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by Rui Gonçalves, Scientist Aquaculture and Michele Muccio, Product Manager Mycotoxins at Biomin

he global aquaculture industry’s rapid growth has been accompanied by a tandem rise in aquafeed production. In 2016, 39.9 million tons were produced (Reus, 2017). The future growth and sustainability of the industry depends on the ability of the sector to identify economically viable and environmentally friendly alternatives to marine derived ingredients, such as fishmeal and fish oil. A higher inclusion level of plant-based meals has been successfully achieved in several farmed species. Recently, Gonçalves et al. (2016) reported that mycotoxin levels in aquaculture-finished feeds, sampled in 2014, were high enough to present a danger to several important aquaculture species. The same was observed for samples sourced in Southeast Asia in 2015, even though contamination levels were lower compared to 2014. From 2014 to 2015, the number of detected mycotoxins per sample increased. This co-occurrence can be problematic, since certain combinations of mycotoxins can magnify the harm caused to animals.

Aflatoxins are not the only threat

A deeply entrenched belief across the aquaculture industry is that majority of mycotoxin issues are the result of poor on-farm storage conditions leading to aflatoxin contamination. While it remains true that the poor storage conditions can lead to the growth of Aspergillus sp. and Penicillium sp., which ultimately can lead to the production of aflatoxins (Afla) and ochratoxin A (OTA), the reality is that most of the mycotoxins found in finished feeds occur before storage (Figure 1). The main source of mycotoxin contamination is the raw materials used to produce aquafeeds. This was exactly what was shown by Gonçalves et al., (2017), which reported that in Asian samples, soybean meal, wheat, wheat bran, corn, corn gluten meal, rapeseed/canola meal and rice bran were mostly contaminated with Fusarium mycotoxins: zearalenone (ZEN), deoxynivalenol (DON) and fumonisins (FUM). The only exception was cottonseed meal, which was mainly contaminated

by aflatoxins together with Fusarium toxins (ZEN and DON) in considerable amounts. These results are extremely important and confirm that mycotoxin contamination found in finished feeds is related to the plant-based raw materials used to formulate these compound feeds.

2016 Mycotoxin Survey Results

Awareness of mycotoxin-related issues in the aquaculture industry has grown as feed manufacturers and producers realize the importance of mycotoxins other than aflatoxin and their potential to impact production. Over a period of one year (January 2016–December 2016), 14 samples of finished aquaculture feeds were analyzed within the scope of the BIOMIN Mycotoxin Survey program. Each sample was tested for 18 different mycotoxins. All finished feed samples were contaminated by mycotoxins. Fish feed samples (n=12) had in average five mycotoxins per sample and were mainly contaminated by FUM (averages of: FB1=249.11 μg/kg; FB2=96.86 μg/kg and FB3=38.29 μg/ kg); ZEN (75.67 μg/kg) and DON (110.50 μg/kg). These are considerably high average contamination levels (Figure 2). In addition, maximum occurrence levels reached 139 μg/kg for 15 AcDON, 396 μg/kg for DON and 708 μg/kg for fumonisin B1. Shrimp feeds (n=6) showed alarming high levels of DON with average values of 881.67 μg/kg and maximum occurrence of 2287 μg/kg of DON (Figure 3). These values are within the reported sensitivity levels of white leg shrimp, Litopenaeus vannamei, according to Trigo-Stockli et al., 2000—meaning that deoxynivalenol could pose a real threat to shrimp production.

How to fight Fusarium?

Fusarium mycotoxins are a broad class of compounds with different chemical structures, physical and toxicological proprieties. Due to this great diversity, different detoxification strategies are required to deal with this complex group of compounds. Adsorption is the most common approach to deal with mycotoxins and many products using this strategy are available on the market. However, as proved by several studies (Veikiru et al. 2015; Hahn et al. 2015; Fruhauf et al.

16 | April 2017 - International Aquafeed

APR 2017 - International Aquafeed magazine