Potential effects of deoxynivalenol (DON) on the health of farm raised fish
Aquaculture, in contrast with capture fisheries, has remained stable over the last few decades. The industry continues to grow and contribute to the increasing food supply for human consumption, reaching worldwide production of 80 million metric tons (Mt) in 2016. To sustain its growth, the aquaculture industry is highly dependent on commercial feed sources. The inclusion rate of traditionally used finite and expensive marine protein and fat sources from wild-caught fish (i.e., fishmeal and fish oil) in the diets of farm-raised fish species will continue to decline, and the industry has already shifted to crop-based raw materials to meet the rising demand for aquafeeds.
Fish require several carefully chosen raw materials to provide them with a healthy diet, but fish-based proteins are not essential. The industry has recognized this, and there are now many fish feeds with 0% fish-based protein ingredients and an industry average (FIFO Factor). Plant-based feed ingredients increasingly replace marine-based components, and therefore, an enhanced level of understanding of the nutritional quality of raw materials derived from plant sources is becoming increasingly crucial for aquafeeds. Moreover, the higher inclusion of less-expensive plant sources may introduce a series of anti-nutritional factors (e.g., protease inhibitors, phytates, saponins, glucosinolates, tannins, non-starch polysaccharides) and/or increase the occurrence of mycotoxins in fish feed; factors that may affect the quality and safety of aquafeeds.
Mycotoxins in aquaculture feed
Mycotoxins are fungi that can grow on crops during growth, harvest, processing or storage. The development of these fungi is climate-dependent and most commonly seen in tropical regions. In these climates, the fungi produce chemical compounds known as mycotoxins and can have a greater impact on animal health.
Fish farming is a diverse industry, and each aquaculture species will have different sensitivities to the impacts of mycotoxins. These can cause a reduction in performance — reduced growth and increased feed conversion ratio (FCR) — and increased disease susceptibility and mortality rates. As these issues can be attributed to other concerns, the risk can often be overlooked and underestimated in aquaculture.
Mycotoxins are mainly detected in plant-based feedstuffs, readily present in corn, wheat and soybean meal. Increasingly, the occurrence of mycotoxins has been reported in aquafeeds. There are over 50 different types of mycotoxins, but the most commonly known and most prevalent is deoxynivalenol (DON).
Effects of deoxynivalenol on the health and growth of farmed fish species
Accumulation of DON in fish can be harmful and impact their performance. In terms of occurrence and toxicity, DON has been characterized as the most high-risk mycotoxin in aquafeeds. Its effects include:
1. Ribotoxic stress response: DON binds to ribosomes, inducing a “ribotoxic stress response” that activates mitogen-activated protein kinases (MAPKs).
2. Oxidative stress: DON causes oxidative stress in cells by damaging mitochondria function, either through the excessive release of free radicals — including reactive oxygen species (ROS), which induce lipid peroxidation — or by decreasing the activity of antioxidant enzymes.
3. Impacting epithelial cells in the digestive tract: Predominantly, rapidly proliferating cells with a high protein turnover, such as immune cells, hepatocytes and epithelial cells of the digestive tract, are affected by DON.
4. Reduced growth rate: In Atlantic salmon diets, 3.7 mg/kg of DON resulted in a 20% reduction in feed intake, an 18% increase in FCR and a 31% reduction in specific growth rate. In white shrimp, DON levels of 0.5 and 1.0 ppm in the diet significantly reduced body weight and growth rate, while FCR and survival were not affected.
5. Decreased immune system response: Mycotoxins impair optimum animal performance by affecting intestinal, organ and immune systems. These, in turn, negatively impact overall performance and profitability.
6. Reduced feed intake: A study conducted by Woodward et al. (1983) showed that rainbow trout had a sharp taste acuity for DON. Their feed intake declined as the concentration of DON increased from 1–13 ppm of the diet, resulting in reduced growth and feed efficiency
The impacts will vary on many factors, including the quantity, feeding level, duration of exposure and aquatic species. A recent meta-analysis completed by Koletsi et al. (2021) highlights the risk of DON on feed intake and growth performance. In parallel, data was collected to quantify the risk of exposure in fish. The extent to which DON affects feed intake and growth performance was evaluated by employing a meta-analytical approach.
Having completed a full meta-analysis of the current research and trial data available for the aquaculture species, Koletsi et al. concluded that the current recommendation for the limit of DON in fish diets is too high and needs to be reviewed in order to protect the welfare of fish and maintain an economic advantage.
Preventing mycotoxins in aquaculture
Maintaining a good management system will help to control the mycotoxin risk. However, some mycotoxins remain stable, even after high-temperature extrusion processing. For this reason, additional steps should be taken to mitigate the risk. Alltech mycotoxin management tools, such as Alltech 37+® and Alltech® RAPIREAD, help farmers and feed producers identify their total mycotoxin risk (REQ). Evaluating risks associated with mycotoxins on animal performance and financial losses can be more rapid than ever before. Additionally, to further manage mycotoxin risk and understand what you can do for your business, you can visit knowmycotoxins.com.
References available on request.