7.5 Vitamins

Fish often do not make enough vitamins in their bodies. Vitamins are included in fish rations to ensure adequate growth and health intake. Vitamins are classified as water-soluble or fat-soluble, depending on where the body typically stores them. Water-soluble vitamins are more transient since freshwater fish have a relatively large flow of water traversing the body. Fish have little in the way of reservoirs of water-soluble vitamins. In contrast, fat-soluble vitamins can be stored in fats and other lipids in the body and hence can be held in reserve much longer than water-soluble vitamins.

Water Soluble Vitamins

Fish have almost the same requirements as mammals for water-soluble vitamins. The list of water-soluble vitamins includes B vitamins, inositol, choline, and vitamin C (ascorbic acid). The dietary source is crucial and must be provided daily to avoid deficiency symptoms. Providing reliable water-soluble vitamins can be tricky or difficult because pelleted feed becomes water-logged if not eaten promptly. This water-logging leaches water-soluble vitamins from the pellet.

B-vitamins

B vitamins include thiamine (vitamin B1), riboflavin (vitamin B2), niacin, pantothenic acid, pyridoxine (vitamin B6), biotin, folate, and cobalamin (vitamin B12). B vitamins mainly function as coenzymes or cofactors of intermediate metabolism B vitamin deficiencies result in general symptoms that are not specific enough to lead the clinician to an easy diagnosis. The general maladies of most B vitamins include reduced growth and feed intake (anorexia), anemia (except B-1, thiamine), and discoloration of the body (pantothenic acid, niacin, and vitamin B12 do not affect coloration). The frequent and likely water-soluble vitamin deficiencies in fish culture are thiamine, niacin, pantothenic acid, and pyridine.^[1]

B1: Thiamine

Thiamine is a coenzyme in the enzymes in carbohydrate metabolism. Therefore a deficiency is expected to show signs in energy-consuming organs like the brain, eye lens, and red blood cells. Dietary levels are usually sufficient, with 1.0- 11 mg/kg. However, other dietary components, such as starch in plant ingredient diets, can interfere with availability.^[2] The enzyme that breaks down thiamine, thiaminase, can be very high in some species. Of course, no problem for living fish, but a real problem when feeding raw fish with high thiaminase to other animals. Thiamine decline can also affect aquarium fish-fed live fish, for example. But processed fish meal has had the thiaminase destroyed in the heating of the preparation. Be aware of this possible need to add thiamine to the diet when live or fresh, unprocessed fish (trash fish or feeder fish) are used. Aquarium fish are susceptible when some live fish are fed to the captive fish.

B2: Riboflavin

This vitamin is intimately involved in metabolism as coenzymes in oxidases and reductases for the metabolism of all macronutrients. Catfish fingerlings, in particular, require between 4-6 mg/kg to avoid gross signs of deficiency such as cataracts but as high as 9 mg/kg for maximum growth performance.^[3] Smaller fish have greater requirements than larger and more mature fish.

B3: Niacin

Niacin is called nicotinic acid and is involved in the coenzyme metabolizing carbohydrates, lipids, and proteins. The most commonly reported signs of deficiency occur in the skin and fins when hemorrhage and erosions occur. Suggested recommendations vary greatly from species to species. The recommended levels for best growth range from 7 -150 mg/kg. There is some effect when carbohydrates are added to plant-based diets given to carnivores.^[4]

B5: Pantothenic acid

Pantothenic acid participates in the coenzyme A process of energy metabolism in mitochondria. Tissues with high energy use and frequent cell division will show the first signs of deficiency. Gills of pantothenic acid deficient fish will become clubbed and thickened due to epithelial hyperplasia.^[5] Deficiency is avoided in many species with pantothenic acid levels in the diet from 10 to 45 mg/kg.

B6: Pyridoxine

Vitamin B6 is a group of three chemicals in their phosphate esters. The vitamin is added to fish diets as pyridoxine HCl salt. The Vitamin B6 compounds are involved in numerous reactions to metabolize amino acids and lipids. A few species, i.e., rainbow trout and Snakehead fish (Channidae). Generally, Vitamin B6 deficiency is shown in poor growth and low hematopoiesis. There are reports of nervous system involvement, such as what appeared to be epileptiform fits.^[6] Vitamin B6 dietary requirements vary across species, requiring 1-15 mg/kg of prepared diet.

Biotin

Biotin is involved in many metabolic processes because of enzyme requirements to properly act in the activity. Metabolic pathways such as long-chain fatty acid production require biotin. Biotin deficiency is difficult to produce artificially for research unless the glycoprotein avidin from raw chicken egg white is included. Natural diets are seldom deficient. Manufactured diets include some level of biotin. When deficient levels do occur, there is slowed growth and change in skin coloration.^[7]

Folic acid

Folic acid, after enzymatic reduction, acts as an intermediary in other enzymatic actions leading to amino acid metabolism. Deficiencies in various species have been described as poor growth, anemia, and dark skin.^[8]

B-12 Cobalamin

Animals and plants do not synthesize vitamin B-12 by gastrointestinal microorganisms. Only trace amounts are required, but they are essential in developing red-blood cells’ metabolism of fatty acids. Cobalamin deficiency may be confused with folic acid deficiency. This vitamin may increase appetite in some animals during recovery from disease and surgery.^[9]

Vitamin C

“Fish” vary in their ability to synthesize vitamin C or ascorbic acid. All teleost species should be considered unable to synthesize sufficient ascorbic acid levels.^[10] So-called primitive fish are generally noted to synthesize ascorbic acid. Hagfish, sturgeon, sharks, rays, and lampreys can synthesize ascorbic acid.^[11],^[12],^[13] The enzyme, L-gluconolactone oxidase is required to synthesize the essential nutrient. Those fish that do not have the oxidase enzyme for glucose synthesis will need a sufficient level in their diet.

