World Aquaculture Magazine - June 2021

58 JUNE 2021 • WORLD AQUACULTURE • WWW.WA S .ORG and Penicillium species produce immunotoxic mycotoxins such as aflatoxin and ochratoxin A that can cause poor fish performance (Kumar et al . 2013, Oliveira and Vasconcelos 2020). Mycotoxin contamination is a common occurrence in grain-containing feeds (Anater et al . 2016). Moreover, there has been a high incidence of aflatoxin contamination in fish feeds from the Middle East, Africa and Asia. Some clinical symptoms of aflatoxin contamination are liver and brain damage, eye cataracts and skin lesions (El-Sayed and Khalil 2009). Ochratoxin A contamination can lead to necrosis of liver and kidney tubule cells (Manning 2005). Co-occurrence of aflatoxin and ochratoxin A in pelleted feeds is also possible (Barbosa et al . 2013). The presence of these two mycotoxins can impose a health risk to consumers as well as to farmed fish. There is also an increasing concern for prevalence of emerging mycotoxins in Fusarium (Fraeyman et al . 2017). Fusarium species may be present in agricultural crops used as rawmaterials for fish feeds (Ivic et al . 2009). Some Fusarium Species and Their Occurrence in Aquafeeds Fusariumverticillioides This species is formerly known as Fusariummoniliforme . It usually contaminates grains, especially corn (Blacutt et al . 2018) and is a plant pathogen commonly found in soil. It is described as a facultative endophytic fungus with purple or pink mycelia that can infect plants systemically through seeds or wounds caused by external factors, such as insect herbivory (Pascual et al. 2016). This fungus is a contaminant of several types of feeds. Fusarium culmorum and F. verticillioides were isolated and identified through DNA barcoding from a jellified pellet containing F ish health needs to be monitored for successful aquaculture. Proper fish growth and development is an important key for greater gains and can be attained by providing fish feed with balanced nutrients, acceptable water quality and an innovative aquaculture system. Ubiquitous microorganisms can directly cause poor fish growth. The occurrence of diseases can cause major losses, costing multi-billion US dollars yearly (Subasinghe et al . 2001). The sources of microbial communities are from feed preparation and storage, product transport and culture water (Oliveira and Vasconcelos 2020, Gonçalves et al . 2017). Most bacterial contaminations are prevented by regulated use of antibiotics (Defoirdt et al . 2011, Rico et al . 2013, Song et al . 2016). Nonetheless, bacterial infections are not the only culprits of disease outbreaks. The presence of fungi, especially in feeds, can also pose a threat to aquaculture. Fungal growth in fish and crustacean feeds is influenced by factors such as feed composition and preparation method. The use of plant-based ingredients to replace fishmeal increases the risk of fungal contamination (Pietsch 2020, Gonçalves 2017). Certain molds can produce toxic compounds called mycotoxins. Mycotoxins are described as low-weight secondary metabolites of filamentous fungi (Leslie and Summerell 2006) that can thrive in agricultural crops such as nuts, grains, fruits, oils and vegetables (Fraeyman et al . 2017). Studies on terrestrial livestock animals have shown that exposure to certain levels of mycotoxin can lead to lower feed intake, feed efficiency, weight gain and reproductive capability (Tolosa et al . 2014). Nonetheless, mycotoxin screening is still not a common practice in aquaculture. Some of the well-known fungal genera that can produce mycotoxins are Aspergillus , Penicillium and Fusarium. Aspergillus The Potential Threat of Fusarium Mycotoxins in Aquaculture Feeds Tzodoq ObreroMagbanua and Janice Alano Ragaza Fusarium sp. is the greenish mold surrounding the border of a piece of potato dextrose agar in this slide culture. This process is done to visualize the fungus under the microscope (Photo: J. Escobin). Rice, a staple food crop in Asia, may be contaminated with mycotoxins, albeit at much lower levels than in wheat and corn (Photo: J.A. Ragaza).