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霉菌毒素对水产养殖的影响

来源: 赤峰和美嘉科技有限公司  点击:20 发布时间:2017-3-14

    霉菌毒素是谷物或饲料中霉菌生长产生的次级代谢产物,是各种植物和环境因素相关的应激反应或霉菌生长条件的改变造成的。在水产养殖业方面对霉菌毒素污染危害的认识已经越来越深人,不论是饲料生产企业还是鱼虾养殖者都认识到了霉菌毒素对水产动物健康和生产性能,以及产品质量的影响的严重性。霉菌毒素污染可降低鱼及农场饲养动物的生长率、饲料效率、繁殖性能及对传染病的抵抗力,并能引起肝脏及其他器官的损伤(Engelhardt等,1989;Thiel等,1992;Lumbertdacha等,1995)。本文综述了霉菌毒素对水产养殖危害的一些研究进展和控制方法。
1 霉菌毒素的危害
     尽管已知的霉菌毒素有几百种,主要的霉菌毒素有黄曲霉毒素、玉米赤霉烯酮、单端孢霉烯族毒素、烟曲霉毒素、赭曲霉毒素A和麦角生物碱6大类。根据其毒性和出现概率,对水产养殖最重要的霉菌毒素还是黄曲霉毒素。黄曲霉毒素是由黄曲霉和寄生曲霉产生的一类毒性极强、可致突变和致癌的物质(Deiner等,l987;Kurtzman等,1987)。产毒黄曲霉菌可产生黄曲霉毒素B1和B2,产毒寄生曲霉菌可产生黄曲霉毒素B1、B2、G1和G2(Cotty等,1994)。通常动物中毒的后果表现为生长缓慢、贫血、产生血液凝块、淤血、肝脏及一些器官受损、免疫功能降低、死亡率增加。玉米、花生、树生坚果、棉籽和其他食物的黄曲霉毒素污染,一直就是一个世界性问题。在全世界使用的很大一部分玉米是作为鱼类饲料的主要成分,据报道受污染后含有多达6 000μg/kg的黄曲霉毒素。花生仁和棉籽仁最容易受黄曲霉毒素污染,棉籽和玉米在蟹和鲶鱼中是常见的成分,而且占饲料配方中的25%~30%,因此黄曲霉毒素传染到鱼类的可能性较大。20世纪50年代末,整个美国和欧洲养殖的虹鳟发生了肝癌,发现与日粮配方中使用了霉变的棉籽仁有关(Wales,1970)。目前越来越多的研究表明,霉菌毒素对水产养殖种类的危害与陆生种类相似。近几年,很多的工作都是研究黄曲霉毒素对鱼类的危害,而仅有少量是研究霉菌毒素对其他种类比如虾类的危害。
     黄曲霉毒素B1对鱼的生物学影响与饲料中毒素水平及鱼的年龄和品种直接相关。有报道表明,不同鱼类对黄曲霉毒素(AFB)的敏感性差异很大(表1),鱼类对毒素的易感性依赖于其生长环境的温度,冷水鱼类对AFB1的易感性要低于暖水鱼类(Lovell,1989)。幼龄鱼类比成年鱼更易感。虹鳟鱼是对黄曲霉毒素最敏感的鱼种之一(Hendricks,1994),海水和淡水养殖的虹鳟鱼对AFB1都极为易感,因此有研究将虹鳟鱼作为检测环境致癌物的鱼模型。50g重的虹鳟鱼对黄曲霉毒素的半数致死量为500~1 000 μg/kg,其严重中毒的症状是:肝损坏、鳃变苍白、红细胞减少。而其他鱼类,如河鲇鱼,只有很高剂量才有影响,相比较罗非鱼对AFB1引起的生长抑制更为敏感(Jantrarotai & Lovell,1990;Jantrarotai等,1990)。如罗非鱼饲喂含0.2mg AFB/kg的日粮会导致16.7%死亡率(El-Banna等,1992),Nguyen等(2002)的研究结果显示10mg AFB/kg日粮饲喂8周可导致罗非鱼生长率下降90%。