Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 147
Vitamins
ОглавлениеVitamins serve as cofactors, hormones, and regulators of cellular differentiation. They are generally required from the diet in trace amounts. Vitamins may be categorized as fat‐soluble (vitamins A, D, E, K) or water‐soluble (B vitamins including thiamine [B1], riboflavin [B2], niacin [B3], pantothenate [B5], pyridoxine [B6], biotin [B7], folate [B9], cobalamin [B12]; vitamin C [ascorbic acid]; choline). Requirements are affected by size, age, growth rates, environmental factors, and inter‐relationships with other nutrients (NRC 2011). Larval fish nutrition presents some unique concerns related to vitamin nutrition and is discussed in more detail later. Estimated vitamin requirements are presented in Table A4.3. As with other nutrients, these recommended levels are generally determined for optimal performance of aquaculture species and so should be used as a guideline rather than an instruction.
Fat‐soluble vitamins A, D, E, and K may be supplemented in diets, but present a higher risk of toxicity since they are stored in liver and adipose and are harder to excrete in excess.
Vitamin A is involved in cellular differentiation and vision. Deficiency in larval fish is associated with incomplete eye migration, abnormal pigmentation, and skeletal abnormalities, while in juvenile fish, skin and liver hemorrhages, exophthalmos, and twisted gill opercula have been described (NRC 2011; Hamre et al. 2013). Carotenoids are pro‐vitamin A compounds (and pigments) that occur naturally in many wild‐type food items. Carotenoids are generally considered less toxic since the conversion of carotenoid to retinol is regulated in response to body vitamin A levels. In several freshwater and saltwater fish species, β‐carotene, astaxanthin, and canthaxanthin can be converted to vitamin A, although their conversion seems most efficient when vitamin A levels are low (Moren et al. 2002). The use of astaxanthin and canthaxanthin as precursors to vitamin A is somewhat unique – most birds and mammals studied are not able to convert these carotenoids to vitamin A (Goodwin 1986).
Table A4.2 Total lipid and fatty acid composition of seafood items commonly fed to fish.
Source: Gruger et al. (1964). © John Wiley & Sons.
| Pacific herring, fillet (Clupea pallasii) | Atlantic mackerel, fillet (Scomber scombrus) | Menhaden, whole (Brevoortia tyrannus) | Coho salmon, fillet (Oncorhyncus kisutch) | Lake herring (Coregonus artedii) | Rainbow trout (Oncorhyncus mykiss) | Lake whitefish (Coregonus clupeaformis) | Blue crab (Callinectes sapidus) | Littleneck clam (Protothaca staminea) | Pacific oyster (Crassostrea gigas) | |
|---|---|---|---|---|---|---|---|---|---|---|
| Tissue lipid content (%) | 12.8 | 3.2 | 15 | 7.5 | 2.5 | 2.5 | 2.2 | 2.1 | 0.5 | 2.5 |
| Lipid fatty acid composition (%) | ||||||||||
| 16:0 palmitic acid | 15.1 | 28.2 | 28.9 | 10.2 | 17.7 | 8.2 | 10.5 | 15.2 | 23.8 | 21.4 |
| 18:1n9 oleic acid | 16.9 | 19.3 | 19.3 | 18.6 | 18.1 | 19.8 | 27.2 | 17.6 | 10.8 | 8.5 |
| 18:2n6 linoleic acid | 1.6 | 1.1 | 1.1 | 1.2 | 4.3 | 4.6 | 5.5 | 1.9 | 1.4 | 1.2 |
| 18:3n3 linolenic acid | 0.6 | 1.3 | 1.3 | 0.6 | 3.4 | 5.2 | 3.7 | 1.2 | 1.6 | 1.6 |
| 20:5n3 EPA | 8.6 | 8.6 | 7.1 | 12 | 5.9 | 5 | 6.4 | 13.4 | 10 | 21.5 |
| 22:6n3 DHA | 7.6 | 7.6 | 10.8 | 13.8 | 13.3 | 19 | 8.8 | 11 | 14.5 | 20.2 |
| Calculated fish fatty acid content (%) a | ||||||||||
| 16:0 palmitic acid | 1.9 | 0.9 | 4.3 | 0.8 | 0.4 | 0.2 | 0.2 | 0.3 | 0.1 | 0.5 |
| 18:1n9 oleic acid | 2.2 | 0.6 | 2.9 | 1.4 | 0.5 | 0.5 | 0.6 | 0.4 | 0.1 | 0.2 |
| 18:2n6 linoleic acid | 0.2 | 0.0 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 |
| 18:3n3 linolenic acid | 0.1 | 0.0 | 0.2 | 0.0 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 |
| 20:5n3 EPA | 1.1 | 0.3 | 1.1 | 0.9 | 0.1 | 0.1 | 0.1 | 0.3 | 0.1 | 0.5 |
| 22:6n3 DHA | 1.0 | 0.2 | 1.6 | 1.0 | 0.3 | 0.5 | 0.2 | 0.2 | 0.1 | 0.5 |
All values are on an as‐fed basis.
