AFLATOXICOSIS AND ITS IMPACT ON AQUACULTURE FEED QUALITY, FISH HEALTH AND FARM PROFITABILITY
The quality of aquaculture feed is one of the most decisive factors in the success of aquaculture. In addition to the quality of feed ingredients and their production, feed storage conditions also have an impact on feed quality, particularly in terms of adventitious toxins. Mycotoxins are frequent contaminants of food and feed, and are considered major threats to human and animal health. In this context, the effects of mycotoxins on aquatic animals were examined, with particular emphasis on aflatoxin B1 (AFB1), which is clearly present in aquatic feeds. Severe tissue damage, increased susceptibility to infectious diseases, immune system impairment and increasing unknown mortality risks are among the effects of mycotoxins on aquatic animals, and increasing unknown mortality risks are among the most frequent symptoms of aflatoxicosis in aquatic animals. Given the importance of these fungal toxins on the economic viability of aquaculture businesses, it is recommended that more knowledge be obtained on the safety levels of AFB1 in terms of fish health and end-product safety for human consumers.
Introduction
World aquaculture production is projected to increase by 62% (35 million tons) from 2010 to 2030, with over 90% of such growth occurring in lower middle-income countries (World Bank, 2013) . Aquaculture has recently transformed into a more sustainable and productive industry model, mainly due to cost feed formulation strategy and search for fishmeal alternatives in the last decade (Tacon and Metian, 2008 ; Nasopoulou and Zabetakis, 2012). Fish feed is an essential part of the aquaculture industry and significantly contributes to fish production costs and quality (Kjørsvik, et al., 1990). It plays a pivotal role in determining the success and profitability of fish farming. Ensuring high-quality feed is vital for optimizing fish health and growth. However, it has been reported that the feed is prone to being contaminated by fungal toxins (Hussain, et al., 2017 ; Magouz, et al., 2018). The risk of toxin occurrence in feeds increases at temperatures above 27°C, humidity above 62%, and feed moisture content above 14%. Inappropriate feed storage is a common predisposing factor for fungal and mold growth (Santacroce, et al., 2008) and poses severe health issues in terms of human health and animal production costs and health (Belhassen et al., 20015 ; Dirican, 2015). Contamination with mycotoxins might result in decreased nutritional values of ingredients and finished feed (Bennett et Klich, 2003). Mycotoxins might be responsible for hepatocellular and neurologic injuries, hypoimmunity, cancer, and even an increased mortality rate (Francis, et al., 2024). The toxic effects of mycotoxins depend not only on their dietary contents but also on the duration of toxin exposure and fish species, gender, and ontogenic stage (Pleadin et al., 2017). Although there have been some reports regarding decreasing toxin bioavailability using dietary additives, including yeast cell wall, clay minerals, and pro/post-biotics, mycotoxins are still among the main risks of reduced fish growth performance and immune competence (Hussain et al., 2017 ; Ellis et al., 2000 ; Peng et al., 2022). Moreover, the long-term ingestion of feeds with low levels of mycotoxins or acute exposure to high dietary contents might be a reason for the unexplained mortalities occasionally observed in fish farms (Raghavan et al., 2011 ; Li et al., 2024). While the effects of mycotoxins are relatively wellknown in most terrestrial farm animals, the outcomes of dietary mycotoxin contamination on aquaculture species have yet to be extensively studied. Therefore, the present review focused on the effect of mycotoxins, especially aflatoxin B1 (AFB1), on aquatic animals in terms of fish growth performance, digestive tract physiology, immune system functionality, and intestinal barrier integrity. Such understanding plays a crucial role in managing the adverse effects caused by mycotoxins and increasing social awareness regarding the presence of such toxins in aquafeed.
1.1 What is aflatoxicosis?
Aflatoxicosis is a disease caused by the ingestion of aflatoxins, secondary metabolites produced by fungi of the genus Aspergillus, notably Aspergillus flavus and Aspergillus parasiticus. These toxins are often present in animal feed, including fish feed, and can have devastating effects on fish health and, by extension, on human food safety.
2. Contamination mechanisms
2.1. Sources of contamination
Aflatoxins are mainly found in food ingredients such as seeds, cereals and by-products. Environmental conditions, such as high temperatures and humidity, favor fungal growth and, consequently, mycotoxin production.
2.2 Storage conditions
Inappropriate food storage, particularly at temperatures above 27°C and relative humidity above 62%, increases the risk of mycotoxin contamination. Food management practices must therefore be rigorous to prevent contamination.
3. Effects of Aflatoxins on fish
3.1 Impact on health
The effects of aflatoxins on fish include :
– Tissue damage: AFB1 causes damage to the liver, kidneys and other vital organs, leading to metabolic dysfunction.
– Immune system compromise: Fish exposed to high levels of AFB1 show reduced immunity, making them more vulnerable to infection.
– Growth disruption: Prolonged exposure to AFB1 can lead to a significant reduction in fish growth and survival.
3.2. Clinical symptoms
Clinical symptoms of aflatoxicosis in fish include :
– Pallor of the gills: Indicates hypoxia or physiological stress.
– Abnormal behavior: Fish may become apathetic or show signs of agitation.
– Altered blood parameters: analyses often show a reduction in red blood cells and abnormalities in liver enzymes.
4. Sensitivity factors
4.1. Species variability
Sensitivity to aflatoxins varies considerably between fish species. Some species, such as rainbow trout, show increased sensitivity, while others, such as tilapia, may have a higher metabolic capacity to detoxify aflatoxins.
4.2 Environmental factors
Environmental factors such as water temperature, feed quality and stocking density stress can influence the susceptibility of fish to the harmful effects of mycotoxins.
5. Risk management recommendations
5.1. Monitoring and control
It is essential to establish safe limits for aflatoxins in fish feed. Regular monitoring programs should be set up to detect the presence of mycotoxins.
5.2. Education and awareness
Aquaculture producers must be trained in best feed management practices to reduce the risk of mycotoxin contamination. This includes appropriate storage methods and high-quality feed formulation.
5.3. Future research
Further research is needed to better understand safe levels of AFB1 and their long-term effects on fish health and human food safety. The development of rapid and effective methods for detecting mycotoxins in food is also crucial.
6. Conclusion
Aflatoxicosis represents a major challenge for the aquaculture industry, affecting both fish health and farm profitability. Effective mycotoxin risk management is essential to ensure the sustainability of aquaculture. By setting safety standards and raising awareness, the impact of aflatoxins on fish health and food safety can be reduced. As the mycotoxin content of food (feed) varies greatly from place to place, close collaboration between scientists and legislative authorities is required regarding sampling methods/frequencies, processing and/or analysis. In addition, it is necessary to develop rapid and practical methods for detecting (multi)mycotoxin contamination.