Y.S. El-Sayed等(2009)发现海水鲈鱼也表现出对AFB1的高度敏感,口服AFB1达96h的LC50为0.18mg/kg体重,急性中毒的鱼只表现为运动迟缓,平衡丧失,腮骨迅速翕动,背部皮肤表面出血。通过每日给予0.018mg/kg体重的AFB1,42d试验结束时,海水鲈鱼的血清转氨酶、碱性磷酸酶活性显著升高,血浆蛋白含量明显下降,且鱼体肌肉组织中AFB1残留高约5μg/kg。血液中谷草转氨酶(AST)、谷丙转氨酶(ALT)、碱性磷酸酶(ALP)活性增加,可能是由于肝、肾、心脏等器官坏死引起,是表现肝脏和肾脏损伤的重要指标。因此长期接触低剂量AFB1将会导致海水鲈鱼慢性中毒,导致动物消化酶活性降低,饲料转化率下降,从而引起动物生产性能的下降。有报道给白斑鱼每日饲喂50μg/kg的AFB1,30d后体内也可检测到5μg/kg的残留,鱼体中毒素残留增加了黄曲霉毒素向人类转移的风险。不过虾和罗非鱼饲喂很高剂量的AFB1 60d未检测到毒素残留,这可能是由于AFB1在这些物种中的代谢途径不同所导致。
* 96h测定值,其余为24h测定值。
盐水虾和淡水甲壳动物24h内对AFB1的半数致死浓度分别为14.0mg/L和1.0mg/L,对虾对AFB1的半数致死量为100.5mg/kg(Reiss,1972)。AFB1可引起海水虾生长不良,消化率低下,生理机能紊乱,以及组织学病变,主要是肝胰脏组织(Lightner等,1982;Lightner等,1988;Bautista等,1994;Ostrowski-Meissner等,1995;Boonyaratpalin等,2001;Bintvihok等,2003)。菲律宾学者发现虾饲料的霉菌毒素浓度在73.8μg/kg时虾生长缓慢,较容易得皮肤病,(甲壳动物)肝胰腺的损伤还会引发其他病情。梁萌青等人(1996)在探讨黄曲霉毒素对中国对虾生长的影响时发现,饲料中黄曲霉毒素B1的含量分别为472.0μg/kg、78.7μg/kg时,若以对照组为100,中国对虾成活率均为55%,增重率分别为43.9%、45.4%,消化率依次为79.4%和83.2%。对虾游泳缓慢,个别对虾在水面游泳,很少抱食,离水后即亡,不过其体内未检测到黄曲霉毒素。泰国学者研究发现给草虾分别饲喂含5,10,20μg/kg AFB1的饲粮,在7d和10d时,草虾体重分别降至初始重的46%和59%,肝胰腺也出现了损伤,AFB1可明显影响草虾的生长性能。
     其他霉菌毒素也可引起养殖鱼类的生产问题,但实验浓度远远高于实际生产中饲料当中的平均毒素浓度。研究表明可导致河鲇鱼生长抑制的烟曲霉毒素B1(FB1)最低浓度水平是20~40mg/kg,20mg FB1/kg饲喂2周会显著降低增重,而罗非鱼对FB1的敏感性则较低。河鲇鱼小鱼饲喂80mg FB1/kg时,增重为对照组的50%,罗非鱼饲喂70mg FB1/kg时,增重为对照组的71%。河鲇鱼和罗非鱼均可耐受日粮FB1水平为150mg/kg,在320或720mg FB1/kg时,才可观察到鱼的死亡。FB1单独存在时(104mg/kg,24周)未能诱导虹鳟发生肝癌,但与AFB1同时存在时,则可促进肝癌的发生(David等,2001)。相比较甲壳动物的敏感性要高很多,盐水虾24h内对FB1的半数致死浓度为60μg/kg(Jiménez等,1997)。