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Feature: Selenium in Fish Nutrition

Selenium in fish diets

Selenium is an integral part of the enzyme glutathione peroxidase (GSH-Px) which protects cell membranes and tissues against oxidative damage. The inclusion of Se in the diet of cultured terrestrial animals has generated much interest as it has been found to have benefits for production, reproduction and product quality. In fish, Se is required for normal growth, development and flesh quality. Selenium plays an important role in the maintenance of fish health, in particular fish immunity. Symptoms of Se deficiency in fish include low glutathione peroxidase activity, reduced growth, impaired reproduction, anaemia, exudative diathesis, muscular dystrophy and increased mortality. However, excessive Se can also cause a variety of toxic effects at the biochemical, cellular, organ and system levels. Vitamin E and Se function synergistically in animal tissues to form an important antioxidant defence system. 

A brief overview is given of some of the benefits of selenium supplementation and the effects of excessive and inadequate amounts of Se in fish.

Se requirement
Selenium requirements of fish vary with the form of Se ingested, polyunsaturated fatty acid and vitamin E content of the diet, and the concentration of Se in the water. Interactions between Se and vitamin E have been reported in channel catfish (Gatlin et al., 1986; Wise et al., 1993), Atlantic salmon (Poston et al., 1976), rainbow trout (Bell et al., 1985) and chinook salmon (Thorarinsson et al.,1994). 
GSH-Px activity in the plasma and liver is used as an index of Se status in fish (NRC, 1993). In rainbow trout Se requirement was determined on the basis of optimum growth and maximum plasma GSH-Px activity which occurred at 0.38 mg/kg diet (Hilton et al., 1980); in catfish this occurred at 0.25 mg/kg diet (Gatlin and Wilson, 1984). Lovell (1998) recommended inclusion rates of 0.03, 0.10 and 0.30 mg Se/kg diet in salmonid, catfish and hybrid striped bass diets, respectively. Lin and Shiau (2005) estimated the Se requirement of juvenile grouper, Epinephelus malabaricus to be about 0.7 mg/kg diet. 
Dietary Se levels used in some studies are markedly higher than the ones just discussed. While intracellular superoxide anion production was higher in channel catfish fed on four times (0.8 mg/kg) the recommended level of Se (Wise et al., 1993), Se (1 or 2 mg/kg) supplementation did not appear to benefit performance in Atlantic salmon (Lorentzen et al., 1994). In an earlier study by Julshamn et al. (1990), supplementation at Se 0.66 or 2.6 mg/kg also did not affect growth or feed conversion efficiency in Atlantic salmon. 

Se deficiency
Although increased mortality and compromised immunity are indicative of Se deficiency in fish, there appears to be a significant interaction between Se and vitamin E in fish. Rainbow trout fed on diets without added Se or α-tocopherol for 10 weeks showed reduced appetite, pale swollen gills, brownish-yellow livers and anaemia; those given Se or alpha-tocopherol developed normally (Oberbach and Hartfiel, 1987). Gatlin et al. (1986) observed that while combined deficiencies of Se and vitamin E suppressed growth and caused anaemia, severe myopathy, exudative diathesis and death in fingerling channel catfish, singular deficiencies of either Se or vitamin E did not produce any of these pathological symptoms. Similarly, while Se deficiency reduces growth in rainbow trout (Hilton et al., 1990) and catfish (Gatlin and Wilson, 1984), Se deficiency alone does not produce pathological signs. Both Se and vitamin E are necessary to prevent muscular dystrophy in Atlantic salmon (Poston et al., 1976) and exudative diathesis in rainbow trout (Bell et al., 1985). Atlantic salmon parr given Se-deficient diets (0.017 mg/kg) showed increased levels of indices of tissue peroxidation (Bell et al., 1987). 

