Abstract
The emergence of commercial fish farming has stimulated the establishment of fish feed factories in Uganda. However, no information is available on the safety of the feed, mainly due to lack of mycotoxin testing facilities and weak regulatory systems. A study was carried out to examine fungal colonization and mycotoxin contamination in fish feed samples (n = 147) of different types collected from nine fish farms (n = 81) and seven fish feed factories (n = 66) in the Lake Victoria Basin (LVB). Fungi were isolated in potato dextrose agar, grouped into morphotypes and representative isolates from each morphotype were identified based on the internal transcribed spacer (ITS) region of ribosomal DNA sequences. Aflatoxin B1 (AFB1) and total fumonisin (combinations of B1, B2 and B3; hereinafter named fumonisin) levels in feed samples were determined by enzyme-linked immunosorbent assay (ELISA). A wide range of fungi, including toxigenic Aspergillus flavus and Fusarium verticillioides, were isolated from the fish feed samples. AFB1 was detected in 48% of the factory samples and in 63% of the farm samples, with toxin levels <40 and >400 µg/kg, respectively. Similarly, 31% of the factory samples and 29% of the farm samples had fumonisin contamination ranging between 0.1 and 4.06 mg/kg. Pellets and powder had higher mycotoxin contamination compared to other commercially available fish feed types. This study shows AFB1 as a potential fish feed safety issue in the LVB and suggests a need for more research on mycotoxin residues in fish fillets.
Highlights
Uganda’s aquaculture industry is rapidly growing, with over 50% of farmed fish produced in theLake Victoria Basin (LVB) [1]
While the scope of the study is limited to the LVB, where these samples were obtained, some of the key drivers of mycotoxin contamination could be similar in other locations, and the findings are a key contribution towards reducing farmed fish exposure to these harmful toxins
Mycotoxygenic fungi of genera Aspergillus, Emericella, Eurotium, Fusarium, Mucor, Penicillum, Rhizopus, and Talaromyces were isolated from commercial fish feed samples from the LVB at variable frequencies
Summary
Lake Victoria Basin (LVB) [1] This rapidly growing industry has led to an increase in the number of Toxins 2020, 12, 233; doi:10.3390/toxins12040233 www.mdpi.com/journal/toxins. Fish feeds are prepared from maize bran, wheat bran, rice bran, soy meal, cotton seed cake, fish meal, bone meal and termites [3,4,5]. Some of these ingredients are vulnerable to contamination and colonization by fungi that produce toxic secondary metabolites called mycotoxins (e.g. aflatoxins, mainly produced by Aspergillus flavus and A. parasiticus, and fumonisins, mainly produced by Fusarium verticillioides) [6]. The mycotoxin levels and safety of fish feed in Uganda has not been well documented [9,10]
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