脱氧雪腐镰刀菌烯醇简称DON,也就是常说的呕吐毒素,是由镰刀霉菌代谢产生的。当生长期处在潮湿天气时,在小麦中DON是一种很重要的毒素。喂养虹鳟鱼DON在0,1.0,2.0和5.0mg/kg浓度时,将减缓鱼类生长。当喂养虹鳟鱼的饲料浓度达到20mg DON/kg时,会发生拒食现象。但是DON对其余水产生物的影响则较少。关于玉米赤霉烯酮(ZEA)对水产生物影响的研究资料也很少见,Augustine等(1999)用虹鳟建立了一个模型用来评价ZEA及其代谢产物在体内的类雌激素效价,这表明ZEA同样会影响水生生物的生殖系统。但是喂养虹鳟和鲑鱼ZEA在1.0和10.0mg/kg体重浓度时,均未对动物表现出明显影响。赭曲霉毒素是主要由曲霉菌和青霉菌产生的毒素,它经常危害鱼类的肾脏,而且当其和其他毒素一起出现在饲料中,会加强其他毒素的危害。腹腔注射赭曲霉毒素A(OTA)对6月大虹鳟鱼的急性毒素引起的半致死量是4.67mg/kg(Doster等,1972),赭曲霉毒素对虹鳟鱼的危害有肝脏坏死,颜色变暗,肾脏肿大,死亡率变高等。河鲇鱼饲喂2.0,4.0或8.0mg/kg OTA 8周时,其生长率分别下降35%,66%,90%;4.0或8.0mg/kg OTA时,饲料转化率显著下降;8.0mg/kg OTA时,可导致河鲇鱼20%死亡。另外还观察到肝胰脏对日粮OTA的敏感性比肾脏更高,这意味着肝胰脏可能是OTA毒性的靶器官。
另外,一些霉菌和细菌会破坏饲料中的营养成分。比如,青霉菌属的霉菌能从叶酸的蝶酸中分解出谷氨酸,引起叶酸的缺乏,这一直被怀疑可能是引起河鲇鱼营养性贫血的原因。
2 霉菌毒素的预防

     一般来讲在用于鱼饲料的玉米和花生产品中,黄曲霉毒素的含量不能超过20μg/kg。由于用于鱼饲料的其他农产品的黄曲霉毒素允许含量还没有规定,因此,水产饲料制造商应该检测所有的与真菌毒素有关的原料。在生产鱼苗饲料时,应该避免使用哪怕是怀疑有微量黄曲霉毒素的原料,因为鱼苗的敏感性很高。控制收割后霉菌毒素污染的最佳方法是对饲料进行科学的贮存和加工。另外对饲料进行霉菌毒素分析、剔出受污染的饲料批次,对饲料进行处理以减少霉菌的生长、对受污染饲料进行稀释和处理从而降低霉菌毒素的浓度。一种被污染的饲料或其成分可能含有超过一种的霉菌毒素。许多研究报导指出,霉菌毒素具有协同作用,两种毒素综合起来的危害比单独作用的危害大得多。加热和粒化过程中的压挤并不能除去足够的毒素,尤其是黄曲霉毒素,它对热非常稳定,甚至在高温和蒸汽下受热也较稳定。吸附剂有助于减小霉菌毒素的影响,目前市场上霉菌毒素吸附剂的种类很多,吸附毒素效果的差别也很大,用户在使用时应该选择一些广谱高效并具有选择性吸附功能的产品。脱霉素(Novasil)是至今全球唯一在学报刊物发表证实具有选择性吸附特点,即只吸附毒素,不吸附主要营养物的代表产品,它可以选择性的吸附饲料中的黄曲霉毒素,而不会干扰饲料中维生素A、 β-胡萝卜素、磷等营养物质的吸收(Chung等,1990;Phillips等,1995)。研究发现饲料中添加脱霉素可保护锦鲤免受高剂量黄曲霉毒素B1(100μg/kg)的影响。


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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