Vitamin C is very labile to processing conditions and storage time. Vitamin C should be stabilized to assure longer-term nutrient value in the diet. Typically, six months is the expected shelf-life of ascorbic acid in its native form. Several algae may contain vitamin C as a natural source in some fish species.^[14] Therefore, feral predators benefit from eating whole fish with sufficient Vitamin C. Sufficient stabilized Vitamin C in formulated diets needs to be verified in all cases to be safe.

Vitamin C performs the same functions for teleosts provided to other vertebrates. Fish need vitamin C for normal bone and collagen development and replacement. Vitamin C enhances iron absorption in the gut, and anemia may become a problem without sufficient ascorbic acid and lower iron supplementation.

There are few pathognomonic symptoms or signs specific to ascorbic acid deficiency. The signs are mostly structural to the spine, operculum, skin, and eyes. The skeletal deformity in Image 7.02 could be caused by Vitamin C deficiency.^[15] However, there are many other etiologies to consider in spinal deformities of various species.

Fat Soluble Vitamins

Vitamins A, D, E, and K are classical fat-soluble vitamins essential to vertebrates, and teleost fish are no exception. These vitamins are absorbed from the gastrointestinal tract along with dietary fats. One must be aware that conditions favoring fat absorption also affect the absorption of fat-soluble vitamins. These vitamins come from natural feeds or formulated diets. Vitamins are not toxic in mild excess for a short duration. Fat-soluble vitamins are stored in the fat and lipids of the body. However, consistent and long-standing overdosing will lead to disease manifestations. Vitamin deficiency can occur with disease symptoms becoming apparent. The common clinical history of vitamin deficiency is poor growth.

Vitamin A

Vitamin A is essential for regenerating rhodopsin in the retina, which is light-sensitive and involved in vision. Otherwise, Vitamin A is essential in supporting growth, immune function, reproduction, and skin regeneration. Fish can utilize pro-vitamin A compounds such as the carotenoids like B-carotene and xanthin compounds to support the vitamin A requirement. Mammals are more limited in pro-vitamin A sources and utilize carotenoids for other biological purposes. The “other metabolic purposes” have not been well described in fish.^[16]

Vitamin D

Vitamin D is of special note since fish cannot synthesize Vitamin D (with one notable exception currently reported) via the skin since water blocks the entry of UVB of sunlight from penetrating below the surface. Therefore, all Vitamin D must be supplied via the diet. Rainbow trout, however, can produce vitamin D in the skin when exposed to visible blue light. It is also notable that vitamin D activation (from cholecalciferol to calcitriol) in trout occurs in the liver rather than in the kidneys, as in land animals.^[17] Vitamin D has two natural sources: ergocalciferol (Vit D₂) and cholecalciferol (Vit D₃) which are altered in the liver and sent to the kidney to be modified to 1,25-dihydroxyvitamine D₃. The active form of Vitamin D arises in the kidney, not from the diet. The active form of Vit D is involved in the absorption, transport, mobilization, and use of calcium and phosphorus in unison with parathyroid and calcitonin activities. Deficiency presents poor growth and eventually displays changes in the white muscle, especially in the epaxial muscles above the spine. Excess Vitamin D has not been found to cause renal calcinosis as described in Rainbow trout with excess calcium.^[18]

Vitamin E

Vitamin E is several molecules described in comparison to α-tocopherol activities. The highest biopotency is d-α-tocopherol. Vitamin E and selenium work in unison as effective antioxidants to squelch oxidation against cellular phospholipids and proteins. Signs of Vitamin E deficiency have signs of atrophy of white muscle, especially anemia, poor growth, edema of the heart, and depigmentation of the liver. The signs of Vitamin E can be further exaggerated by selenium deficiency, similar to the mammalian Vitamin E/Selenium deficiency syndrome.

Vitamin K

Vitamin K is a group of compounds known best for involvement in blood coagulation and bone density. The stimulation of prothrombin activity and synthesis of Vitamin K-dependent clotting factors is part of Vitamin K’s functions. Vitamin K is necessary for formulated feeds to avoid coagulation problems. In other animals, a source of Vitamin K can originate from gut microbial activity. A gut microbial supply of Vitamin K has not been reported in fish. Vitamin K is a regulator of bone

formation and mineral maturation. Interestingly, Udagawa 2001 & 2004 investigated the vertebral malformation in fish fed Vitamin K deficient diets, and the malformations in offspring of brood fish fed Vitamin K deficient diets.^[19],^[20]