Dr. Dušan Palić
A look into the future of the aquafeed industry

Explore the challenges faced by the aquafeed sector in mycotoxin prevention and control with Dr. Dušan Palić (Chair at Ludwig-Maximilians-University Munich).

Prof. Dušan Palić is a veterinarian with a Master of Veterinary Sciences in Veterinary Preventive Medicine – Immunology from the University of Belgrade. He completed his Ph.D. in Immunobiology and Fisheries Biology with Honors at Iowa State University and is a Founding Diplomate (European Veterinary Specialist) of the European College for Aquatic Animal Health. He is the Chair Holder for Fish Diseases and Fisheries Biology at the Faculty of Veterinary Medicine of Ludwig-Maximilians-Universität München.

He is also the Director of the LMU Center for Excellence in Aquatic Veterinary Medicine, Biosecurity and Education; Executive Director of the International Aquatic Veterinary Biosecurity Consortium, Former Vice-President of the European College for Aquatic Animal Health and Distinguished Fellow and Former President of the World Aquatic Veterinary Medical Association.

Prof. Palić, you have dedicated your professional career to different lines of research in Aquatic Animal Health. What spiked your interest in this exciting field and what would you advise to new researchers who would like to follow in your footsteps?

Dear Mycotoxinsite readers, I first want to thank you for this opportunity to share some of our work in the area of mycotoxin research.

A “family legend” that is being re-told now to my children by my parents says that, when I was about two years old, I tried to catch some of the fishes in my father’s aquarium. After I pushed away the cover, I dove in head first and my father pulled me out last minute.

Since that event, some say that my fascination with underwater life is likely a consequence of staying underwater for too long (not excluding a possibility of hypoxic brain damage).

A more realistic reason is that I had excellent role models thanks to the Veterinary history of my family, as both my grandfather and my father were Professors at the Faculty of Veterinary Medicine, University of Belgrade.

I was fascinated by aquatic life since an early age, so one way or another (or both), Aquatic Veterinary Medicine was a path I choose to follow to this day.

The single most important piece of advice I can give to anyone who would like to pursue a career in this field (or any area really) would be that you have to love what you do, otherwise, it makes no sense to spend countless hours working on solving problems that ultimately do not make you feel as if you fulfilled your purpose on Earth.

That being said, if you are really, really into becoming a Fish Veterinarian, you are in for a treat. All it takes is to embrace it as your life vocation, not a job.

The demand for animal protein is predicted to increase substantially in the upcoming years. However, fish and other aquatic species are not usually the first to come to mind when thinking about animal-derived protein. Could you give us an idea of the actual scope and importance of the aquaculture industry as a means to feed the world?

The most recent estimates about the global animal protein needs are from the pre-COVID-19 period in 2019/20.

However, the trend is clear: aquatic animals (capture fisheries and aquaculture taken together) currently contribute about 40% to global animal protein production, up from about 25% in the early 2000s.

Almost all of this increase comes exclusively from aquaculture. Further estimates indicate that in the near future, around 2030, the contribution of seafood to satisfy global demands will reach half of the produced animal protein, with aquaculture constituting about two-thirds of that amount.

To meet these expectations, it is critical to maintain the aquaculture industry growth rate to avoid the potential formation of a supply-demand gap.

This gap could be as big as 50 million tons and could leave many of the poorest and neediest without access to one of the best quality protein sources in the world.

One of the major, if not the biggest, constraints to keeping the aquaculture growth rate high enough are disease problems, many due to inadequate water quality and nutrition of the fish in production.

In this context, high-quality feed and feed additives may be used to improve the overall health status of aquatic animals and support aquaculture growth.

Given the importance of the aquaculture industry, the aquafeed industry is expected to grow considerably. What are the main challenges faced by this industry in terms of raw materials and feed safety?

The main challenges in the aquafeed industry are related to the sustainability of aquaculture growth while maintaining high-quality standards at the same time.

We simply need to find a way to minimize the use of fish to feed the fish. In other words, the reduction of fishmeal and fish oil in aquaculture is the way of the future.

In this context, various plant-based protein and oil sources are currently in development to replace fish meal/oil and make aquaculture even more sustainable industry.

