Book review: Mycotoxins in Aquaculture, published by Biomin
Authors: Rui Gonçalves and Michele Muccio; Edited by Annliese Müller
This is a beautifully produced book with both an extremely detailed Table of Contents at the front of the book and a detailed index at the back of the book. The care and attention that has obviously gone into both means it should be quick and easy for readers to look up any specific topic they are searching for.
The front of the book also features a highly useful list of acronyms and a list of figures and tables. The book is divided into seven major sections which focus on various aspects of mycotoxins that are of specific interest to those working in aquaculture.
In the introduction, the three authors: Rui A Gonçalves, Michele Muccio, and Editor Anneliese Müller make it clear that a central focus of the book is the current trend of replacing fishmeal with plant-based materials in fish feed and the potential impact of antinutrients such as mycotoxins found in plant matter.
Their concerns are supported by the number of studies recently published at conferences (many undertaken by Biomin), and highlight the need to be aware of this issue and the need for continuing research on the potential impact of mycotoxins on the aquaculture industry.
Section 01: Mycotoxins
The book opens with a definition of what mycotoxins are, and how they occur.
Mycotoxins are produced by fungi and can contaminate crops, either in the field or during storage, and consequently they occur in animal feed and animal products. The role of antinutrients, especially mycotoxins, is not fully understood; however, mycotoxins exert detrimental effects on human and animal and productivity.
Even though we cannot fully explain their function, mycotoxins are produced during different stages of food and feed production and pose a serious health risk globally.
A further complication is the fact that feedstuffs are often contaminated with more than one mycotoxin. Global trading in commodities adds yet more complexity as feedstuffs from different geographical regions, many containing different fungal species, makes co-contamination of mycotoxins even more likely. In a 2027 survey conducted by Biomin, 71 percent of samples were found to be co-contaminated by two or more mycotoxins.
This has a direct effect on aquaculture, since plant proteins are increasingly being used in aqua feed. Aflatoxins can be expressed in lactating animals. When animals ingest contaminated feed, mycotoxins are able to mask their toxic effects and can be transformed in the mammalian digestive track back into their parent mycotoxin.
has carried out a number of worldwide surveys to evaluate the occurrence of mycotoxins in feed and raw feed materials. In the chapter on mycotoxin interactions, the authors explain how feedstuffs are often contaminated with more than one form of mycotoxin; this further complicates matters as low-level interactions of mycotoxins can exacerbate the toxicological effect of the diet.
Because aflatoxins commonly occur in feedstuffs, feeds and milk products, these mycotoxins represent a serious threat to humans and animals. While ingestion of food is the most common vector of infection, the inhalation of contaminated grain dust is another route.
After ingestion, Afla is absorbed through the duodenum and is transported through the bloodstream to the liver, the major site of metabolism.
Because aflatoxins occur at a high rate in African plants and feedstuffs, they cause high rates of liver cancer in the human African population. A shocking statistic is that aflatoxins are more likely affect more people in Africa than common diseases like malaria and tuberculosis.
The other mycotoxins
The authors then discuss in detail some of the other major mycotoxins including: Tricothecenes, Ochratoxins, Fumonisins, Zearalenone, and ergot alkaloids (Ergots and sclerotia are hardened fungal tissues that replace plant structures. They are generated by the fungus to help it survive adverse environmental condition). Mycotoxins is an overarching term which refers to a diverse group of around 40 different toxins found on grains such as triticale, corn, wheat, barley, oats, millet, sorghum, rice and various grasses.
Following the overview on the major forms of mycotoxin, the book provides an overview on worldwide regulations for dealing with mycotoxin contamination with a focus on the EU and USA.
Having defined the threat posed by mycotoxins in the first section, the authors address the defense mechanisms of aquatic species. Immunity is defined as the resistance to diseases, particularly infectious diseases. The immune systems is comprised of all the cells, tissues and molecules that mediate this resistance.
As with mammals, the immune system of fish has developed over millions of years. Fish, living in a watery environment rich in pathogens and antigens, are constantly challenged by parasites, viruses and bacteria. This is particularly the case in aquaculture, where large numbers of fish are held in close proximity with each other, and the stress of crowding can suppress their immune systems.
Fish have both an innate and adaptive immunity. The innate immunity responds to pathogens that invade the tissues, while adaptive immunity is specific to the type of pathogen. The two systems work together in concert.
However, fish possess an element not found in mammals, the mucosal immune system, located in the gills and the gut. This constantly regenerated layer, which covers the skin, the gills and the gut, provides a physical barrier to the entrance of pathogens.
