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      霉菌毒素對水產養殖的影響

      來源: 赤峰和美嘉科技有限公司  點擊:20 發布時間:2017-3-14

          霉菌毒素是谷物或飼料中霉菌生長產生的次級代謝產物,是各種植物和環境因素相關的應激反應或霉菌生長條件的改變造成的。在水產養殖業方面對霉菌毒素污染危害的認識已經越來越深人,不論是飼料生產企業還是魚蝦養殖者都認識到了霉菌毒素對水產動物健康和生產性能,以及產品質量的影響的嚴重性。霉菌毒素污染可降低魚及農場飼養動物的生長率、飼料效率、繁殖性能及對傳染病的抵抗力,并能引起肝臟及其他器官的損傷(Engelhardt等,1989;Thiel等,1992;Lumbertdacha等,1995)。本文綜述了霉菌毒素對水產養殖危害的一些研究進展和控制方法。
      1 霉菌毒素的危害
           盡管已知的霉菌毒素有幾百種,主要的霉菌毒素有黃曲霉毒素、玉米赤霉烯酮、單端孢霉烯族毒素、煙曲霉毒素、赭曲霉毒素A和麥角生物堿6大類。根據其毒性和出現概率,對水產養殖最重要的霉菌毒素還是黃曲霉毒素。黃曲霉毒素是由黃曲霉和寄生曲霉產生的一類毒性極強、可致突變和致癌的物質(Deiner等,l987;Kurtzman等,1987)。產毒黃曲霉菌可產生黃曲霉毒素B1和B2,產毒寄生曲霉菌可產生黃曲霉毒素B1、B2、G1和G2(Cotty等,1994)。通常動物中毒的后果表現為生長緩慢、貧血、產生血液凝塊、淤血、肝臟及一些器官受損、免疫功能降低、死亡率增加。玉米、花生、樹生堅果、棉籽和其他食物的黃曲霉毒素污染,一直就是一個世界性問題。在全世界使用的很大一部分玉米是作為魚類飼料的主要成分,據報道受污染后含有多達6 000μg/kg的黃曲霉毒素;ㄉ屎兔拮讶首钊菀资茳S曲霉毒素污染,棉籽和玉米在蟹和鯰魚中是常見的成分,而且占飼料配方中的25%~30%,因此黃曲霉毒素傳染到魚類的可能性較大。20世紀50年代末,整個美國和歐洲養殖的虹鱒發生了肝癌,發現與日糧配方中使用了霉變的棉籽仁有關(Wales,1970)。目前越來越多的研究表明,霉菌毒素對水產養殖種類的危害與陸生種類相似。近幾年,很多的工作都是研究黃曲霉毒素對魚類的危害,而僅有少量是研究霉菌毒素對其他種類比如蝦類的危害。
           黃曲霉毒素B1對魚的生物學影響與飼料中毒素水平及魚的年齡和品種直接相關。有報道表明,不同魚類對黃曲霉毒素(AFB)的敏感性差異很大(表1),魚類對毒素的易感性依賴于其生長環境的溫度,冷水魚類對AFB1的易感性要低于暖水魚類(Lovell,1989)。幼齡魚類比成年魚更易感。虹鱒魚是對黃曲霉毒素最敏感的魚種之一(Hendricks,1994),海水和淡水養殖的虹鱒魚對AFB1都極為易感,因此有研究將虹鱒魚作為檢測環境致癌物的魚模型。50g重的虹鱒魚對黃曲霉毒素的半數致死量為500~1 000 μg/kg,其嚴重中毒的癥狀是:肝損壞、鰓變蒼白、紅細胞減少。而其他魚類,如河鲇魚,只有很高劑量才有影響,相比較羅非魚對AFB1引起的生長抑制更為敏感(Jantrarotai & Lovell,1990;Jantrarotai等,1990)。如羅非魚飼喂含0.2mg AFB/kg的日糧會導致16.7%死亡率(El-Banna等,1992),Nguyen等(2002)的研究結果顯示10mg AFB/kg日糧飼喂8周可導致羅非魚生長率下降90%。Y.S. El-Sayed等(2009)發現海水鱸魚也表現出對AFB1的高度敏感,口服AFB1達96h的LC50為0.18mg/kg體重,急性中毒的魚只表現為運動遲緩,平衡喪失,腮骨迅速翕動,背部皮膚表面出血。通過每日給予0.018mg/kg體重的AFB1,42d試驗結束時,海水鱸魚的血清轉氨酶、堿性磷酸酶活性顯著升高,血漿蛋白含量明顯下降,且魚體肌肉組織中AFB1殘留高約5μg/kg。血液中谷草轉氨酶(AST)、谷丙轉氨酶(ALT)、堿性磷酸酶(ALP)活性增加,可能是由于肝、腎、心臟等器官壞死引起,是表現肝臟和腎臟損傷的重要指標。因此長期接觸低劑量AFB1將會導致海水鱸魚慢性中毒,導致動物消化酶活性降低,飼料轉化率下降,從而引起動物生產性能的下降。有報道給白斑魚每日飼喂50μg/kg的AFB1,30d后體內也可檢測到5μg/kg的殘留,魚體中毒素殘留增加了黃曲霉毒素向人類轉移的風險。不過蝦和羅非魚飼喂很高劑量的AFB1 60d未檢測到毒素殘留,這可能是由于AFB1在這些物種中的代謝途徑不同所導致。
      * 96h測定值,其余為24h測定值。
      鹽水蝦和淡水甲殼動物24h內對AFB1的半數致死濃度分別為14.0mg/L和1.0mg/L,對蝦對AFB1的半數致死量為100.5mg/kg(Reiss,1972)。AFB1可引起海水蝦生長不良,消化率低下,生理機能紊亂,以及組織學病變,主要是肝胰臟組織(Lightner等,1982;Lightner等,1988;Bautista等,1994;Ostrowski-Meissner等,1995;Boonyaratpalin等,2001;Bintvihok等,2003)。菲律賓學者發現蝦飼料的霉菌毒素濃度在73.8μg/kg時蝦生長緩慢,較容易得皮膚病,(甲殼動物)肝胰腺的損傷還會引發其他病情。梁萌青等人(1996)在探討黃曲霉毒素對中國對蝦生長的影響時發現,飼料中黃曲霉毒素B1的含量分別為472.0μg/kg、78.7μg/kg時,若以對照組為100,中國對蝦成活率均為55%,增重率分別為43.9%、45.4%,消化率依次為79.4%和83.2%。對蝦游泳緩慢,個別對蝦在水面游泳,很少抱食,離水后即亡,不過其體內未檢測到黃曲霉毒素。泰國學者研究發現給草蝦分別飼喂含5,10,20μg/kg AFB1的飼糧,在7d和10d時,草蝦體重分別降至初始重的46%和59%,肝胰腺也出現了損傷,AFB1可明顯影響草蝦的生長性能。
