Dr. Rui Alexandre Gonçalves
Aquaculture and Mycotoxin Expert
Aquaculture Business Developer – Lucta S.A.
Innovation Division – Feed Additives
UAB Research Park, Bellaterra, Barcelona, Spain
The awareness of mycotoxin-related issues in the aquaculture industry has been increasing, accentuated by the replacement of marine ingredients (Gonçalves et al., 2018; Tacon et al., 2011).
|Traditionally, the use of minor amounts of plant feedstuffs led to a general perception that mycotoxins were not a relevant issue in aquaculture and that the majority of mycotoxin-related issues would only arise due to poor storage conditions, i.e., aflatoxin contamination, but this is not entirely true.|
Mycotoxins are secondary metabolites produced by some molds (Hussein and Brasel, 2001). They are commonly reported to appear in agricultural commodities (pre-and/ or post-harvest), including finished feeds.
Chemically, mycotoxins have low molecular weight, displaying a wide range of structures (Mallmann and Dilkin, 2007). This variability is responsible for the diverse biological effects produced by mycotoxins.
|Despite being identified as categorically undesirable for most animal species, the occurrence of mycotoxins, at least in field conditions, is not completely preventable even when using good manufacturing practices.|
As mycotoxins are mainly found in agricultural commodities, the tendency to replace animal-derived proteins, such as fish meal, with plant protein sources has increased the risk of mycotoxin contamination in aquaculture feeds.
Generally, plant-based meals are known for their natural profile of anti-nutritional factors (ANF’s), such as cyanogens, saponins, tannins, etc., that are harmful to fish and shrimp (Krogdahl et al., 2010).
⇰ Although there are processes that aid in the removal or inactivation of many of these ANF’s, the same does not apply to mycotoxins, as they are highly stable when subjected to processing conditions (e.g., high temperature and pressure) (Cheli et al., 2013).
Not all plant meals are the same!
The difficulty in understanding the risk of mycotoxin contamination in aquaculture finished feeds is related to the diversity of aquaculture species. For most species, the selection of plant meals depends on a combination of factors (Davis y Sookying, 2009; Gatlin et al., 2007; Krogdahl et al., 2010):
- ⇰ Local market availability.
- ⇰ Cost.
- ⇰ The protein meal’s nutritional profile (anti-nutritional factor content and levels).
However, depending on the species and production region, evaluating mycotoxin contamination may not be a common practice in the aquaculture industry, so it becomes difficult to understand the contamination risk of certain plant commodities, especially the ones used locally.
Moreover, climate change and world commodities trade also contribute to the difficulty in predicting the risk of mycotoxin contamination in aquaculture finished feeds.
When plant meals get too expensive
The increasing cost and sustainability concerns on the use of marine ingredients for aquaculture feeds have encouraged the use of plant proteins. However, recently, the cost of plant-based raw materials has begun to rise, partly due to the increased demand for human and livestock species consumption and production challenges associated with the sustainability of certain plant commodities.
⇰ As a consequence, the volume and quality of affordable plant materials available for animal feed has fallen.
Aquaculture feed manufacturers are now faced with either increasing the price of aquaculture feeds or trying to use alternative sources of plant meals.
⇰ Economic pressures can lead to the use of lower quality raw materials which may increase the risk of contamination with one or more mycotoxins.
Alternatively, by-products and processed ingredients could be used but they are known to have increased levels of mycotoxins since most of the mycotoxins are not destroyed during commodity or feed processing (Gonçalves et al., 2017). These mycotoxins can also be redistributed and concentrated in certain milling fractions.
|The lack of legislation regarding mycotoxin contamination for aquaculture species also leaves some room for aquafeed manufacturers to use feedstuffs that have been rejected by the livestock sector because of mycotoxin contamination and stricter regulation.|
The contamination of aquafeeds and plant-based feedstuffs with mycotoxins is, in general, often neglected. Currently, there is a growing knowledge regarding mycotoxin contamination in aquafeeds and ingredients destined to be used in fish and shrimp feeds (Gonçalves et al., 2016; Gonçalves et al., 2017).
However, several gaps on how to improve and address mycotoxin risk management in aquaculture still remain.
Awareness of mycotoxin-related issues in the aquaculture industry
The awareness of mycotoxin-related issues in the industry has grown as feed manufacturers and producers realize the importance of mycotoxins and their potential to impact animal production. However, the idea that the majority of mycotoxin-related issues are a result of poor on-farm storage conditions leading to aflatoxin contamination is still deeply entrenched across the aquaculture industry.
While it remains true that poor storage conditions can promote the growth of Aspergillus sp. and Penicillium sp., ultimately leading to the production of aflatoxins and ochratoxin A, the reality is that most of the mycotoxins found in finished feeds come from the raw materials used to produce them.
|This was shown by Gonçalves et al., (2017), who reported that in Asian samples, soybean meal, wheat, wheat bran, corn, corn gluten meal, rapeseed/canola meal, and rice bran were mainly contaminated with Fusarium (ZEN, DON and FB).|
⇰ The only exception was cottonseed meal, which was mainly contaminated with AF and Fusarium toxins (ZEN and DON) in considerable amounts.
