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Dangerous Toxins Threaten Aquaculture on a Global Scale

Anater, Amanda, et al. “Mycotoxins and their consequences in aquaculture: A review.” Aquaculture 451 (2016): 1-10.

Fish is consumed globally. It is available and it is affordable, relative to the other meat types. Globally fish account for about 15% of the total consumed protein, and in developing countries the consumption of fish accounts for almost half of the protein.    In present day, aquaculture supplies almost half of fish consumed (Figure 1).  As global population continues to increase the dependence on aquaculture to meet the global demand will become stronger.

Aquaculture has become increasingly important to meeting the demand of fish my consumers globally (source: https://en.wikipedia.org/wiki/Aquaculture)

Figure 1: Aquaculture has become increasingly important to meeting the demand of fish my consumers globally (source: https://en.wikipedia.org/wiki/Aquaculture)

An important question to consider regarding the growing importance of aquaculture as a food source is: as quantity increases, does quality decrease? For instance, food contaminants, like mycotoxins put consumer health in danger and could result in profit loss in the global market.

Mycotoxins are a harmful group of toxic metabolites. They are widespread and many instances of negative impacts from exposure to them have been noted in animals, including humans.

Research reveals that mycotoxins are present in fish feed, which can leave a residue in fish that is sold to consumers.  Mycotoxins are found globally, however, some studies show that different regions yield a higher and more widespread presence of mycotoxin contamination than other regions. Table 1 in the original article summarizes the results of a study that measured various mycotoxins in fish feed in 2010 and 2013 from 11 regions globally. Their results revealed a wide spread occurrence of mycotoxins globally in both years and that they were particularly prevalent in developing countries.

The problems with contamination begin when animal feed is inflicted with fungi (figure 2). Many types of fungi produce various harmful mycotoxins. The fungi can appear during growth, harvest, and/or storage.   Optimal growth conditions are related to temperature, humidity, rainfall, how easily they are able to grow, the type of soil, and nutrient availability. The mycotoxins  produced depends on the fungus type that they are synthesized from.  For these reasons the geographical distribution of the different types of mycotoxins varies.

Mycotoxins are synthesized from fungi, like that which is growing on these peaches (source: https://en.wikipedia.org/wiki/Mold_health_issues)

Figure 2: Mycotoxins are synthesized from fungi, like that which is growing on these peaches (source: https://en.wikipedia.org/wiki/Mold_health_issues)

Available data and evidence support the standardization for fish feed quality is important to ensure that healthy feed makes healthy fish to feed humans that will hopefully stay healthy too. If the fish feed toxin can be limited, especially in developing countries, it ensures more food to feed future generations, and it ensures the food is not harmful to comsumer health.

Risk of mycotoxin exposure comes with consumption of contaminated meat and fish.   In humans, mycotoxins have life-threatening health impacts including cancer, kidney disease, liver disease, immune system suppression, carcinogenicity, and neurotoxicity. Unfortunately, it is extremely difficult to trace health impacts of mycotoxins back to their original source. This will likely remain the case as long as there are insufficient laboratory testing methods and criteria on how to diagnose mycotoxin derived illnesses.

In addition to the potential health threats, mycotoxins can also cause a loss in product because the fish farmed are not as healthy. They may show symptoms like being under weight, have inefficient immune systems, internal lesions, and death. The effects of mycotoxins on animals are related to factors including the length of exposure time, the species, the gender, and age of the animal exposed. Table 2 in the original article summarizes various experiments in which different species of fish were exposed to a toxin for varying lengths of time, and the resultant symptoms and effects observed in each species.   The type of toxin present is also an important factor in the symptoms observed. The most concerning forms of mycotoxin are aflaxtoxins (B1, B2, G1, G2, and M1) ochratoxin A, and those produced by a molds classified as Fusarium. Table 3 in the original article summarizes studies that targeted the toxic effect of various doses and exposure times to mycotoxins. The results of all of the studies support that mycotoxin science is dynamic.  To help understand their complex distribution and effects, regulatory guidelines for laboratory analysis need to be established.

Health and market protection are two drivers for the FDA, European Commission, and other regulatory committees (Figure 1 original article) setting limits for the amount of mycotoxins allowed in ingredients that are used in fish feed, the fish feed itself, and the fish sold to consumers (summarized in Table 5 or the original article). Regardless of the regulations and the efforts of many nations to monitor the presence of mycotoxins, safety standards pertaining to an acceptable level of mycotoxins are difficult to constrain because mycotoxins are so complex.  Setting umbrella regulations for mycotoxins is challenging because each mycotoxin has a unique toxicity, the combination of multiple toxins will have varying effects, the type of feed effects what mycotoxins are present and at what levels, and the accumulation of mycotoxin varies between organs, for example, not much residue was found in fish muscle when compared with fish liver (Table 4 original article).  There are also limiting factors such as the availability of information about mycotoxin occurrence, knowledge about how the toxins are distributed, the various effects they can have, the availability of detection methods, and the demands of the global market and related politics.  All of these limitations together hinder the ability to completely legislate the acceptable level of mycotoxins derived from aquaculture.

Even if regulations are set and work perfectly to eliminate the health risks to consumers, there still exists a major caveat. The problem is that the regulations that are set are in regards to the product (food sold to consumers) and not the process of production, which includes the initial planting and growth, harvesting and storage, detoxification, transport, additional storage and processing, and so fourth. By not fixing the source of the problem (the processing) the issue of mycotoxins can never truly be resolved; toxic product will continue to be produced, but as a loss because it cannot be circulated into the market.  Unfortunately that means that even if regulations result in reducing the negative impacts on human health, there still may be economic losses felt by every link in the production and distribution chains.

The take home message is that in addition to safety regulations related to the product sold,  guidelines for the production and storage of animal feed should be established to truly minimize the risk of mycotoxin contamination.  With both measures, and a lot more science, the potential exists to protect the quality and health of crops, fish, consumers (humans), and the aquaculture market as the demand for quantity continues to increase.

Anne M. Hartwell
Hello, welcome to Oceanbites! My name is Annie, I’m an earth scientist (geology and oceanography). My favorite job as a scientist is working in the laboratory and the field because I love interacting with my research!


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