           其他霉菌毒素也可引起養殖魚類的生產問題,但實驗濃度遠遠高于實際生產中飼料當中的平均毒素濃度。研究表明可導致河鲇魚生長抑制的煙曲霉毒素B1(FB1)最低濃度水平是20~40mg/kg,20mg FB1/kg飼喂2周會顯著降低增重,而羅非魚對FB1的敏感性則較低。河鲇魚小魚飼喂80mg FB1/kg時,增重為對照組的50%,羅非魚飼喂70mg FB1/kg時,增重為對照組的71%。河鲇魚和羅非魚均可耐受日糧FB1水平為150mg/kg,在320或720mg FB1/kg時,才可觀察到魚的死亡。FB1單獨存在時(104mg/kg,24周)未能誘導虹鱒發生肝癌,但與AFB1同時存在時,則可促進肝癌的發生(David等,2001)。相比較甲殼動物的敏感性要高很多,鹽水蝦24h內對FB1的半數致死濃度為60μg/kg(Jiménez等,1997)。脫氧雪腐鐮刀菌烯醇簡稱DON,也就是常說的嘔吐毒素,是由鐮刀霉菌代謝產生的。當生長期處在潮濕天氣時,在小麥中DON是一種很重要的毒素。喂養虹鱒魚DON在0,1.0,2.0和5.0mg/kg濃度時,將減緩魚類生長。當喂養虹鱒魚的飼料濃度達到20mg DON/kg時,會發生拒食現象。但是DON對其余水產生物的影響則較少。關于玉米赤霉烯酮(ZEA)對水產生物影響的研究資料也很少見,Augustine等(1999)用虹鱒建立了一個模型用來評價ZEA及其代謝產物在體內的類雌激素效價,這表明ZEA同樣會影響水生生物的生殖系統。但是喂養虹鱒和鮭魚ZEA在1.0和10.0mg/kg體重濃度時,均未對動物表現出明顯影響。赭曲霉毒素是主要由曲霉菌和青霉菌產生的毒素,它經常危害魚類的腎臟,而且當其和其他毒素一起出現在飼料中,會加強其他毒素的危害。腹腔注射赭曲霉毒素A(OTA)對6月大虹鱒魚的急性毒素引起的半致死量是4.67mg/kg(Doster等,1972),赭曲霉毒素對虹鱒魚的危害有肝臟壞死,顏色變暗,腎臟腫大,死亡率變高等。河鲇魚飼喂2.0,4.0或8.0mg/kg OTA 8周時,其生長率分別下降35%,66%,90%;4.0或8.0mg/kg OTA時,飼料轉化率顯著下降;8.0mg/kg OTA時,可導致河鲇魚20%死亡。另外還觀察到肝胰臟對日糧OTA的敏感性比腎臟更高,這意味著肝胰臟可能是OTA毒性的靶器官。
      另外,一些霉菌和細菌會破壞飼料中的營養成分。比如,青霉菌屬的霉菌能從葉酸的蝶酸中分解出谷氨酸,引起葉酸的缺乏,這一直被懷疑可能是引起河鲇魚營養性貧血的原因。
      2 霉菌毒素的預防

           一般來講在用于魚飼料的玉米和花生產品中,黃曲霉毒素的含量不能超過20μg/kg。由于用于魚飼料的其他農產品的黃曲霉毒素允許含量還沒有規定,因此,水產飼料制造商應該檢測所有的與真菌毒素有關的原料。在生產魚苗飼料時,應該避免使用哪怕是懷疑有微量黃曲霉毒素的原料,因為魚苗的敏感性很高?刂剖崭詈竺咕舅匚廴镜淖罴逊椒ㄊ菍︼暳线M行科學的貯存和加工。另外對飼料進行霉菌毒素分析、剔出受污染的飼料批次,對飼料進行處理以減少霉菌的生長、對受污染飼料進行稀釋和處理從而降低霉菌毒素的濃度。一種被污染的飼料或其成分可能含有超過一種的霉菌毒素。許多研究報導指出,霉菌毒素具有協同作用,兩種毒素綜合起來的危害比單獨作用的危害大得多。加熱和;^程中的壓擠并不能除去足夠的毒素,尤其是黃曲霉毒素,它對熱非常穩定,甚至在高溫和蒸汽下受熱也較穩定。吸附劑有助于減小霉菌毒素的影響,目前市場上霉菌毒素吸附劑的種類很多,吸附毒素效果的差別也很大,用戶在使用時應該選擇一些廣譜高效并具有選擇性吸附功能的產品。脫霉素(Novasil)是至今全球唯一在學報刊物發表證實具有選擇性吸附特點,即只吸附毒素,不吸附主要營養物的代表產品,它可以選擇性的吸附飼料中的黃曲霉毒素,而不會干擾飼料中維生素A、 β-胡蘿卜素、磷等營養物質的吸收(Chung等,1990;Phillips等,1995)。研究發現飼料中添加脫霉素可保護錦鯉免受高劑量黃曲霉毒素B1(100μg/kg)的影響。


      The English version

      Mycotoxin is mold growth in grain or feed to produce secondary metabolites, is all kinds of plants and environmental factors related to the change of stress reaction or mold growth conditions. In aquaculture industry has become increasingly deep understanding of mycotoxin contamination hazards, both feed production enterprise and fish and shrimp farmers have realized the mycotoxin on aquatic animal health and production performance, and the seriousness of the quality of products. Mycotoxin contamination can reduce the growth rate of fish and farm animals, feed efficiency, reproductive performance and resistance to infectious diseases, and can lead to liver and other organ damage (Engelhardt said, etc., 1989; Thiel, etc., 1992; Lumbertdacha etc., 1995). Mycotoxin was reviewed in this paper some research progress about the danger of aquaculture and the control method. 