Formulation of diets for fingerlings and fry fishes
Fish species have special nutritional requirements due to the particularities of their digestive system.
Specificities of herbivorous species
The diets administered in aqua production are especiallyÂ designed depending on the needs of the target speciesÂ so that they supply the essential nutrients for fish to grow properly and remain healthy.
These needs vary broadly depending on the target species and productive stage. This is because theÂ nutritional requirementsÂ are different for each species and because of theÂ singularities of the digestive tract.
Specificities of the digestive tract in fishes depending on their feeding habits
Generally, species with more specialized feeding habits, the carnivorous and herbivorous, produce a lesser variety of enzymesÂ and these are less active. In these cases, it is necessary to include enzymes in the diets to make sure they are used properly.
On the other hand, fish with varied diets in nature, such as omnivorous fish or other species whose habits change as they develop, can secret a greater diversity of enzymes,Â so that they can more easily adapt to all types of diets.
The anatomy of the digestive tract is also adapted to the type of diet, so that theÂ species that are mainly herbivorous, such as common carp,Â have a more developed intestine and a smaller stomachÂ than carnivorous species.
Herbivorous speciesÂ have a small stomach, which means that they cannot ingest large amounts of feed, since the fullness stomach regulates the appetite; and a very long intestinal tract, which means that it needs more time to digest feed. Therefore, theyÂ need to be fed continuouslyÂ as they are constantly digesting the feed. The ideal frequency to administer feed varies depending on the development phase, too, since the first ages need to be fed continuously, while juveniles and older fish require lower feeding frequencies.
Nutritional composition of the diets for herbivorous fishes
The protein requirements in herbivorous species are between 30 and 40% of the diet in dry matter, far from the 40-55% required in carnivorous species . Besides, the protein ingredients in diets for herbivorous fish are usually of plant origin, since they tend to have fewer problems than carnivores with this type of protein sources. This represents an advantage over carnivorous fish farming because vegetable protein is usually more economical and sustainable , .
CarbohydrateÂ levels in omnivorous or herbivorous fish dietsÂ can be high, as these species are more tolerant to high levels of these compounds. Otherwise, the inclusion of lipids is usually low, in carp it should be below 6%, since these fish do not usually tolerate high levels of triglycerides and they can lead to fatty carcasses.
|Species||Crude protein (%)||Crude energy(kJ/g)||Protein:energy rate|
|Common carp (Cyprinus carpio) adult||>25||12.8-22.7||15.3-29.6|
|Tilapia (Oreochromis aureus) fry||34-36||13.4||20.5|
|Tilapia (Oreochromis aureus) juveniles||56||19.3||27.5|
|Hybrid tilapia (O. niloticus x O. aureus)||30-35||17.3||30.3|
|Nile tilapia (O. niloticus)||25-35|
|Milkfish (Chanos chanos) juveniles||40||15.3||26.3|
|Rainbow trout (Oncorhynchus mykiss)||40-45||19.1-20.8||20.5-22.5|
Table 1.Â Requirements of protein, energy, and protein/energy rate in different species. Carp is considered mainly herbivorous, Nile tilapia an omnivore, milkfish a planktivore and the rainbow trout a carnivore. Protein levels are higher in first ages and decrease in older stages. Source: .
Regarding the ingredients used, diets usually containÂ cerealsÂ as a source of energy (corn, barley, wheat),Â sunflower or other vegetableÂ oilsÂ as a source of energy and triglycerides, andÂ protein sources of vegetable originÂ such as soy flour.
Some diets intended for omnivorous but mainly herbivorous fish may also containÂ fishmeal, MBM, or feather mealÂ to increase the protein content in the feed.
Lastly,Â enzymes like carbohydrasesÂ (such as xylanases and amylases) are highly recommended in herbivorous species because the pH in their digestive tract is more basic and, under these conditions, carbohydrases are more active. Proteases like pepsin are recommended if high protein diets are administered in adult herbivorous fish. Proteases are more active at an acidic pH and in species with larger stomachs, so they are less effective in herbivores.
Enzyme supplementation is a common practice that is more frequent in larval stagesÂ and early stages (fry and fingerling) when the endogenous synthesis of these enzymes is not sufficient for proper feed digestion.
Ingredients of vegetal origin: limitations in carnivorous species
One of the priorities of the poultry industry is toÂ improve the sustainability of production, and this more achievable when growing herbivorous species, as theyÂ do not require animal proteinÂ in their diets. In other words, herbivorous fish are ultimately more efficient converters of plant protein to fish meat.
This way, it is easier to use protein vegetal sources such as soybean, instead of fishmeal or fish by-products that lead to the exploitation of rivers and seas. In contrast, carnivorous species such as salmon or trout require relatively higher amounts of resources.
Moreover, these speciesÂ tend to require less investment for their cultivation and are more affordable for the general population, compared to salmon, because the latter requires highly concentrated protein feed and very specific rearing conditions.
Despite this, herbivorous fish farming currently represents only 5% of the total fish reared in aquaculture, probably since they are species that are less appreciated by consumers and with less value in the market.
You may also be interested in:Â Veterinary equipment and vaccination in animal production
Diets intended forÂ herbivorous fish speciesÂ require a lower content of protein and have higher carbohydrates inclusions. Besides, these species are more efficient in converting vegetal protein to animal protein, which means that their diets can be exclusively based in ingredients of a vegetal origin.
To optimize feed digestion, especially during the first development stages when the digestive system is not yet completely developed,Â carbohydrasesÂ can be used to help to digest carbohydrates.
Global Vetâ€™s LabÂ offers aÂ feed analysis and formulation serviceÂ to optimize feed composition while considering the inclusion of the best functional additives. To use the service, please contact us through our webpageÂ www.globalvetslab.com/enÂ or via email atÂ email@example.com
- P. G. White, T. A. Shipton, P. B. Bueno, and M. R. Hasan, Better management practices for feed production and management of Nile tilapia and milkfish in the Philippines, no. September. 2018.
- M. R. Hasan, â€śNutrition and Feeding for Sustainable Aquaculture Development in the Third Millenium,â€ť in Technical Proceedings of the Conference on Aquaculture in the Third Millenium, 2000, pp. 193â€“219.
- GVL, â€śFuentes alternativas de proteĂna en crĂa de peces carnĂvoros. Uso de enzimas.,â€ť Global Vetâ€™s Lab, 2021. [Online].
- NOAA, â€śFeed for Aquaculture,â€ť NOAA Fisheries. [Online]. Available