Immune cells kill pathogens in the bloodstream by first recognising microbes and then proceeding to phagocytise them. There are a variety of immune cells, such as neutrophils, macrophages, basophils, eosinophils, mast cells, ridley cells, and Natural Killer cells that recognise and phagocytise pathogens.
Adaptive immunity is able to develop memory, following repeated exposure to the same pathogen, which allows it a faster and more efficient response to infections. Fish have immune systems comprised of specialised organs that synthesise lymphocytes and the mucuosae also help protect fish and contain immunological tissues.
Effects of mycotoxins on the immune system of fish and invertebrates
After introducing the elements of the fish immune system. The chapter moves on to a discussion of the effects of mycotoxins on those immune systems. The tend of replacing fishmeal in feed with plant protein opens the possibility of mycotoxin contamination.
Although most research is limited to a small number of commercially farmed fish, mycotoxins are some of the most powerful carcinogens that can damage organs and even do damage at a cellular level.
After a review of fish immunity, next the authors look at the immune systems of invertebrates such as shrimp. Although shrimp lack an adaptive immune system, they have a series of effector mechanisms that can produce an immune response.
It is likely that mycotoxins will affect the health of shrimp by immunosuppression and interfering with nutrient uptake, thus interfering with the animal's ability to recover. Mycotoxins are antinutrients and given the increase in plant-based protein in shrimp feed, it is important to study their effects on the immune system of shrimp.
Section 03: Mycotoxins in aquaculture
Although most of research on the effects of mycotoxins have been on traditionally farmed terrestrial species, since the 1960s a number of studies have been undertaken on aquaculture species such as trout.
As the use of plant-based protein has increased, so has awareness of the presence of mycotoxins in aquafeed. Despite this, there are still not many validated studies of the clinical symptoms of mycotoxins-related diseases in fish and shrimp. Slow growth is one of the most frequently reported symptoms.
The authors of Mycotoxins in Aquaculture chose to print a comprehensive table within the pages of the book which provides an overview of the literature on the effects of aflatoxins, deoxynialenol, fumonisins, ochratoxins and zearalenone in aquaculture fish species. The table runs a full 15 pages.
The remainder of the chapter then focuses on the main mycotoxins impacting first farmed fish and then shrimp.
Section 04: Occurrence of mycotoxins in aquaculture feed
The fourth section begins by reiterating the need for the fish feed aquaculture industry to maintain sustainability and environmental responsibility by developing alternative proteins to fish meal and fish oil.
While many anti-nutrients can be removed by processing, this does not apply to mycotoxins, which can survive processing intact. Plant materials selected for inclusion in aquafeed will vary according to local availability, which is a further complicating factor as studies of these plants potential contamination with mycotoxins may not have been studied.
The authors then went on to identify the most common mycotoxin-contaminated plant raw materials, which include soybean meal, wheat and wheat brain, corn and gluten meal, rapeseed/canola meal, cottonseed meal, rice bran, and various other plant raw materials.
Aquaculture by-products, such as shrimp head meal which is a valuable feedstuff for aquaculture, is not typically analysed for the presence of mycotoxins. Similarly, in much of Asia, sun-dried fish is ground to producer fish meal. However, mycotoxin contamination is possible with both of these feedstuffs.
Mycotoxins are frequently found to contaminate compound feed, because of the mixture of raw materials. A study showed that 50 percent of squared samples collected from Europe contained more than one mycotoxin, while 84 percent of those samples obtained from Asia were likewise contaminated.
The conclusion was that, while some aquaculture feeds contained low levels of contamination, in other samples the contamination level was sufficient to pose a significant threat to aquaculture species.
Section 05: Sampling and analysing mycotoxin content in feeds
The authors found that visual inspection of feeds was unreliable and that therefore a proper analysis of samples is necessary. Even then, this is a complex task consisting of several distinct phases.
The authors then cover sample preparation, and the various analytical methods and tests required to identify the presence and variety of mycotoxins present in a sample.
Section 06: Fighting mycotoxins
Having defined the problem of mycotoxins and explained its presence in feed using plant protein and described methods of detection, the final chapter delves into methods of presenting mycotoxin contamination.
Because mycotoxins occur in the plant materials used in fish feed, prevention must begin in the farm field and continue through the storage of the material. This last chapter looks at the common causes of mycotoxins of growing plants, such as moisture and temperature, aeration, sanitation, pests and storage conditions in silos.
Next, it focuses on elimination of mycotoxins through a variety of strategies ranging from physical processes such as mechanical cleaning and sorting, through heat treatment and more aggressive chemical processes, to bentonite and organoclays.