1 the dangers of mycotoxin despite hundreds of mycotoxin known, main mycotoxins of aflatoxin, corn gibberellic ketene, single-ended spore aspergillus toxin alkene toxins, smoke, ochratoxin A 6 types and ergot alkaloids. According to its toxicity and the occurrence probability, the most important thing for aquaculture mycotoxin aflatoxin. Yellow aspergillus toxin is produced by aspergillus flavus and parasitic aspergillus kind of highly toxic, mutagenic and carcinogenic substances (Deiner, l987; Kurtzman, etc., 1987). Enterotoxigenic yellow aspergillus can produce aflatoxin B1 and B2, the toxin-producing parasitic aspergillus can produce aflatoxin B1, B2, G1 and G2 (Cotty etc., 1994). Consequences of animal poisoning is usually slow-growing, anemia, blood clots, blood, liver and some organ damage, reduced immune function and increased mortality. Corn, peanuts, tree nuts, seeds and other aflatoxin contamination of food, has always been a worldwide problem. In a large part of the world use corn as the main composition of fish feed, according to the report after contaminated contain as many as 6, 000 mu g/kg of aflatoxin. Peanut, and cottonseed most susceptible to aflatoxin contamination, cottonseed and corn is a common ingredient in the crab and catfish, and accounts for 25% ~ 30% of feed formulation, therefore aflatoxins are more likely to infect to fish. In the late 1950 s, the United States and Europe farmed steelhead liver cancer, found that Japanese food formula were used in the mould of cottonseed (Wales, 1970). Currently, more and more studies show that mycotoxin and terrestrial species are similar to the harm of aquaculture species. In recent years, a lot of work is to study the aspergillus flavus toxin harm to fish, and only a small amount is the study of the mold toxin harm to other species such as shrimp. Aflatoxin B1 and effects on fish biology toxin levels in feed and directly related to the age and varieties of fish. Reports have indicated that the sensitivity of different fish on aflatoxin (AFB) difference is very big (table 1), fish susceptibility to the toxin is dependent on its growing environment temperature, cold water fish susceptibility of AFB1 than warm water fish (Lovell, 1989). The young fish more susceptible than adult fish. Rainbow trout is one of the most sensitive species of aflatoxin (Hendricks, 1994), seawater and freshwater aquaculture of rainbow trout is extremely susceptible to AFB1, therefore studies the rainbow trout as testing fish model of environmental carcinogens. 50 g of rainbow trout median lethal dose of aflatoxin is 500 ~ 1 000 mu g/kg, its severe poisoning symptoms are: liver damage, gill pale, red blood cells. And other fish, such as river catfish, only high doses, compared with tilapia is more sensitive to growth inhibition caused by AFB1 (Jantrarotai & Lovell, 1990; Jantrarotai etc., 1990). Such as tilapia fed diet containing 0.2 AFB mg/kg can lead to a 16.7% mortality rate (El - Banna, etc., 1992), Nguyen, etc. (2002), the results showed that 10 mg AFB/kg diet feeding 