However, it is not always easy, as it also depends on the fish species and their ability to digest and utilize these new feed ingredients.

Additionally, there is increasing competition for high-quality plant-based raw materials used in feeding terrestrial vs. aquatic animals.

With an increase in demand, the cost of raw materials becomes too high and some companies or farmers turn to lower quality sources to maintain the competitiveness of their food on the market.

Another issue that frequently escapes the “spotlight” is the use of local/generic feed raw materials to supplement fish feed, particularly in small-scale and rural aquaculture in developing countries.

Not all fish farmers can afford to purchase higher quality (or at least standardized quality) feed from aquafeed companies. Therefore, they resort to the local suppliers of raw materials such as corn, soybeans, and others.

Unfortunately, these crops are frequently produced, stored, and sold in less-than-optimal conditions, causing possible entries of contaminants in the food chain, causing some food safety concerns such as mycotoxins.

Mycotoxin occurrence in animal feed is a major concern for the industry. In the case of the aquafeed industry, which are the main ingredients and mycotoxins to look out for?

As mentioned above, with the effort to minimize the use of marine fish-based oils and protein, multiple alternatives are being considered, for example other (even aquaculture) fish offal and slaughter or farming by-products, including animal manure.

However, the focus is mainly on plant-based sources of protein and oil such as corn, soybeans, various post-processing by-products such as oil-pressed cakes and meals, bioethanol by-products, silage (from plants or animals), and many more.

Now, in most circumstances, mycotoxins occur in many, if not all, feed raw materials of plant origin if the environmental conditions are favorable. To some extent, the presence of mycotoxin-producing fungi is less frequent in feed ingredients coming from animals (marine fishmeal and fish oil), but it is not unheard of.

Therefore, unless tested for presence/ absence and determined that mycotoxins are below the detection limit, either the manufacturer or the producer cannot be sure if the feed they are using either as raw materials for pellets or as a direct supplement in the aquaculture, is mycotoxin free.

Major groups of mycotoxins can all be found in different feedstuff, individually or, more often, simultaneously. Frequently, multi-mycotoxin contamination can sometimes go undetected if not tested, especially if one or more mycotoxins are present but are individually below legal limits.

Such multiple contaminations are especially important, as we know very little about the synergistic effects of different mycotoxins on aquatic animal health and other production parameters.

While aflatoxins in recent decades have been the “most famous” of all the mycotoxins, we should keep in mind that there are over a hundred different mycotoxins and many of them are known to cause human health problems for centuries (e.g., ergotism), and still are causing animal health problems.

In aquaculture, problems have been reported with all the major mycotoxin classes, not only with aflatoxins.

As a researcher, you have conducted many studies on mycotoxins and their effects on aquatic species. Do these effects differ much from those found in other farm animals? Is there a higher risk of mycotoxins exposure in humans through the consumption of fish and other aquatic species that have ingested these toxins?

The health status of farmed animals exposed to high concentrations of individual mycotoxins is endangered due to the acute or chronic toxic effects dependent on the mycotoxin but also animal species.

Therefore, it is somewhat difficult to generalize and studies show that, for example, salmonids such as rainbow trout are more susceptible to much lower doses of aflatoxin compared to channel catfish that show greater resilience to quite high concentrations.

Overall, the toxic effects of different mycotoxin groups are similar in terrestrial and aquatic animals. For example, aflatoxins cause liver pathology, and ochratoxins are toxic for kidneys.

However, stress caused by the presence of diverse mycotoxins can also cause general immunosuppression and opens the door for further health problems, including increased susceptibility to infectious diseases.

The risk associated with the consumption of aquatic animals that have been fed mycotoxin-contaminated feed is still not well understood.

Some studies suggest that there is a relatively low risk of bioaccumulation of aflatoxins in the muscle tissue of fish and shrimp, while there is also some evidence that AFB1 residues are present in fish muscle in relevant concentrations and cause human health problems.

Similar discrepancies in OTA studies have also been reported, pointing out that there is still quite a lot that we don’t know about the metabolism and accumulation of mycotoxins in aquatic animals.

