56 MARCH 2016 • WORLD AQUACULTURE • WWW.WAS.ORG In 2003, the Council for Agricultural Science and Technology estimated that mycotoxin contamination affected nearly 25 percent of global crop production, making it the most important category of biological toxins impacting human and animal health. More recently, the 2014 BIOMIN Mycotoxin Survey reported mycotoxin contamination in 66 percent of crops tested, with average contamination levels of 1394 ppb. Mycotoxins are found mainly in agricultural commodities and are produced at various stages, before or after harvest, during transportation or storage. With the recent trend to replace animal protein sources, such as fishmeal, with plant protein sources, the risk of mycotoxin contamination in aquafeeds increases in step with the more widespread use of plant materials in aquafeeds. According to the 2014 BIOMIN Mycotoxin Survey data from Asia, spanning January to December 2014, 31 samples of finished aquafeed for shrimp and farmed fish revealed widespread mycotoxin contamination. Aflatoxins including aflatoxin B1 (AFB1) were found on 21 samples, or 68 percent of samples tested. AFB1 reached a maximum concentration level of 221 ppb. In aquaculture, aflatoxins are the most studied mycotoxin. Aflatoxins in aquaculture were first found in 1960 in California, where aflatoxin-contaminated cottonseed meal caused an outbreak of aflatoxicosis in hatchery-reared rainbow trout Onchorhynchus mykiss. Scientific articles have been published on the toxicity of aflatoxins in fish and crustacean species, including • Rainbow trout Oncorhynchus mykiss • Channel catfish Ictalurus punctatus • Nile tilapia Oreochromis niloticus • Rohu Labeo rohita • European seabass Dicentrarchus labrax • Gibel carp Carassius auratus gibelio • Penaeid shrimp Counteracting the Negative Effects of Aflatoxins Several methods have been tested to attempt to decrease the bioavailability of aflatoxins. The addition of mycotoxin binders to contaminated diets is considered the most common approach to reduce effects of some mycotoxins. Binders decontaminate aflatoxins by binding (adsorbing) them strongly enough to prevent toxic interactions with the animal and to prevent mycotoxin absorption across the digestive tract. Several potential adsorbent materials have been tested, including activated carbon, aluminosilicates (clay, bentonite, montmorillonite, zeolite and phyllosilicates), complex indigestible carbohydrates (cellulose, polysaccharides from cell walls of yeast and bacteria such as glucomannans, peptidoglycans, and others), and synthetic polymers (cholestyramine, polyvinylpyrrolidone and derivatives). However, binding efficacy strongly differs according to the specific binder, its source and the chemical structure of the mycotoxin. Additionally, some binders can have negative effects on growth due to influence on nutrient utilization and mineral absorption. Counteracting the Effects of Mycotoxin Contamination in Yellow Catfish Yellow catfish Pelteobagrus fulvidraco is an important commercial freshwater species in China, with promising market potential in China, Japan, South Korea, and across East and South Asia. Due to its high market value, yellow catfish farming has increased rapidly in recent years. As an omnivorous freshwater fish from a subtropical area, the probability of being affected by aflatoxin-contaminated feedstuffs is large. Recently, Dr. Xinxia and colleagues1 studied the sensitivity of yellow catfish to dietary AFB1 contamination and the efficiency of Mycofix® Secure (BIOMIN Holding GmbH, AFLATOXINS: a Threat to Yellow Catfish Production Rui Gonçalves FIGURE 1. Weight gain (g) of yellow catfish at the end of the experiment. The risk of mycotoxin contamination in aquafeeds increases in step with the more widespread use of plant materials in aquafeeds. Samples of finished aquafeed for shrimp and farmed fish in Asia revealed widespread mycotoxin contamination. The addition of mycotoxin binders to contaminated diets is considered the most common approach to reduce effects of some mycotoxins.
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