8 weeks can lead to tilapia growth rate fell by 90%. Y.S. El - Sayed etc. (2009) found that the water of the sea bass also show that the sensitivity to the height of AFB1, oral AFB1 96 h LC50 is 0.18 mg/kg body weight, acute poisoning fish only show the bradykinesia, loss of balance, jawbone moved quickly, the back surface of the skin. By daily AFB1 of 0.018 mg/kg body weight, 42 d test at the end of the sea bass significantly increased serum aminotransferase, alkaline phosphatase activity of plasma protein content decreased obviously, and the fish muscle tissue of AFB1 residual high about 5 mu g/kg. Blood aspertate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) activity increased, may be due to the liver, kidney, heart and other organs caused necrosis, is an important index of liver and kidney damage. So long-term exposure to low doses of AFB1 will lead to chronic poisoning, sea bass results in the decrease of animal digestive enzyme activity, feed conversion rate decreased, causing decline in animal production performance. Reports to the grouper daily feeding 50 mu g/kg of AFB1, after 30 d can also be detected in the body 5 mu g/kg of residual, fish toxin residue increased the risk of aflatoxin to humans. But shrimp and tilapia fed high doses of AFB1 60 d toxins residue was detected, this may be due to AFB1 are different in the metabolic pathway of these species.

      * 96 h measurements, the rest of the determination value of 24 h. Brine shrimp and freshwater crustaceans within 24 h of AFB1 median lethal concentration were 14.0 mg/L and 1.0 mg/L, shrimp of AFB1 median lethal dose of 100.5 mg/kg (Reiss, 1972). AFB1 can cause poor seawater shrimp growth, digestive rate is low, the physiological function disorder, and the histologic lesions, mainly liver pancreas tissue (Lightner etc., 1982; Lightner etc., 1988; Bautista, etc., 1994; Meissner Ostrowski, 1995; Boonyaratpalin etc., 2001; Bintvihok etc., 2003). The Philippines scholars found that the shrimp feed mycotoxins concentration in 73.8 mu g/kg, slow growth of the shrimp is prone to skin diseases, liver injury of the pancreas (crustaceans) will cause other illness. Meng-qing liang et al. (1996) on aflatoxin's influence on the growth of penaeus chinensis, content of aflatoxin B1 in feed were 472.0 mu g/kg, 78.7 mu g/kg, if in the control group of 100, the Chinese prawn survival rate is 55%, weight gain rate is 43.9%, 45.4% respectively, digestion rate of 79.4% and 83.2% in turn. Individual prawn shrimp swimming slowly, swimming in the water, rarely have food, away from the water after the death, but the body not detected aflatoxin. Thai scholars study found to shrimp fed respectively containing 5,10,20 mu g/kg of AFB1 fodder, 7 d and 10 d, shrimp