities, requiring special handling and care for each of them. In addition, nutritional requirements should also be appropriate depending on the stage of cultivation.

For more appropriate control of each phase of the fish life cycle, it is recommended that the steps are conducted in different fish farms or well-defined and controlled environments, creating appropriate conditions for the development of the animals.

In this blog post, we will understand the characteristics of fingerling, rearing and fattening, and discuss how the fish should be fed in each of these phases.

We will also cover the breeding time of some of the main species and what determines the length of this period.

Fingerling: a critical phase that requires a lot of care

Fingerling is the first phase of fish development, which occurs when they are still young. This step is usually conducted in specialized farms to increase efficiency.

At the end, when they reach the ideal size and weight, they are sold to other fish farms or structures, where they will be submitted to the next steps – rearing and termination respectively.

In the larval phase, prior to fingerling, eggs hatch and fish, in millimeter size, do not structures need food, since they still have energy and nutritional reserves in their organisms.

Because of their size and fragility, they remain in incubators until they learn how to swim.

The larval phase varies by species, lasting for approximately one week for the main tropical fish. After this period, the fish enter the post-larval phase, in which they are counted and distributed to external hatcheries or intensive fingerling tanks.

Fingerling is a critical step, especially when it comes to food. At this point in life, because of the small size, there are few choices of organisms and feeds that fish can eat.

On the other hand, for the same reason, they end up being easy prey for aquatic insects. Unwanted fish species can also invade the hatchery, such as water snakes, water birds, among other threats.

In addition to that, fingerlings face food competition with tadpoles and other small fish.

Thus, fingerlings must necessarily feed on plankton, microorganisms that inhabit the water column, and benthos, microorganisms that inhabit the substrate. Except for some species such as tilapia, that eat inert food (ration) from the moment they open their mouths.

This type of feeding extends until fish are able to feed from other sources. This management is very common for native species such as tambaqui, painted, golden, among others.

The options for fingerling production

Some fingerling systems can be used, such as semi-intensive, intensive and extensive.

1) Semi-intensive fingerling production

In semi-intensive fingerling production, the most widely practiced system, hatcheries should have hydraulic devices for a complete flow control, which will allow a more optimized and adequate handling.

This system requires key parts such as total drying, mud removal, predator eradication, liming, fertilization to stimulate phytoplankton production and fertilization to stimulate zooplankton production.

Water quality must be regulated through physical and chemical analysis.

2) Intensive fingerling production

Intensive fingerling production, however, is a relatively modern system that is still under development in many fish farms. Its main goal is to create a closed system that prevents predators from entering.

This system should be laboratory driven and, because of its high level of control, it is more costly due to the constant need for human intervention.

The advantage, however, is the achievement of a high survival rate and, consequently, large production of fingerlings.

3) Extensive fingerling production

Another system under development is the extensive one. In this, family or community hatcheries receive the post-larvae animals (a phase prior to fingerlings). Here, the objective is to control the predator population before and during the process.

As disadvantages, extensive fingerling production can only be practiced with post-larvae fish of certain species and in lower density because there may be limitation of environment quality and availability of food organisms.

Also, depending on the characteristics of each unit, there is a difficulty in eradicating predators, as there is no way to control the flow.

Rearing: The ways to make the transition from fingerlings to juvenile fish

Reaching the ideal size to sell to other fish farms, the fingerlings go through the second phase of breeding, the rearing. At the end of this phase they will become juvenile fish.

This process can occur independently, that is, in fish farms that specialize in rearing fingerlings until they reach the juvenile phase, and then sold to other fish farms that will proceed to fatten/termination, or together with this third phase.

Thus, when the rearing is performed independently, the fingerlings are purchased directly from specialized hatcheries. After that, they are transferred to the rearing hatchery, where they will stay until they reach the juvenile stage. In the end, they are transferred once again, this time to the fish termination specialized farms.

Termination: the last phase before commercialize

At this stage, the fish will reach adulthood and then be directed to the consumer market.

In some fish farms, the ideal size to start the termination phase is 5 cm, but may vary greatly depending on species characteristics and seasonality. It is believed that this size ensures them a better efficiency to ingest larger particles, farinaceous, small insects, among others. In addition, they are also better prepared to escape predators.

Termination is a phase in which the objective is to increase the size of the fish until the commercial weight that varies depending on the species may exceed 5 kg.

Therefore, this step is characterized by the need for larger amounts of food.  That is, there is a greater need to adjust the treatment through daily food supply and regular monitoring of production.

The nutritional needs of fish

Some nutrients must be present in fish feed so that they develop healthily and grow well at all stages of breeding, especially with regard to the termination phase, the one where the diet is most reinforced.

The protein content will depend on each species and stage of the life cycle. Be aware that regardless of the protein source chosen, the 10 essential amino acids must be present.

They are:

• methionine;
• arginine;
• threonine;
• tryptophan;
• histidine;
• isoleucine;
• lysine;
• leucine;
• valine;
• and phenylalanine.

Choosing the protein source that will be part of the fish diet, however, can present its challenges. When using vegetable protein sources such as soybean meal, for example, it is usually necessary to supplement the diet with methionine, as these sources are low in this amino acid.

Animal sources are more preferable due to the complete amino acid composition. In addition, sources such as hydrolyzed chicken protein are produced through enzymatic hydrolysis, being easily absorbed and ensuring bioactive peptides that will promote extra-nutritional benefits to the fish organism, such as increasing the attractive palatability, antioxidant action, immunostimulant, among others for example.

Because they are related to growth, a higher protein content is usually more needed in the early stages of fish life.

Lipids, on the other hand, in addition to being energy sources and carriers of fat-soluble vitamins, also have essential fatty acids for fish development, such as eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA). These nutrients, the fats, are usually present in proportions ranging from 5 to 30%.

Carbohydrates are also a source of energy. However, unlike mammals, they are not efficiently used by most species, especially carnivores, the fish organism, and their excess is stored in the form of glycogen or fat.

In carnivorous diets, they should ideally be present at a maximum of 20% for optimal use by animals. Omnivorous species tolerate higher carbohydrate levels.

Water-soluble and fat-soluble vitamins help to improve fish’s immune system and some of them act as antioxidants. Minerals have the function of regulating osmotic balance and also help in the formation and integrity of bones.

Production time: the particularities of each species

The fish breeding stages are common to all species. However, each of them will present particularities throughout the process, which fish farmers need to be know about.

Tilapia, for example, is a freshwater fish considered one of the best for breeding. This popularity is due, among other things, to its fast breeding time, which usually ranges from 4 to 11 months, depending on location, climate, temperature, water quality and market demands.

The carp, in addition to requiring more delicate handling, has a higher average breeding time, around 1 year.

The catfish also has breeding time of approximately 1 year. Its reproductive peak occurs within 3 years. Most catfish has a predatory behavior because it has carnivorous eating habits. Added to that, it has a voracious appetite that makes it difficult for this species to reject any food offered.

Conclusion

The fish breeding stages are well defined and each one has its characteristics that must be respected in order to achieve healthy development and optimized growth.

To achieve this goal, production time needs to be considered, and special care must be taken with the animals’ diet so that all necessary nutrients are part of their diet.