Se toxicity
Although Se is an essential element in animal nutrition, toxicity can arise at concentrations only slightly greater than those required. The toxicity of Se is thought to arise from its ability to substitute for sulphur during protein synthesis. This substitution disrupts normal chemical linkages leading to improperly formed proteins and enzymes affecting subcellular, cellular, organ and system functions. Recent studies have also shown that some forms of Se are able to generate oxidative stress in an in vitro test system containing glutathione (Palace et al., 2004). In rainbow trout, chronic dietary Se toxicity occurred at Se 13 mg/kg dry feed, expressed as reduced growth rate, poor feed conversion efficiency and high mortality (Hilton et al., 1980). In channel catfish toxicity was observed at 15 mg/kg diet (Gatlin and Wilson, 1984), with reduced growth and feed conversion efficiency. Hicks et al. (1984) reported that rainbow trout fed on 11.4 mg/kg Se showed reduced weight, feed conversion efficiency and increased mortality; 90% of the fish also developed nephrocalcinosis. Hilton and Hodson (1983) observed renal calcinosis and a decrease in growth and feed conversion efficiency in rainbow trout reared on high-Se and high-carbohydrate diets (10 mg/kg). Mortality increased in chinook salmon exposed for 90 days to ≥ 9.6 mg/kg Se from 2 organic sources (high Se fish meal and SeMet) (Hamilton et al., 1990). Growth was reduced when chinook salmon were fed on ≥ 5.3 mg/kg Se and 18.2 mg/kg Se, from fish meal and SeMet, respectively. 
Fathead minnow (Pimephales promelas) fed on diets containing a mixture of inorganic and organic Se (0.5 to 160 mg/kg diet), had growth significantly inhibited at 20 and 30 mg/kg; no significant treatment effects on any of the reproductive parameters measured were observed (Ogle and Knight, 1989). Teh et al. (2004) showed that chronic exposure to 6.6 mg/kg diet of Se induced deleterious health effects which could potentially impact survival of juvenile splittail (Pogonichthys macrolepidotus). A recent study by Tashjian et al. (2006) showed that the white sturgeon (Acipenser transmontanus) is relatively less sensitive to Se toxicity than other fish species, the threshold dietary Se toxicity concentration being 10 mg/kg diet in an 8-week exposure trial. 

Se and immunity
In a study by Thorarinsson et al. (1994), groups of juvenile spring chinook salmon naturally infected with Renibacterium salmoninarum were given 2 levels of vitamin E (53 or 299 mg/kg diet) and Se (0.038 or 2.49 mg/kg diet in the form of sodium selenite) ; no mortality was observed in those those on the high vitamin E + high Se diet. Mortality was 3% in the group given the low Se + high vitamin E or high Se + low vitamin E diets, and 31% in the group given the low Se + low vitamin E diet. GSH-Px activity in the plasma was also higher in high Se-fed fish. 
In channel catfish subjected to Edwardsiella ictaluri challenge, antibody production increased as dietary Se concentration increased, with maximum survival observed at the highest concentration used (Lovell and Wang, 1997). This indicates that dietary Se is essential for optimal immune response and resistance in channel catfish infected with E. ictaluri. More recently, Lin and Shiau (2007) noted that oxidative stress induced by high copper ingestion in the grouper, E. malabaricus, depressed its immune response. Supplementation of high dietary Se (2 times adequate) was found to reduce the oxidative stress and improve the immune response.

Se and fish quality
Organic Se supplementation is reported to improve salmon flesh texture and coloration, by decreasing astaxanthin oxidation during fish storage and display. In fact a combination of organic Se with increased vitamin E supplementation could confer pigment stability during salmon storage. Thomas & Buchanan (2006) observed that southern bluefin tuna fed diets fortified with vitamins C and E and Se had raised levels of these antioxidants in the muscle. High levels of these antioxidants resulted in an extension of the colour shelf life of sashimi grade tuna meat. Lyons (1998) found that flesh colour, texture and pigment deposition improved in Atlantic salmon given Se-yeast when compared with controls given only fish meal as the sole source of Se. 