weight dropped to 46% of the initial weight and 46% respectively, also appeared liver pancreas injury, AFB1 can significantly influence the growth performance of the shrimp. Other mycotoxin also can cause the production problems of farmed fish, but the concentration is much higher than in the actual production of feed the average concentration of toxin. Research shows that can lead to river catfish growth inhibition of smoke aspergillus toxin B1 (FB1) minimum levels is 20 ~ 40 mg/kg, 20 FB1 mg/kg feeding two weeks will be significantly reduced weight gain, while the susceptibility of FB1 to tilapia is low. River catfish fish feeding 80 FB1 mg/kg, the weight is 50% in the control group, tilapia fed 70 FB1 mg/kg, the weight gain of 71% in the control group. River catfish and tilapia diet FB1 can tolerance level of 150 mg/kg, in 320 or 720 mg FB1 / kg, can only be observed in the death of fish. FB1 exist alone (104 mg/kg, 24 weeks) failed to induce steelhead liver cancer, but with the AFB1 exist at the same time, can promote the occurrence of cancer of the liver (David, 2001). Compared with crustaceans of the sensitivity of much higher, brine shrimp within 24 h of FB1 median lethal concentration of 60 mu g/kg (Jimenez, etc., 1997). DNA snow sickle bacterium enol DON for short, is often said that vomiting toxins, is produced by metabolism of knife mold. When growing in wet weather, in wheat DON toxin is a kind of very important. Rainbow trout fed DON in 0,1.0, 2.0 and 5.0 mg/kg concentration, growth will slow fish. When feeding the rainbow trout feed concentration reaches 20 DON mg/kg, no phenomenon happens. But DON is less impact on the rest of the aquatic organisms. Gibberellic ketene on corn (ZEA) impact on the aquatic biological research data is also very rare, such as Augustine (1999) with rainbow trout has set up a model used to evaluate the class ZEA and its metabolites in the body estrogen potency, suggesting that the reproductive system of ZEA will also affect aquatic organisms. But the trout and salmon feed ZEA in 1.0 and 10.0 mg/kg body weight concentration, were not showed obvious influence to animals. Ochre and aspergillus toxin is the main toxins produced by aspergillus and penicillium, it often harm fish kidney, and when it appeared in the feed, together with other toxins will strengthen the dangers of other toxins. Intraperitoneal injection of ochratoxin A (OTA) caused by acute poison big rainbow trout in June half lethal dose is 4.67 mg/kg (Doster, etc., 1972), ochre and aspergillus toxin to the harm of rainbow trout have liver necrosis, dark, renal enlargement, mortality is higher. River catfish feeding 2.0, 4.0 or 4.0 mg/kg OTA at 8 weeks, the growth rate fell 35%, 66%, 90%; 4.0 or 8.0 