Mycotoxins are a diverse group of toxic secondary metabolites produced mainly by filamentous fungi, on agricultural products before or after harvest, during transportation or storage. Research characterizing the adverse effects of mycotoxins on the performance and health of animals has largely focused on terrestrial livestock species (D’Mello and Macdonald, 1997; Rotter et al., 1996). However, in recent years, research has been carried out on the effects of mycotoxins in aquaculture species. Understanding these effects has become even more important with the rising cost of fishmeal and the need to identify and use more economical protein sources such as plant protein or other commercially available plant by-products.
Generally, most of the mycotoxins that have the potential to reduce growth and compromise the health status of aquaculture farmed animals are produced by Aspergillus, Penicillium and Fusarium species. Toxic metabolites produced by these fungi are known to be either carcinogenic (e.g. aflatoxin (AF) B1, ochratoxin A (OTA), fumonisin (FUM) B1), estrogenic (zearalenone (ZEN)), neurotoxic (FUM B1), nephrotoxic (ochratoxin), dermatotoxic (trichothecenes) or immunosuppressive (AFB1, OTA and T-2 toxin). The tendency, and the economic need, to replace expensive animal-derived proteins such as fishmeal, with less expensive plant protein sources, has increased the impact of mycotoxin contamination in aquaculture feeds (Gonçalves et al., 2017).
Materials & methods
From January to June 2017, 8,345 samples of plant meals were analysed 33,370 times within the scope of the BIOMIN Mycotoxin Survey Program (Table 1). The study focused on corn, corn gluten meal, corn DDGS, soybean meal, wheat, wheat bran rice and rice bran. The samples were tested for aflatoxins (sum of AFB1, AFB2, AFG1 and AFG2), ZEN, deoxynivalenol (DON), FUM (sum of FB1 and FB2), T-2 toxin and OTA (full toxin screen). Sample providers were instructed to follow good sampling procedures according to Richard (2000). The analyses were carried out as described by Binder et al., (2007).
Table 1. Origin of samples.
|Location||Number of samples|
Globally, Fusarium mycotoxins were the most prevalent compounds found in the samples, followed by aflatoxins. Some of the plant meals that are commonly used in aquaculture feeds, such as corn gluten meal and corn DDGS, showed high levels of mycotoxin contamination, commonly with DON and FUM. The results are presented in Table 2. Mycotoxin co-occurrence was generally very high; on average, 74% of the samples contained more than one mycotoxin.
Table 2. Analysis results.
|Average (μg/kg)||Maximum (μg/kg)|
|Corn gluten meal||2,250||1,688||11,882||8,871|
Deoxynivalenol, one of the most prevalent mycotoxins in the samples analysed, is known to cause adverse effects in several aquatic species, but especially rainbow trout (Oncorhynchus mykiss) (Hooft et al., 2011).
DON is responsible for decreases in growth, feed intake, feed efficiency, protein and energy utilization. The levels of DON found in some commodities might represent a threat for aquaculture species, depending on the inclusion levels of the plant meals in the finished feeds. FUM, also very prevalent among the collected samples, was found in considerably high concentrations, especially in corn gluten meal and corn DDGS.
Fumonisins inhibit the sphinganine (sphingosine) N-acyltransferase (ceramide synthase), a key enzyme in lipid metabolism, resulting in the disruption of this pathway. It is known that rainbow trout liver is sensitive to FUM, inducing changes in sphingolipid metabolism even when contamination levels are lower than 100 μg/kg (Meredith et al., 1998) and inducing cancer in one-month old trout (Riley et al., 2001).
Crustaceous can be very sensitive to FUM as well, being reported that Litopenaeus vannamei are sensitive to FB1 at levels below 200 μg/kg (García-Morales et al., 2013).
The contamination levels found in plant meals commonly used in aquaculture were high, and in 74% of samples there were two or more mycotoxins present, potentially leading to additive or synergistic effects. These results highlight the mycotoxin-related risks associated with growth performance and immunosuppression that can lead to significant economic impacts in the aquaculture sector.