World Aquaculture Magazine - June 2021

60 JUNE 2021 • WORLD AQUACULTURE • WWW.WA S .ORG (Namulawa et al. 2020). Fusarium proliferatum , along with F. verticillioides , is considered to be the main source of fumonisin contamination of feedstuffs in the USA, southern Europe and Mexico (Anukul et al . 2014). Fusarium proliferatum has been isolated from shrimp feed and molecularly identified via internal transcribed spacer-based sequencing (Anukul et al . 2014). Further sequence analysis and enzyme-linked immunosorbent assay showed that the fungi tested positive for the presence of fumonisin-producing genes. Fumonisins from this fungus have been identified in rainbow trout and tilapia feeds in Kenya (Mwhia et al . 2020). Fusarium Mycotoxins and their Effects on Fish Health Fumonisins Fumonisins are the main mycotoxin produced by F. verticillioides and F. proliferatum. These mycotoxins have a same molecular backbone as sphingolipids (ApSimon 2001) that is synthesized into an acetate-based precursor from alanine condensation (Kumar et al . 2013). The FUM1 gene encodes for polyketide synthase enzyme that is responsible for biosynthesis of fumonisins. Molecular detection of the gene can serve as a marker for fumonisin contamination (Sànchez-Rangel et al . 2005). Although fumonisins can be degraded during feed processing (Pietsch 2020), it directly affects fish health at certain levels of contamination. According to the Commission of the European Communities (2006), finished feeds for fish should contain fumonisins at less than 10 mg/kg. Significant reduction in feed intake, weight gain, and hematocrit levels were observed in channel catfish exposed to fumonisins at 20-40 mg/kg for ten weeks (Yildirim et al . 2000). In Nile tilapia, only reduced weight gain and hematocrit were observed when dosed with fumonisns at 10-150 mg/kg (Tuan et al . 2003). This shows that sensitivity to mycotoxins is species-dependent. Fumonisins are also toxic to common carp Cyprinus carpio . A study by Pepeljnjak et al . (2003) showed that exposure to fumonisin B 1 can cause reduction in body weight and skin lesions. Increased levels of serum and hematological parameters, such as platelet and RBC count, bilirubin, creatinine, alanine aminotransferase and aspartate aminotransferase, shows that fumonisins can directly affect activities in liver and kidney of fish. More than one mycotoxin, also known as co-occurrence, can cause adverse effects on fish health. Dietary mixtures of fumonisin and aflatoxin were fed to juvenile African catfish Clarias gariepinus . Hematological analysis indicated lower red blood cell count, hematocrit and haemoglobin concentration. Moreover, significant growth reduction was also observed. The study also reported that catfish can thrive up to 24.5 mg/kg fumonisin and 17.6 µ g/kg aflatoxin (Adeyemo et al . 2018). Corn is commonly contaminated with mycotoxins produced by Fusarium and Aspergillus sp (Photo: J.A. Ragaza). Constant screening of grain-based raw materials and finished feeds for fungal and mycotoxin contamination reduces the risk of feed and culture loss (Photo: J.A. Ragaza).