In aquaculture, as in the rest of animal productions, feed is one of the main production costs, amounting to 60% of the total productive cost.

There is a great diversity in relation with the nutritional needs of the different aquaculture cultivated species. This diversity derives from differences in the environment in which they live and the different types of feeding habits. Freshwater and seawater, surface and benthonic, as well as carnivorous, herbivorous and omnivorous feeding species are cultivated.

This article reviews some of the main nutrients of interest in aquaculture.

1. Carbohydrates

While carbohydrates (sugars and starches) are the most important source of energy for terrestrial animals (mammals and birds). Their role in aquaculture nutrition is not so important due to the limited the capacity of these animals for their digestive and metabolic use.

However, they are the most economical source of energy that we can use in the nutrition of all species. Even though they do not represent an essential element, they are added in the formulation to reduce production costs and because they contribute to the physical shaping of the pellet and its stability in the water. In addition, starches get good results in the extrusion process for floating feed.

The digestibility of carbohydrates depends on the type of diet: herbivorous and omnivorous fishes use carbohydrates more efficiently compared to carnivorous fishes. It also varies with the complexity of the molecule, increasing when its molecular weight decreases. The digestibility of complex glycides can be increased by applying heat treatments.

Fishes store carbohydrates as glycogen, which will be easily mobilized when energy is required, although its use is not as efficient in fish as it is in mammals. Mammals can extract 4 Kcal per gram of carbohydrate compared to the 1.6 Kcal that the fishes extract.

2. Vitamins

Vitamins are organic compounds essential in fish diets for their normal growth and health, they should be administered in the diet as fishes are not able to synthesize them. Within the water-soluble vitamins, vitamin C is the most important in fish nutrition for its antioxidant and immunestimulant effect. Deficiency of ascorbic acid (vitamin C) will cause scoliosis, while folic acid (vitamin B9) deficiency will cause a dark coloration. Regarding fat-soluble vitamins, vitamin E is of a greater importance also because of its role as an antioxidant.

The vitamin requirements in cultured aquaculture species are highly variable depending on the species and life cycle phase.

3. Minerals

Minerals are inorganic elements necessary for the proper functioning of the organism of fishes. Macrominerals (of which higher doses are needed), which are sodium, chlorine, potassium and phosphorus, regulate the maintenance of colloidal systems (osmotic pressure, viscosity and diffusion) and assist in the formation and maintenance of bones. The microminerals are copper, chromium, zinc, selenium and iodine, and are necessary for proper enzyme and hormonal functioning.

Fishes are able to capture minerals from two sources, the environment, through the gills, and feed.

Mineral requirements vary between marine and freshwater fish, because, in the marine environment, the number of ions present in the environment is higher. Therefore, the supply of minerals in feed is more important in freshwater aquaculture species.