What are the key roles of vitamins in aquaculture
Vitamins are essential for maintaining the health of aquatic animals and promoting their growth and development. Many of these substances cannot be synthesized in the body from other substances, or are synthesized only in very small amounts, and must be supplied through food. If intake is insufficient over the long term, or if requirements cannot be met for other reasons, it will lead to metabolic disorders, stunted growth and reduced resistance to disease in fish and shrimp.
Classification of vitamins
According to their solubility, vitamins can be divided into two major categories: fat-soluble vitamins and water-soluble vitamins.
1. Fat-soluble vitamins: vitamin A, D, E, K, etc.
2. Water-soluble vitamins: vitamin B1, B2, B3, B5, B6, biotin (vitamin H, vitamin B7), folic acid, vitamin B12 and vitamin C, etc.
Fat-soluble vitamins
1. Vitamin A: Vitamin A is an unsaturated alcohol with a β-ionone ring, and in animals vitamin A usually exists as an ester formed with fatty acids. Vitamin A is chemically active and easily destroyed by oxidation and ultraviolet light. The main functions of vitamin A are:
①. Promoting the synthesis of mucopolysaccharides, maintaining the integrity and normal permeability of cell membranes and epithelial tissues.
②. Participating in the formation of the photosensitive substance in visual cells (rhodopsin), and playing an important role in maintaining the photosensitivity of the retina.
2. Vitamin D: Vitamin D is a general term for a class of anti-rachitic substances, chemically belonging to steroid derivatives, of which the two most common are D2 and D3. D2 is also known as ergocalciferol, and D3 as cholecalciferol; their molecular structures are very similar, differing only in the side chain. Vitamin D is a colorless crystal with stable chemical properties, and is not easily destroyed by acids, alkalis, oxidizing agents or heating. The physiological function of vitamin D: mainly promoting bone formation.
3. Vitamin E: Vitamin E is also known as tocopherol. It is stable to heat and acids, relatively unstable to alkalis, and easily oxidized. When it is present together with substances that are easily oxidized, such as vitamin A or unsaturated fatty acids, it can protect vitamin A and unsaturated fatty acids from oxidation. Therefore vitamin E can serve as an antioxidant for these substances. The esters of vitamin E are relatively stable and are commonly used as feed additives. The physiological functions of vitamin E: anti-infertility function; as an antioxidant, it protects the unsaturated fatty acids on cell membranes from oxidation, thereby maintaining the integrity and normal function of cell membranes; it protects red blood cell membranes, increasing their resistance to hemolytic substances, and at the same time protects sulfhydryl groups from oxidation, thereby protecting the activity of many enzymes. In addition, vitamin E also participates in regulating tissue respiration and oxidative phosphorylation, and promotes the production of thyroid-stimulating hormone (TH), adrenocorticotropic hormone (ACTH) and gonadotropins.
4. Vitamin K: Vitamin K is a class of quinone compounds. It is relatively stable and heat-resistant, but can be destroyed by alkalis and light. The physiological functions of vitamin K: participating in blood coagulation, and promoting the synthesis of prothrombin and clotting factors in the liver.
Water-soluble vitamins
1. Vitamin B1: Also known as thiamine, it is a white powder, and its hydrochloride is a needle-shaped crystalline substance that is extremely soluble in water. B1 is relatively stable in acidic solution, but is easily destroyed by oxidation in alkaline and neutral solutions. It is found in relatively large amounts in yeast, cereal germ and bran layers, lean meat, nuts and eggs. The physiological functions of vitamin B1: as a coenzyme of pyruvate oxidative decarboxylase, α-ketoglutarate oxidative decarboxylase and transketolase, it plays an important role in maintaining normal carbohydrate metabolism in the body. In addition, B1 also participates in the valine synthesis process in bacteria, yeast and plants.
2. Vitamin B2: Also known as riboflavin (so named chemically because its structure contains ribose and isoalloxazine and it is yellow in color). B2 is slightly soluble in water and alcohol, but insoluble in other organic solvents; it is relatively stable in acidic solution, but readily decomposes in alkaline solution or when exposed to visible light. B2 is widely distributed in animals and plants, and is present in high amounts in rice bran, yeast, liver, milk and beans. The physiological functions of vitamin B2: in the body it exists in the forms of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). FMN and FAD are coenzymes of many oxidoreductases in the body, and play a role in transferring hydrogen in redox reactions. In addition, B2 plays an important role in maintaining the normal functions of skin, mucous membranes and vision.
3. Vitamin B3: Also known as pantothenic acid, it is a dipeptide derivative and is soluble in water and ether. B3 is relatively stable to oxidizing agents and reducing agents, and is also very stable when heated in the presence of water. However, it is easily destroyed when heated dry or in acidic or alkaline media. It is widely present in animals and plants, and is especially abundant in bran, rice bran and oilcake-type feeds. The physiological functions of vitamin B3: in the body it is the raw material for synthesizing coenzyme A, and coenzyme A is a coenzyme related to acylation, playing a very important role in transferring acetyl groups during the metabolism of carbohydrates, fats and proteins.