EPA: eicosapentaenoic acid; DHA: docosahexaenoic acid.
a Calculated fish fatty acid content represents the proportion of the fatty acids relative to total fat content.
Table A4.3 Dietary vitamin requirements for teleosts and elasmobranchs.
Sources: Janse et al. (2004), Fernández‐Palacios et al. (2011), NRC (2011), and Hamre et al. (2013). © John Wiley & Sons.
| Juvenile teleost | Larval teleost | Broodstock teleost | Elasmobranchs | |
|---|---|---|---|---|
| Ascorbic acid (ppm) | 28 (15–54) | (25–2500) | (25–50) | (100–1100) |
| Biotin (ppm) | 0.58 (0.06–1) | (0.1–1.5) | ||
| Choline (ppm) | 811 (400–1500) | (600–3000) | ||
| Folate (ppm) | 1.3 (1.0–2.0) | (5–10) | ||
| Niacin (ppm) | 40 (10–150) | (20–200) | ||
| Pantothenate (ppm) | 23 (10–36) | (12–50) | ||
| Pyridoxine (ppm) | 7 (3–15) | Required | (3–20) | |
| Riboflavin (ppm) | 7 (4–11) | (4–20) | ||
| Thiamine (ppm) | 5 (1–11) | (1–10) | ||
| Vitamin B12 (μg/kg) | 35 (20–50) | (10–20) | ||
| Vitamin A (IU/kg)a | 5854 (1667–18 667) | (16 665–103 323) | (1000–4000) | (2000–2500) |
| Vitamin D (IU/kg)a | 820 (360–1600) | 19 000 | (500–2400) | 2400 |
| Vitamin E (IU/kg)a | 60 | (50–190) | (30–50) | |
| Vitamin K (mg/kg) | <10 | (5–10) |
All values are on a dry matter basis and represent the mean (range) from published literature.
a Vitamin conversions: vitamin A: 1 mg retinol = 3333 IU; 1 mg retinyl acetate = 2906 IU; 1 mg retinyl palmitate = 1818 IU; vitamin D: 1 μg cholecalciferol = 40 IU; vitamin E: 1 mg D‐α‐tocopherol = 1.49 IU; 1 mg D,L‐α‐tocopherol = 1.1 IU; 1 mg D‐α‐tocopheryl acetate = 1.36 IU; 1 mg D,L‐α‐tocopherol acetate = 1 IU.
Vitamin D functions in calcium homeostasis and is important for the development of skeletal tissues and cellular differentiation (NRC 2011). Vitamin D can be sourced from plants (ergocalciferol or vitamin D2) and animals (cholecalciferol or vitamin D3). Of these, D3 is significantly more effective than D2. Larval requirements for vitamin D seem to be significantly higher than those of juvenile fish. Toxicity can result in vertebral deformities, so further research is warranted before recommendations of high intakes for larval fish are made (Hamre et al. 2013).
Within the family of vitamin E molecules, α‐tocopherol is the most biologically active form of the tocopherols and tocotrienols. These serve as antioxidants, stabilize membranes, affect eicosanoid signaling and cellular proliferation, and modulate immune responses. Efficacy of vitamin E as an antioxidant is dependent on levels of other antioxidants such as vitamin C and selenium‐based glutathione systems. When the latter are low, vitamin E can become a pro‐oxidant (Hamre 2011). As an antioxidant, vitamin E protects PUFAs at an approximate ratio of 1 molecule vitamin E:1000 molecules PUFA, with higher levels of unsaturation requiring more protection (Schwarz et al. 1988; Hamre 2011). This is why nutrient requirements for vitamin E are often described in relation to the PUFA content of the diet. This is particularly critical for fish, where diets are often rich in PUFA. Vitamin E requirements in most experiments are determined based on maximal growth rates. When other parameters are used (e.g. red blood cell fragility, immune responses), higher requirements are predicted. For example, Malabar grouper (Epinephelus malabaricus) required 60–100 mg D,L‐α‐tocopheryl acetate/kg diet for growth and up to 800 mg/kg for better nonspecific immune parameters (Lin and Shiau 2005). Requirements may increase further during disease (Durve and Lovell 1982). Commercially prepared larval fish feeds may require higher vitamin E due to the large surface area, higher risk of lipid oxidation, and high level of omega‐3 PUFAs, particularly for marine fish (Hamre 2011). Very high levels of dietary vitamin E (5000–10 000 IU/kg) have been shown to promote oxidation and damage erythrocytes (NRC 2011).
