Tuesday, September 1, 2015

01/09/2015: Biomin mycotoxin survey: Focus on the main risks in aquafeed

First published in International Aquafeed, July-August 2015

Aquaculture feeds have moved away from their dependence on fishmeal as the main protein source and now rely mainly on plant protein sources. How then will this affect mycotoxin exposure in aquatic animals?

With fishmeal and fish oil becoming increasingly expensive, the inclusion of terrestrial plantbased proteins in commercial aquaculture feeds has gained widespread acceptance. Even feeds for carnivorous species are now formulated to contain more than 50-70 percent of plant-derived matter.

A common problem that arises from the use of plant ingredients is the presence of mycotoxins - toxic secondary metabolites produced by filamentous fungi which frequently contaminate agricultural commodities.

Mycotoxins are mainly produced under warm and moist conditions typical of the tropical and subtropical countries where most aquaculture is practiced. Temperature resistant, mycotoxins are not destroyed by the heat and pressure of pelleting and extrusion.

Crop contamination over 25 percent
The Council for Agricultural Sciences and Technology (CAST) in 2003 estimated that 25 percent of the world's crop production was contaminated with mycotoxins.

Over the past 10 years of the Biomin Mycotoxin Survey, the evaluation of almost 33,000 samples from around the world revealed that more than three quarters of these samples were contaminated with at least one mycotoxin and 43 percent of all samples were co-contaminated with two or more toxins.

While in terrestrial animals the toxic effects of mycotoxins have been widely studied, the effects in aquatic   species have not yet been fully elucidated. However, several studies have reported the detrimental effects of mycotoxins at low levels.


For example, Pangasius fed diets contaminated with 60 parts per billion (ppb) aflatoxin suffer affects on their growth and increased liver damage. A different study, also with Pangasius, showed that at levels of 50ppb the fishes' resistance to challenge by the bacterium Edwardsiela ictaluri is reduced. Another study on yellow catfish with AFB1 levels above 250ppb showed increased feed conversion rate (FCR) and reduced weight gain. In shrimp, levels as low as 20ppb have been found to reduce weight gain.

Diets contaminated with 100ppb Zearalenone (ZEN) reduced weight and increased FCR in white shrimp, while survival was affected with ZEN levels above 1000ppb.

Deoxynivalenol, one of the most common mycotoxins, is highly toxic to rainbow trout: reduction of feed efficiency and growth occurs at levels of 1ppm. Salmon feed contaminated with 3.6 parts per million (ppm) caused a 20 percent reduction in feed intake and an 18 percent increase in FCR. Long-term exposure effects of fumonisin B1 (FB1) reported in carp showed that exposure to 0.5 and 5.0mg per kg body weight is not lethal to young carp, but can produce adverse physiological effects with kidney and liver being the key target organs for FB1 action.

Aquafeed samples contaminated
In the Biomin Mycotoxin Survey 2014, the main ingredients intended for the aquaculture industry including corn, corn DDGS, soybean meal, wheat, wheat bran and rice bran were evaluated. The five most common mycotoxins found worldwide—aflatoxins (Afla), zearalenone (ZEN), deoxynivalenol (DON), T-2 toxin (T-2), fumonisins (FUM) and ochratoxin A (OTA)— were analysed in all of the samples (see Table 1). In addition, a specific survey which included 41 aquafeed samples (fish/ shrimp) from the Asian region was included.

More than three-quarters of the aquafeed samples were co-contaminated with two mycotoxins or more and 93 percent of samples contained at least one mycotoxin. The highest incidence was observed for DON at 68 percent, followed by ZEN and Afla at 59 percent each. The average Afla concentration was 49ppb, a level that poses a health risk to aqua species. One aquafeed sample contained FUM at 7534ppb.

Corn samples contained the highest average and maximum concentrations of Afla, ZEN, DON and FUM among all samples. As expected, DON and FUM were the most frequently found mycotoxins in corn with a prevalence of 72 percent each, followed by ZEN at 55 percent.

The highest Afla, DON and FUM prevalence was observed in corn DDGS. The highest average level and maximum concentration of OTA was determined in soybean meal samples at 24ppb and 141ppb respectively. DON is the most common mycotoxin found in wheat samples with an incidence of 56 percent. The highest average T-2 level was detected in wheat samples at 100ppb. The highest incidence of DON among all samples was determined in wheat bran samples. The highest prevalence of Afla (40 percent) was determined in rice bran.

Mycotoxin analyses in this survey clearly indicate that constant monitoring of mycotoxins is important. An effective mycotoxin risk management program is essential in order to protect animals from the negative impacts of mycotoxins on their health and performance.   

Read the magazine HERE.

The Aquaculturists
This blog is maintained by The Aquaculturists staff and is supported by the
magazine International Aquafeed which is published by
Perendale Publishers Ltd

For additional daily news from aquaculture around the world: aquaculture-news

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