Other effects of Se
Bjerregaard et al. (1999) observed that rainbow trout fed a selenite-supplemented (Se 10 μg/g) diet augmented the elimination of organic mercury from muscles, liver, kidney, bile and erythrocytes, but not from blood plasma, compared with trout fed a non-supplemented diet (Se 1.5 μg/g). Dietary Se also augmented the elimination of inorganic Hg in muscles and kidney, but not in the liver, erythrocytes, blood plasma and bile. Although Se 10 μg/g increased liver Se from 1 to 26 mg/kg, neither muscle Se nor growth rate was affected.

Dietary Se sources
Sodium selenite and sodium selenate are the two primary sources of Se while organic sources include Se in fishmeal and that in Se-yeast. The availability of Se from dietary sources varies; as observed in other animal species, organic Se sources in fish diets appear to have higher bioavailability than inorganic Se sources. Bell and Cowey (1989) observed that in a digestibility trial with Atlantic salmon, Se availability was highest from selenomethionine (91.6%), followed by sodium selenite (63.9%) and Se in fishmeal (46.6%). Similarly in studies with channel catfish, selenomethionine was more available than sodium selenite (Lovell and Wang, 1997; Wang and Lovell, 1997). These authors also noted that the Se allowance in the diet of channel catfish can be reduced when selenomethionine or selenoyeast is used instead of inorganic Se.
In a comparison of the net absorption of trace minerals, including Se, from chelated and inorganic sources, Paripatananont and Lovell (1997) found that net absorption of all minerals was higher from the chelated than the inorganic forms in basal diets of channel catfish. Jovanic et al. (1997) found that organically-bound Se (selenium yeast) acts more efficiently on the antioxidant system of carp fingerlings than inorganic Se salts. 
Channel catfish challenged with E. ictaluri were more responsive to organic Se sources when compared to inorganic sources; antibody titre was highest in catfish fed selenoyeast, intermediate for fish fed on selenomethionine and lowest for those fed on sodium selenite (Lovell and Wang, 1997; Wang et al., 1997). Therefore, selenomethionine is more efficacious than the inorganic source of Se in protecting channel catfish from E. ictaluri infection. 

Concluding remarks
While Se supplementation in some species of fish has demonstrated beneficial effects on feed conversion, immune response and growth, studies on other species of fish were unable to demonstrate any such benefits with the introduction of both Se and vitamin E. Salte et al. (1988) reported that the addition of vitamin E (50 mg/kg body weight) or selenium (0.12 mg/kg body weight), or both vitamin E and selenium to the feed of salmon with subclinical Hitra (coldwater vibrosis caused by Vibrio salmonicida) disease, had no significant effect on mean survival rates. No synergistic effects were observed with excessive dietary ascorbic acid, α-tocopheryl acetate and Se supplementation on growth performance and disease resistance to E. tarda in fingerling Nile tilapia (Kim et al., 2003). 
Nevertheless, current available research does indicate that supplementation of Se in cultured fish diets has benefits. The US Food and Drug Administration has approved the use of supplemental Se at 0.1 mg/kg for aquaculture species. Varying levels of Se have been proposed over the years for linking Se concentrations in the whole body or in the diet with adverse effects in fish. DeForest et al. (1999) proposed different thresholds for coldwater (11 mg/kg diet) and warmwater (10 mg/kg diet) fish. According to Hamilton (2003) who carried out a review of studies on Se toxicity and requirements in fish, much of the literature supports a whole-body threshold of 4 mg/kg in fish and 3 mg/kg in the diet.
The fact that fish is a good source of Se in the human diet presents an opportunity for fish farmers to produce Se-enriched fish for improved human health. Future research should focus on elucidating the Se requirements of other cultured species. 