Little work has been conducted on vitamin K in fish. Existing research has been inconsistent in showing a dietary requirement or GI microbial synthesis of vitamin K in fish (NRC 2011).
Water‐soluble vitamins pose a lower risk of toxicity and are frequently supplemented at high levels to ensure optimal levels are met. Research has focused primarily on defining minimal requirements. Of the water‐soluble vitamins, vitamin C receives the most attention. It is considered an essential or semi‐essential dietary nutrient for teleosts, as there is evidence that some cartilaginous fish can synthesize ascorbic acid de novo (Cho et al. 2007). However, it is unclear if de novo synthesis is adequate to meet needs in all life stages and environmental conditions, and it has been demonstrated that supplemental vitamin C improves immune responses in some species with de novo synthesis (Xie et al. 2006). So it is advisable to supplement vitamin C in the diet of all fish species. Signs of vitamin C deficiency include lordosis, scoliosis, cartilage and collagen defects, petechial hemorrhaging, and fractures of the spine (Halver et al. 1975; Sandnes et al. 1992). These have been reported within weeks of feeding a vitamin C‐deficient diet (Halver et al. 1975; Sandnes et al. 1992). Minimum requirements for growth are often much lower than the requirements for optimal immune function (Ai et al. 2004). While minimum requirements for fish are ~50 mg/kg diet, much higher doses (190–1000 mg/kg diet) often result in significant improvements in immune function, notably antibody production, complement activity, and survival after disease challenge (Navarre and Halver 1989; NRC 2011; Hamre et al. 2016). Vitamin C needs are increased during reproduction and larval fish growth (NRC 2011). Since vitamin C is heat labile, stabilized forms should be used for supplementation, e.g. L‐ascorbyl‐2‐polyphosphate. The requirement for vitamin C is related to the level of vitamin E in the diet, as vitamin C or vitamin E can counteract the signs of deficiency of the other nutrient to some extent (Wahli et al. 1998; Sealey and Gatlin 2002).
Work on B vitamins in fish is limited. Thiamine (B1) is of concern for any fish‐eating species, as thiaminases in fish tissues are activated upon death and rapidly destroy available thiamine. Thiaminase activity is particularly high in clupeids such as alewives (Alosa pseudoharengus) and capelin (Mallotus villosus), and cyprinids such as feeder goldfish (Carassius auratus). Any frozen/thawed fish should be supplemented with thiamine (Fitzsimons et al. 2005). Thiaminase activity has also been demonstrated in insects, blue‐green algae (Microcystis aeruginosa) and bacteria (Honeyfield et al. 2002). Pyridoxine (B6) may be needed in the diet during larval development, as levels in the yolk sac are depleted rapidly (Hamre et al. 2013; Saha et al. 2016).
Choline, a vitamin‐like nutrient, is an important component of phospholipids and a precursor of the neurotransmitter acetylcholine. Most fish cannot synthesize sufficient choline and it is a common supplement in cultured fish diets, usually as choline chloride (Wilson and Poe 1988). Additionally, choline may reduce excessive lipid accumulation and the development of fatty liver, although studies have produced mixed results (Halver 2002). Some species have shown a negative correlation between dietary choline and liver lipid levels (channel catfish Ictalurus punctatus, hybrid striped bass Morone saxatilis x M. chrysops, barred knifejaw Oplegnathus fasciatus), while others have shown a positive correlation (hybrid tilapia) or no correlation (rainbow trout, yellow perch Perca flavescens, Siberian sturgeon Acipenser baerii) (Wilson and Poe 1988; Rumsey 1991; Griffin et al. 1994; Shiau and Lo 2000; Twibell and Brown 2000; Yazdani‐Sadati et al. 2014; Khosravi et al. 2015). Further studies are needed to understand the potential benefits of supplementing dietary choline.
