The global aquaculture industry primarily revolves around a few key freshwater and marine fish species. This document provides a comprehensive overview of the nutritional requirements of various fish species, focusing on their energy, protein, essential amino acids (EAA), lipids, carbohydrates, vitamins, minerals, and phytogenic compounds. Understanding these requirements is crucial for optimizing aquaculture practices and ensuring the health and growth of fish in both freshwater and marine environments.
Protein Requirements
Carnivorous fish species, such as Atlantic salmon, croaker, seabream, and seabass, have high dietary protein requirements, often nearing 50% depending on their life stage. In contrast, herbivorous species like cyprinids (e.g., common carp, grass carp, and catla) require about 40% protein. The essential amino acid (EAA) profile of the diet is critical for optimal growth, and the crude protein requirements can be lowered if a high-quality protein source with a balanced EAA to non-essential amino acid (NEAA) ratio is provided.
Both freshwater and marine fish require ten essential amino acids: Arginine (Arg), Histidine (His), Isoleucine (Ile), Leucine (Leu), Lysine (Lys), Methionine (Met), Phenylalanine (Phe), Threonine (Thr), Tryptophan (Trp), and Valine (Val). However, the specific amino acid requirements vary with the species’ trophic level. Fish at higher trophic levels typically have lower requirements for Lysine, Threonine, and the combination of Phenylalanine and Tryptophan compared to those at lower trophic levels.
Lipid Requirements
Lipids serve as the primary energy source for fish, with distinct differences between freshwater and marine species. Freshwater fish generally require a lipid content of 3–12% dry matter (DM), while marine species, such as Atlantic salmon, need between 9% and 30% DM. Traditionally, aquafeeds have relied on fish oil, rich in polyunsaturated fatty acids (PUFA), including linoleic acid (LA), α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Recent studies have shown that both marine and freshwater fish can synthesize EPA and DHA endogenously, although the efficiency of this biosynthesis varies by species. Marine fish generally lack the ability to synthesize these fatty acids, while some diadromous species, like Atlantic salmon, can elongate ALA into EPA and DHA.
Energy Requirements
Fish require energy for metabolic processes and growth, which is derived from the metabolic oxidation of proteins, lipids, and carbohydrates in their diet. In growing fish, energy is first used to synthesize structural biomolecules, followed by the production of storage molecules like triglycerides and glycogen. Historically, energy was supplied primarily through fishmeal and fish oil, but the inclusion of plant-based ingredients has introduced alternative energy sources, such as starch, which can reduce protein and lipid requirements. Herbivorous species, like common carp, can tolerate starch inclusion levels of up to 45%, while carnivorous species, such as salmon and seabass, have a lower capacity for starch digestion. Processing methods like cooking and extrusion can enhance starch digestibility.
Vitamin Requirements
Vitamins are essential for various physiological functions in fish, including embryogenesis, skeletal integrity, growth, reproduction, immune response, vision, appetite, and flesh quality. Although vitamin requirements are relatively low, deficiencies can lead to severe health issues, such as skin and fin erosion, organ damage, anemia, and neurological dysfunctions. Many vitamins are naturally present in fishmeal and fish oil, as well as in terrestrial ingredients. Carotenoids, which possess anti-inflammatory properties and antioxidant activity, can complement the functions of vitamins A, E, and C, potentially reducing the need for these vitamins in aquaculture feeds.
Mineral Requirements
The role of minerals, particularly trace elements, in fish health and growth has been less studied. Phosphorus and calcium are crucial for bone development, while the roles of trace elements like zinc, selenium, and manganese are only recently being explored. Phosphorus and calcium sources are commonly included in modern aquafeeds, with known requirements established for species such as common carp, Atlantic salmon, gilthead seabream, large yellow croaker, and European seabass. Zinc is vital for immune function, selenium enhances antioxidant defenses, and magnesium supports immune integrity, all contributing to the overall health of aquaculture fish.
Phytogenic Compounds
Phytogenic molecules, including carotenoids, polyphenols, flavonoids, polysaccharides, and bioactive peptides, have been shown to improve fish’s antioxidative and anti-inflammatory responses. These compounds are abundant in various non-conventional terrestrial ingredients and their inclusion in aquafeeds is increasingly recognized for their positive effects on fish growth performance and immune response.
Carotenoids, which are fat-soluble pigments found in fruits, vegetables, and grains, are classified into xanthophylls (e.g., lutein and zeaxanthin) and carotenes (e.g., α-carotene, β-carotene, and lycopene). Astaxanthin, canthaxanthin, fucoxanthin, and β-carotene play significant roles in disease prevention, inflammation reduction, and overall health maintenance in fish. Additionally, carotenoids contribute to muscle pigmentation, enhancing the visual appeal of aquaculture products. Supplementation with carotenoids is particularly important for salmonids, with specific requirements for astaxanthin and canthaxanthin.
conclusion
Understanding the nutritional requirements of fish is essential for optimizing aquaculture practices and ensuring the health and growth of various species. By addressing the specific needs for proteins, lipids, carbohydrates, vitamins, minerals, and phytogenic compounds, aquaculture can continue to thrive and meet global demands