mg/kg OTA, feed conversion rate dropped significantly. When 8.0 mg/kg OTA, but led to the deaths of 20% river catfish. Also observed liver pancreas of diet OTA sensitivity is higher than the kidney, which means that the liver pancreas may be OTA toxic target organs. In addition, some fungi and bacteria break down the ingredients in feed. Penicillium mold can, for example, from the adjustment of folic acid in the acid decomposition of glutamic acid, cause the lack of folic acid, which has long been suspected may be the cause of nutritional anemia walking fish river. 2 mycotoxin prevention in general in maize and peanut products used in fish feed, the content of aflatoxin should not exceed 20 mu g/kg. Because of other agricultural products for fish feed aflatoxin allows content have not rules, therefore, aquatic feed manufacturers should be testing all the materials related to the mycotoxin. In the production of fish feed, should avoid to use trace raw materials of aflatoxin, even if it is suspected because of the high sensitivity of larvae. Control mycotoxin contamination after the harvest is the best way to feed for scientific storage and processing. In addition to feed mycotoxin analysis, singling out the contaminated feed batch, to deal with feed in order to reduce the growth of mold, to dilute the contaminated feed and processing so as to reduce the concentration of the mycotoxin. A kind of contaminated feed or its components may contain more than one mycotoxin. Many research reports, mycotoxins have synergy, combination of two kinds of toxin harm is much bigger than the harm of separate function. In the process of heating and granulating extrusion is not enough to remove the toxins, especially aspergillus flavus toxin, it is very stable to heat, even under high temperature and steam heating is relatively stable. Adsorbent is helpful to reduce the influence of mycotoxin, currently on the market, many different kinds of mycotoxins adsorbent, adsorption poison effect difference is very big also, users should choose in the use of some broad spectrum efficient and selective adsorption function of the product. Take off the drug (Novasil) is still the only global publications in the journal confirmed that selective adsorption characteristics, namely only absorb toxins, not on behalf of the main nutrient absorption of products, it can feed of selective adsorption of aflatoxin, and not interfere with the feed in vitamin A, beta-carotene, phosphorus and other nutrients absorption (Chung, etc., 1990; such as Phillips, 1995). Study found that take off the drug is added to the feed, can protect the brocade carp from high doses of aflatoxin B1 (100 mu g/kg).


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