Our knowledge about the bioaccumulation and biotransformation of mycotoxins in aquatic animals is almost non-existing in situations where multiple mycotoxins at low (below regulatory threshold) concentrations are used for prolonged times.

In your opinion, what are the key points that are essential to minimize mycotoxin exposure in aquatic species and carryover through the food chain?

The ways to minimize mycotoxin exposure are actually simple to list, but some of them can be very difficult to implement.

I would divide this into three main options and I would strongly suggest that all three are used simultaneously in order to reduce the risk of mycotoxin exposure and carryover.

1. SURVEILLANCE OF RAW MATERIALS

The first point would be consistent surveillance of the presence of mycotoxins by testing the feed raw materials used in the production of commercial feed or used directly as food in aquaculture.

With today’s globalization of trade and the use of feed raw materials from all over the world, it is crucial to reject (or not use) contaminated ingredients when preparing the commercial feed.

Surveillance has usually routinely been done in larger companies, but it remains a problem for small feed mills and direct use of contaminated feeds in farms.

2. MYCOTOXIN BINDERS

The second, and probably easiest to implement, the point is to use feed ingredients mixed with, or commercial feed that has been supplemented with, some type of mycotoxin binder.

This approach probably achieves the maximum protection with a minimum investment, as most binders interact with:

  • Mycotoxins that were not detected (or not tested for).
  • Mycotoxins that were detected, but in concentrations under the rejection limit

Choice of mycotoxin binders should be based on:

  • Binding capacity, range, and strength
  • Range of mycotoxins that can be adsorbed

3. SURVEILLANCE OF PRODUCTS FOR HUMAN CONSUMPTION

Finally, and usually associated with a regulatory human food safety aspect, the surveillance and testing of aquaculture products intended for human consumption for the presence of mycotoxins is of high importance.

This point is especially relevant for producers that do not use feed with binders and, therefore, are at a higher risk of introducing mycotoxins through their feeding practices.

The inclusion of mycotoxin binders in feed has proven to be a very effective way to prevent the negative effects of these deleterious toxins when they are already present. What recommendations can you give us in this regard and which are the main errors that may reduce their efficacy?

Yes, to elaborate on the answer to the previous question, it is of great importance that the mycotoxin binders have a strong binding capacity and are able to bind multiple mycotoxins that are frequently present in feed raw materials.

The wide diversity of mycotoxins and the variability of their chemical composition make it necessary to use binders that can effectively interact with polar and non-polar mycotoxins.

Many mycotoxin binders can be used and the choice does not only depend on their quality, as their price and suitability must also be considered to be incorporated or added to the commercial food production chain.

In aquaculture, commercial feed is frequently produced via extrusion processes, something that should be taken into account to ensure that the mycotoxin binder is suitable for extrusion.

Many mycotoxins only react with the binder when the food pellet is exposed to water and mycotoxins get in contact with the binder in a water environment. This is particularly interesting for aquaculture as feeding is performed in the water, so this reaction happens even before the feed reaches the fish stomach and in addition prevents the release of mycotoxin in the environment.

Where do you think the aquafeed industry will go from here in terms of feed safety and mycotoxin control?

The major commercial suppliers of aquafeed already have good systems in place to minimize the risk of the introduction of mycotoxin contaminated raw ingredients.

Many of them are also already using mycotoxin binders in their products to reduce risks even further. However, the surveillance and rejection approach are frequently incompatible for mid to small-scale aquatic feed producers or local feed mills producing a limited quantity of fish feed from raw materials of uncertain quality.

In those cases, adding a reliable mycotoxin binder that covers a broad range of the possible contaminants is crucial to reduce the risk of transferring mycotoxins into the animal and possibly further up the food chain.

What would be your take-home message for our readers from the aquaculture and aquafeed industries?

The demand for raw feed materials is growing and the pressure to use lower quality feedstuff is increasing. This has led to an increase in the risk of introducing contaminants into aquaculture production and consumption of aquatic animals.

In order to protect the health of your animals and of the people consuming them, it is very important to minimize the risk of mycotoxin toxicity. The most effective and simple way to achieve this is to use broad-spectrum mycotoxin binders either in commercial feed or as additive to locally raised and produced feedstuff.

Micotoxicosis prevention
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