World Aquaculture Magazine - June 2021

WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2021 61 ( C O N T I N U E D O N P A G E 6 2 ) cytotoxicity and significant mortality were observed when zebrafish larvae were exposed at 1000 µ g/L and 900 µ g/LMON, respectively. Detrimental effects on channel catfish growth were also observed when exposed to 20-120 ppmMON. The mycotoxin interferes with the transition reaction from glycolysis to TCA cycle where conversion of pyruvic acid to acetyl-CoA happens (Manning 2010). Nile tilapia are sensitive to MON at 70-150 ppm. Lower feed conversion ratio, weight gain, and hematocrit were observed upon exposure (Nguyen et al . 2003). Beauvericin Beauvericin (BEA) is cytotoxic to fish cell lines (García-Herranz et al . 2019). Beauvericin was detected in fish feed containing plant- based ingredients (Luz et al. 2017) and palatable flesh that may co-exist with ENN (Tolosa et al . 2014), which might impose a risk to consumers. Beauvericin barely degrades during feed manufacture, making it persist in grain-containing feed (Tolosa et al . 2019). In a recent European study, Atlantic salmon and seabass fish muscle did not contain transmissible BEA and ENN, even after the two mycotoxins were detected in feeds. Remarkably, there were no traces of the two mycotoxins in Atlantic salmon and seabass fish fillet and thus was deemed safe for consumption (Nácher-Mestre et al . 2020). Enniatins (ENN) have been found in cereal-containing raw and finished feeds for livestock and fish. It had the highest prevalence in fish feeds in Kenya followed by DON and fumonisin B 1 (Mwihia et al . 2020). Moreover, probable toxicity and occurrence of ENN in Atlantic salmon fillets was identified in silico (Tolosa et al. 2020) . In vitro studies of ENN exposure to livestock showed that transmission of the mycotoxin from feed to animal is possible but at a very low concentration (Krížová et al . 2021). The Way Forward Fusarium mycotoxin contamination is frequently detected in raw and finished aquafeeds, potentially affecting fish performance. The continuous increase of mycotoxin incidence in aquaculture is an important concern to be addressed, especially with the presence of emerging mycotoxins such as MON, BEA and ENN, indicating that further studies are needed. Molecular screening of mycotoxin levels in feeds can decrease mycotoxin-associated losses in the industry. Ongoing screening of rawmaterials and finished feeds is suggested because some mycotoxins are not degraded during feed manufacture. Furthermore, careful selection of rawmaterials used as feed additives and fishmeal replacements is a factor in reducing the risk of Fusarium mycotoxin contamination because the fungi mostly thrive in grains like corn and wheat. The utilization of other plant-based proteins may alleviate the occurrence of some fungal mycotoxins, including Fusarium spp. metabolites. Co-occurrence of different mycotoxins in a single sample has also been identified in several instances. Therefore, studies to understand the synergism among these co-occurring metabolites are needed to better understand their deleterious effects on fish health and growth and to design an effective mitigation plan. Lastly, assertive protocols in feed storage and transportation should be strictly implemented to reduce the prevalence of mycotoxins in feeds. Deoxynivalenol Deoxynivalenol (DON) is another Fusarium mycotoxin that has been detected in several raw and finished aquafeeds. It is mostly produced by F. graminearum in grain-containing products like corn, oats, wheat and barley. It is a cause of ribotoxic stress in humans as it inhibits translation in 60S ribosomes (Pestka and Smolinski 2005). It can also cause acute effects such as nausea, vomiting and diarrhea upon exposure (Mishra 2019). Rainbow trout growth was reduced after short- and long-term exposures to DON. Liver tissues indicated moderate damage such as enzyme deregulation (Gonçalves et al . 2019). Another study (Hooft et al. 2011) corroborated the sensitivity of rainbow trout to DON. When fed with different levels of DON (0.3, 0.8, 1.4, 2.0 and 2.6 ppm) for eight weeks, significant reduction in growth rate, weight gain, feed intake and feed efficiency were noted. Dietary DON has adverse effects on carp health, such as oxidative damage and upregulated apoptosis that reduces gill integrity (Huang et al. 2020) and a significant decline in immune response (Pietsch et al . 2015). Dietary DON also reduces weight gain and mortality and causes intestinal tissue damage in juvenile Pacific white shrimp Litopenaeus vannamei (Xie et al . 2018). A concentration of less than 0.5 ppmDON is considered safe for Pacific white shrimp (Xie et al. 2018). Like fumonisin, DON co-occurs with other mycotoxins in aquafeeds. In a recent study, mixture of two mycotoxins DON and aflatoxin B 1 caused upregulated expression of glutathione redox system in carp kidneys, which is caused by oxidative stress upon exposure to the two mycotoxins (Kövesi et al . 2020). Zearalenone Zearalenone (ZEN) is considered one of the major Fusarium mycotoxins that negatively affects several farmed animals (Zhang et al . 2018). Zearalenone has been detected in aquafeeds in several instances (Gonçalves et al. 2016, Kholife et al . 2019, Nogueira et al . 2020). Immune response gene expressions in common carp liver are reduced after 332-797 µ g/kg ZEN exposure for 28 days (Pietsch 2017). Zearalenone has detrimental effects on growth and intestinal integrity of juvenile grass carp Ctenopharygodon idella . Deformities in the fish body structure, decreased growth rate, and intestinal lesions were observed after feeding fish with increasing levels of ZEN (0, 535, 1041, 1548, 2002 and 2507 µ g/kg) for one week (Wang et al . 2019). Rainbow trout exposed to 2 mg/kg ZEN, considered a safe level according to the European Commission guidelines, had impaired reproductive capability and high mortality after 12-96 weeks of feeding; thus, this current guideline should be revisited (Woźny et al . 2020). Emerging Fusarium Mycotoxins in Aquaculture Moniliform (MON) is another mycotoxin produced by F. verticillioides and F . proliferatum that can directly affect the growth performance of livestock. MON is currently considered as an “emerging toxin,” including beauvericin (BEA) and enniatins (ENN). It contaminates livestock and aquaculture feeds that contain grain and grain-like ingredients. Limited studies have been dealt with its mechanisms and effects on fish performance. A preliminary study was done by Gonçalves et al . (2018) to observethe effects of MON using zebrafish Danio rerio as a model organism. In vitro