Finished feed samples were also mainly contaminated with Fusarium mycotoxins, reflecting the use of plant meals.
|Results shown by Gonçalves et al., (2017) confirm that mycotoxin contamination found in finished feeds is mostly related to the plant-based raw materials used in their formulation, since Fusarium fungi are generally found in field samples rather than in storage samples.|
The mycotoxin risk of less typical commodities should not be ignored!
As mentioned before, mycotoxins are mainly found in agricultural commodities. However, other commodities may also be contaminated with mycotoxins and should not be ignored.
Theoretically, under suitable conditions, any commodity may be a good substrate for fungal growth and mycotoxin production.
In reality, little attention is given to other commodities besides agricultural commodities.
However, in the case of aquaculture, aquatic by-products (both from fisheries and aquaculture) represent a significant inclusion level in aquafeed formulations. Therefore, their possible contribution to mycotoxin contamination should be also investigated.
For example, shrimp head meal is an important by-product of the shrimp industry.
Shrimp head constitutes 34 to 45% of the whole shrimp, being shrimp head meal (SHM) an important by-product of the shrimp industry. A possible SHM contamination with mycotoxins (at storage or by bio-accumulation) could represent a big constraint for the industry.
⇰ Shrimp meal can be manufactured by drying the material directly under the sun or in an oven (Hertrampf y Piedad-Pascual, 2000).
Shrimp meal can be manufactured by drying the material directly under the sun or in an oven (Hertrampf and Piedad-Pascual, 2000).
Considering that production is normally done in small lots of sun-dried fish under different conditions, a certain variation in the quality of the commodity can be expected.
|While not being a typical product to analyze for the presence of mycotoxins, it is known that their presence is possible
⇰ This is especially true in the case of mycotoxins such as AF and OTA, as they are produced by Aspergillus sp. and Penicillium sp. species that proliferate under inadequate storage conditions.
While it is easy to understand the possible contamination of aquatic by-products with AF and OTA, as they are storage mycotoxins, it is harder to fully explain the presence of less common toxins produced by Fusarium molds that are generally associated with field conditions rather than storage.
⇰ However, Fegan and Spring (2007) reported several marine-derived samples from fishmeal to shrimp meal were contaminated with mycotoxins produced by Fusarium sp. (N=5, origin Asia; T-2= 60.186 ppb and ZEA= 72.036 ppb). Later on, Gonçalves et al. (2017) sourced samples of dried fish and shrimp head meal (SHM) contaminated with fumonisins (N=2; Origin: Thailand; FB1 + FB2; dried fish= 64 ppb; SHM= 24 ppb).
In reality, is difficult to fully understand the origin of Fusarium mycotoxins in marine-derived byproducts. Some Fusarium strains, namely F. oxysporum and F. solani, are known and well described as opportunistic pathogens for fish and shrimp (Hatai et al., 1986; Lightner, 1996; Ostland et al., 1987; Souheil et al., 1999).
The capacity of F. oxysporum or F. solani to produce toxins is unknown, but the possibility of having aquatic Fusarium strains producing these mycotoxins cannot be totally rejected and this hypothesis needs to be further investigated.
Another possibility for the presence of Fusarium toxins in these aquatic by-products may be due to their bioaccumulation and to the fact that they are not destroyed during processing.
However, the topic of mycotoxin bioaccumulation in aquaculture products is little documented ( (Gonçalves et al., 2020).
Some take-home messages
Despite the efforts to control fungal contamination, both in the field and in storage, extensive mycotoxin contamination has been reported in commodities and finished feeds. The type and prevalence of mycotoxin contamination depend on:
- ⇰ The type of substrate (plant meal type and finished feed characteristics).
- ⇰ The geographical area.
- ⇰ Seasonal and local weather conditions during critical plant growth stages or storage.
Besides agriculture commodities, the risk of mycotoxin contamination in other aquatic by-products should not be ignored. Despite being less characterized when compared to agricultural commodities, some scientific pieces of evidence point to these commodities as a possible source of mycotoxins.
Mycotoxins occurring in plant commodities and/or aquatic by-products are not destroyed during most processing operations.
On the contrary, processing affects the distribution of mycotoxins, concentrating them into fractions that are commonly used in animal feed (plant by-products; e.g., corn gluten meal, DDGS, etc.).
The fate of mycotoxins during cereal processing (sorting, cleaning, milling, and thermal processes) has been studied by several authors. However, their level in feedstuffs is variable and affected by several factors:
- ⇰ The type of mycotoxins.
- ⇰ The level and extent of fungal contamination.
- ⇰ The complexity of the cereal-processing technology
|It is recommended that aquafeed and aquaculture producers regularly monitor raw commodity feed ingredients and finished feeds for mycotoxin contamination, either through on-site rapid testing or through an external laboratory that may be equipped with more powerful detection equipment.
In cases where feed quality has been compromised by mycotoxins, the use of a mycotoxin deactivator is advised.