4. Vitamin B5 (nicotinic acid and nicotinamide): formerly called vitamin PP or anti-pellagra vitamin, it includes two compounds, nicotinic acid (niacin) and nicotinamide (niacinamide). Both are white needle-shaped crystals and are relatively stable to heat, light and acids. Nicotinic acid is slightly soluble in water, but can dissolve in large amounts in alkaline solution; nicotinamide is easily soluble in water and ethanol, and when heated in alkaline solution, nicotinamide can be hydrolyzed to nicotinic acid. Nicotinic acid and nicotinamide are very widely distributed, and are found in relatively large amounts in yeast, lean meat, liver, peanuts, soybeans, and cereal bran layers and germ. The physiological functions of vitamin B5: nicotinic acid becomes active only after being converted into nicotinamide in the body; nicotinamide is a component of coenzyme I (NAD) and coenzyme II (NADP), and plays an important role in redox reactions in the body.
5. Vitamin B6: That is, pyridoxine. It has three chemical forms, namely pyridoxol, pyridoxal and pyridoxamine. In the body, pyridoxol can be converted into pyridoxamine and pyridoxal, but the latter two cannot be converted into pyridoxol, while pyridoxal and pyridoxamine can interconvert. Because pyridoxal and pyridoxamine are very unstable and are rapidly destroyed by heat, light and air, B6 is generally supplemented in the form of pyridoxine hydrochloride. Pyridoxine hydrochloride is easily soluble in water and resistant to high heat in acidic and alkaline solutions, but is easily destroyed when exposed to visible light. Vitamin B6 is widely distributed in nature, and is found in relatively large amounts in grains, legumes, seed coats and grasses. The physiological functions of vitamin B6: it is closely related to amino acid metabolism.
6. Biotin (vitamin H, vitamin B7): Biotin is relatively stable chemically and is not easily destroyed by acids, alkalis or light, but high temperature and oxidizing agents can make it lose its activity. The physiological functions of biotin (vitamin H, vitamin B7): it is a coenzyme of many carboxylases in the body, participates in carboxylation reactions in material metabolism, such as the carboxylation of pyruvate to oxaloacetate, and plays an important role in the reaction of fatty acid synthesis in the body.
7. Folic acid: Folic acid is also known as the anti-anemia factor. It is a yellow crystalline substance, slightly soluble in water, stable in acidic solution, but easily decomposes when heated or exposed to light. The physiological functions of folic acid: in the body, it is catalytically hydrogenated by folate reductase to become tetrahydrofolic acid (THFA). THFA is a coenzyme of one-carbon group (such as -CH3, -CH2OH, -CH2-) transferases in the organism, and the transfer of one-carbon groups is very closely related to the synthesis of purines and pyrimidines and to amino acid metabolism.
8. Vitamin B12: Also known as cyanocobalamin, it is a pink crystal, very stable in weakly acidic solution, but easily decomposes below pH3 or above pH9. B12 can be destroyed by the presence of oxidizing agents and reducing agents. Animal liver and muscle contain relatively large amounts of vitamin B12, but plants do not contain B12. Many microorganisms (such as certain microorganisms in the digestive tract of animals) can synthesize B12. The absorption of B12 depends on the presence of an intrinsic factor in the intestine (a mucoprotein secreted by the intestinal wall). The physiological functions of vitamin B12: it participates in the metabolism of one-carbon groups in the body and is a coenzyme for transferring methyl groups, and its action is linked with that of folic acid.
9. Vitamin C: Also known as ascorbic acid, it is a six-carbon polyhydroxy lactone with acidity and strong reducing properties. It is easily soluble in water and very stable when heated in acidic solution, but is quickly destroyed in alkaline solution. Because of its strong reducing properties, it is extremely easily destroyed by oxidizing agents. Vitamin C is present in relatively high amounts in green feed. The physiological functions of vitamin C:
①. An essential substance for synthesizing intercellular substances such as collagen and mucopolysaccharides;
②. It can convert oxidized glutathione in the body into reduced glutathione, thereby protecting the active SH groups of enzymes and relieving the toxicity of heavy metals;
③. As a reducing agent, it participates in redox reactions in the body;
④. It participates in other metabolic reactions in the body, such as the conversion of folic acid to tetrahydrofolic acid, tyrosine metabolism and the synthesis of adrenal cortical hormones, all of which require vitamin C;
⑤. The intestinal absorption of iron also requires vitamin C.
10. Choline: Choline is a constituent of lecithin and participates in the formation of lipoproteins, which helps fats to be transported out of the liver, and therefore has the effect of preventing fatty liver. Choline has three unstable methyl groups and plays the role of a methyl donor in transmethylation reactions. The physiological functions of choline: the choline derivative acetylcholine is very important in the transmission of nerve impulses.
11. Inositol: Inositol is a cyclohexane derivative, similar to choline, with obvious lipophilic properties. The physiological functions of inositol: it participates in the metabolism of certain lipids and prevents fat deposition in the liver.
12. Vitamin K: A class of quinone compounds. It is relatively stable and heat-resistant, but can be destroyed by alkalis and light. The physiological functions of vitamin K: participating in blood coagulation, and promoting the synthesis of prothrombin and clotting factors in the liver.