World Aquaculture Magazine - June 2021

WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2021 59 Fusarium sp. is a filamentous fungus. The hyphal network functions for its vegetative growth. This image is taken under a microscope with 400x magnification, featuring unstained Fusarium sp (Photo: J. Escobin). It can cause contamination in finished feeds or feed ingredients containing grains, especially wheat, which can then lead to adverse effects on fish when not controlled. F. graminearum mainly produces DON and ZEN as mycotoxins (Marijani 2019). DON-containing feeds fed to chicks causes vomiting (Manning 2010). However, fish are not as susceptible as chicks to DON, albeit exposure to DON can cause reduced feed intake and fish growth (Manning 2010). Commercial feeds for cyprinids have been contaminated by DON and ZEN. The average value of DON concentration was 289 µ g/kg feed while 67.9 µ g/kg feed for ZEN; however, DON contamination is reported to be more prevalent (Pietsch et al. 2013). Fusariumproliferatum This Fusarium species is characterized by cottony colony that has aerial mycelia that can initially appear to be white-colored, although over time it can exhibit greyish white to pale purple pigmentation (Kee et al . 2020). It is a plant pathogen that infects grains and other plants such as soybean (Chang et al . 2015), asparagus (Lori et al . 1998) and onion (Carrieri et al . 2013), mainly by causing root rot. In Uganda, F. proliferatum -contaminated fish feeds have been found to contain fumonisins although F. proliferatum is considered a minor fumonisin-producing fungus ( C O N T I N U E D O N P A G E 6 0 ) corn, spinach and acorn used as an echinoderm feed (Viegas et al. 2019). Interestingly, the isolated fungi were resistant to triazole, a fungicide mainly used to combat fungal growth in corn. Moreover, the two Fusarium spp. were able to produce mycotoxins such as fumonisins for F. verticillioides and deoxynivalenol (DON) and zearalenone (ZEN) for F. culmorum . Fusarium verticillioides has been isolated from an abalone feed containing grain-based ingredients (Greeff-Laubscher et al . 2020) and produced fumonisins upon inclusion in the abalone feed. There was an increased production of the mycotoxin at lower temperatures. The mycotoxin can also leach into seawater when submerged, reducing the risk to abalone health. In Kenya, F. verticillioides was identified as the primary causative agent for significant levels of fumonisins in finished aquafeeds and feed ingredients for rainbow trout and tilapia (Mwihia et al. 2020). Fusariumgraminearum This fungus grows its sexual spores, known as ascospores, in the perithecia, its fruiting body that develops from its mycelium (Beyer and Verreet 2005). Its spores can spread by attaching to the susceptible parts of a plant and usually infects crops like corn and wheat. It can cause Fusarium head blight in wheat and barley (Bai and Shanner 2004) and ear rot in corn (Manning and Abbas 2012). Several mycotoxins from filamentous fungi can thrive in staple agricultural crops such as seeds and nuts, making it a serious food and feed safety concern (Photo: J.A. Ragaza).