MYCOTOXINS IN AQUACULTURE: THE OCCURRENCE AND SIGNIFICANCE

The importance of mycotoxins to aquaculture first became apparent during the early 1960s with outbreaks of aflatoxicosis in hatchery-reared rainbow trout (Onchorhynchus mykiss) in the United States. Since that period, the concern about mycotoxins in aquaculture has been growing mainly due to the tendency to replace animal-derived proteins, such as fish meal, with plant-derived protein sources, due to limited supply and price increase of fish meal.

Over a period of two years (January 2014-December 2015), 52 samples of finished aquaculture feed for both shrimp and fish, were analyzed within the scope of the BIOMIN Mycotoxin Survey program. The samples were tested for aflatoxins (AF, sum of AFB1, AFB2, AFG1 and AFG2), zearalenone (ZEN), deoxynivalenol (DON), fumonisins (FB, sum of FB1 and FB2) and ochratoxin A. Samples were sourced in Asia (31 samples collected in 2014 and 21 samples collected in 2015) from animal farms or feed producers.

DON and AF were the most prevalent mycotoxins for 2014, with 68% of the samples testing positive, followed by ZEN and FB (58% positive). In 2015 we see a shift, with FB as the most prevalent mycotoxin followed by ZEN and DON. Concerning the average contamination levels, a decrease was observed for the 2015 samples. However when looking to the mycotoxin co-occurrence, the percentage of samples containing more than 1 mycotoxin increased from 84% to 90%, which raises the risk of synergistic effects of mycotoxins.

With the increasing substitution of fishmeal with plant feed ingredients in aquaculture feeds, the risk of mycotoxin contamination is real, as demonstrated by the present work. The reduced number of literature available on this topic often reports inconsistent results even for the same species, making it difficult to draw firm conclusions. However it is possible to observe that, according to literature, the detected levels of mycotoxins are within the sensitive levels of several Asian aquaculture species e.g., white leg shrimp, black shrimp and Nile tilapia. As we report, the rate of co-occurrence was high in 2014 and even higher in 2015, highlighting the risks of additive and synergistic effects. The present study shows that the decrease in the average mycotoxins contamination in samples from 2014 to 2015, does not necessarily mean a safer situation, due to the high percentage of mycotoxin co-occurrence.