Bell JG, Cowey CB, 1989. Digestibility and bioavailability of dietary selenium from fish meal, selenite selenomethionine and selenocysteine in Atlantic salmon (Salmo salar). Aquaculture 81:61-69.
Bell JG, Cowey CB, Adron JW, Shanks AM, 1985. Some effects of vitamin E and selenium deprivation on tissue enzyme levels and indices of tissue peroxidation in rainbow trout (Salmo gairdneri). British Journal of Nutrition 53:149-157.
Bell JG, Cowey CB, Adron JW, Pirie BJS, 1987. Some effects of selenium deficiency on enzyme activities and indices of tissue peroxidation in Atlantic salmon parr (Salmo salar). Aquaculture 65:43-54.
Bjerregaard P, Andersen BW, Rankin JC, 1999. Retention of methyl mercury and inorganic mercury in rainbow trout Oncorhynchus mykiss (W): effect of dietary selenium. Aquatic Toxicology 45:171-180
DeForest DK, Brix KV, Adams WJ, 1999. Critical review of proposed residue-based selenium toxicity thresholds for freshwater fish. Human Ecological Risk Assessment 5: 1187-1228.
Gatlin DW III, Wilson RP, 1984. Dietary selenium requirement of fingerling channel catfish. Journal of Nutrition 114:627-633.
Gatlin DM III, Poe WE, Wilson RP, 1986. Effects of singular and combined deficiencies of selenium and vitamin E on fingerling channel catfish (Ictalurus punctatus). Journal of Nutrition 116:1061-1067.
Hamilton SJ, 2003. Review of residue-based selenium toxicity thresholds for freshwater fish. Ecotoxicology and Environmental Safety, Environmental Research, Section B 56:201-210.
Hamilton SJ, Buhl KJ, Faerber NL, Wiedemeyer RH, Bullard FA, 1990. Toxicity of organic selenium in diet to chinook salmon. Environmental and Toxicological Chemistry 9:347-358.
Hicks BD, Hilton JW, Ferguson HW, 1984. Influence of dietary selenium on the occurrence of nephrocalcinosis in the rainbow trout, Salmo gairdneri Richardson. Journal of Fish Diseases 7: 379-389.
Hilton JW, Hodson PV, 1983. Effect of increased dietary carbohydrate on selenium metabolism and toxicity in rainbow trout (Salmo gairdneri). Journal of Nutrition 113:1241-1248.
Hilton JW, Hodson PV, Slinger SJ, 1980. The requirement and toxicity of selenium in rainbow trout (Salmo gairdneri). Journal of Nutrition 110: 2527-2535.
Jovanovic A, Grubor-Lajsic G, Djukic N, Gardinovacki G, Matic A, Spasic M, 1997. The effect of selenium on antioxidant system in erythrocytes and liver of the carp (Cyprinus carpio L.). Critical Reviews in Food Science and Nutrition 37: 443-448.
Julshamn K, Sandnes K, Lie O, Waagbo R, 1990. Effects of dietary supplementation on growth, blood chemistry and trace element levels in serum and liver of adult Atlantic salmon (Salmo salar). Fiskeridirektoratets Skrifter Serie Ernaering 3:47-58.
Kim KW, Wang XJ, Choi SM, Park GJ, Koo JW, Bai SC, 2003. No synergistic effects by the dietary supplementation of ascorbic acid, α-tocopheryl acetate and selenium on the growth performance and challenge test of Edwardsiella tarda in fingerling Nile tilapia, Oreochromis niloticus L. Aquaculture Research 34:1053-1058.
Lin YH, Shiau SY, 2005. Dietary selenium requirements of juvenile grouper, Epinephalus malabaricus. Aquaculture 250:356-363.
Lin YH, Shiau SY, 2007. The effects of dietary selenium on the oxidative stress of grouper, Epinephelus malabaricus, fed high copper. Aquaculture, In press, doi:10.1016/j.aquaculture.2006.12.015
Lorentzen M, Maage A, Julshamn K, 1994. Effects of dietary selenite or selenomethionine on tissue selenium levels of Atlantic salmon (Salmo salar). Aquaculture 121:359-367
Lovell T, 1988. Nutrition and feeding of fish. Van Nostrand Reinhold, New York, USA, 260 pp.
Lovell RT, Wang CL, 1997. Comparison of organic and inorganic sources of selenium for growth and health of channel catfish. In: Biotechnology in the feed industry. Proceedings of Alltech's 13th Annual Symposium, eds, Lyons TP, Jacques KA, pp. 165-179.
Lyons MS de, 1998. Organic selenium as a supplement for Atlantic salmon: effects on meat quality. In: Biotechnology in the feed industry. Proceedings of Alltech's 14th Annual Symposium: passport to the year 2000, eds, Lyons TP, Jacques KA, pp. 505-508.
National Research Council (NRC) 1993. Nutrient requirements of fish. National Academy Press, Washington DC, USA, 114 pp.
Oberbach H, Hartfiel W, 1987. Auswirkungen unterschiedlicher α-Tocopherol- und Selenzusätze in Rationen mit hohen Gehalten an Polyensäuren auf Regenbogenforellen (Salmo gairdnerii, R.) [Effects of diets high in polyenoic acids and supplemented with different amounts of α-tocopherol and selenium on rainbow trout (Salmo gairdnerii)] Fett Wissenschaft Technologie 89:195-199.
Ogle RS, Knight AW, 1989. Effects of elemental foodborne selenium on growth and reproduction of the fathead minnow (Pimephales promelas). Archives of Environmental Contamination and Toxicology 18:795-803.
Palace VP, Spallholz JE, Holm J, Wautier K, Evan RE, Baron CL, 2004. Metabolism of selenomethionine by rainbow trout (Oncorhynchus mykiss) embryos can generate oxidative stress. Ecotoxicology and Environmental Safety 58:17-21.
Paripatananont T, Lovell RT, 1997. Comparative net absorption of chelated and inorganic trace minerals in channel catfish Ictalurus punctatus diets. Journal of the World Aquaculture Society 28:62–67.
Poston HA, Combs GF Jr, Leibovitz L, 1976. Vitamin E and selenium interrelations in the diet of Atlantic salmon (Salmo salar): gross, histological and biochemical deficiency signs. Journal of Nutrition 106:892-904.
Salte R, Asgard T, Liestol K, 1988. Vitamin E and selenium prophylaxis against “Hitra Disease” in farmed Atlantic salmon – a survival guide. Aquaculture 75:45-55.
Tashjian DH, The SJ, Sogomonyan A, Hung SSO, 2006. Bioaccumulation and chronic toxicity of dietary L-selenomethionine in juvenile white sturgeon (Acipenser transmontanus). Aquatic Toxicology 79:401-409. 
Teh SJ, Deng X, Deng DF, Teh FC, Hung SS, Fan TW, Liu J, Higashi RM, 2004. Chronic dietary selenium on juvenile Sacramento splittail Pogonichthys macrolepidotus. Environmental Science and Technology 38:6085-6093.
Thomas PM, Buchanan J, 2006. The use of dietary antioxidants to extend colour shelf life in farmed juvenile Southern Bluefin Tuna (Thunnus maccoyii). In: Nutritional biotechnology in the feed and food industries: Proceedings of Alltech's 22nd Annual Symposium, Lexington, Kentucky, USA, 23-26 April 2006, eds, Lyons TP, Jacques KA, Hower JM, pp. 453-460. 
Thorarinsson R, Landolt ML, Elliott DG, Pascho RJ, Hardy RW, 1994. Effect of dietary vitamin E and selenium on growth, survival and the prevalence of Renibacterium salmoninarum infection in chinook salmon (Oncorhynchus tshawytscha). Aquaculture 121: 343-358
Wang CL, Lovell RT, 1997. Organic selenium sources, selenomethionine and selenoyeast, have higher bioavailability than an inorganic selenium source, sodium selenite, in diets for channel catfish (Ictalurus punctatus). Aquaculture 152:223-234.
Wang CL, Lovell RT, Klesius PH, 1997. Response to Edwardsiella ictaluri by channel catfish fed organic and inorganic sources of selenium. Journal of Aquatic Animal Health 9:72-179.
Wise DJ, Tomasso JR, Gatlin DM III, Bai SC, Blazer VS, 1993. Effects of dietary selenium and vitamin E on red blood cell peroxidation, glutathione peroxidase activity and macrophage superoxide anion production in channel catfish. Journal of Aquatic Animal Health 5:177-182.

Article details

  • Author(s)
  • U. Allen
  • Date
  • 05 March 2007
  • Subject(s)
  • Animal nutrition