Browsing by Author "Laubscher, Mariska Riana"

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    Mycotoxin contamination of abalone feed : health and safety considerations for the abalone aquaculture industry
    (Stellenbosch : Stellenbosch University, 2016-12) Laubscher, Mariska Riana; Jacobs, Karin; Marais, Gert J.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Abalone farming in South Africa is the largest contributor to the marine aquaculture industry in South Africa and forms part of the worldwide seafood supply chain. Abalone farming has been highly successful, with a consistent positive growth rate over the past decade. However the continued growth rate is dependent on a steady supply of feed resources. Kelp (Ecklonia maxima) has been the main feed source for years, but artificial feed has quickly made an impact on this industry, by showing to be more beneficial to farmers in more ways than one. It has become the main feed source on most commercial abalone farms in South Africa, and consists of a variety of grains, often locally sourced, a protein source and vitamins. In these feeds, natural fungal and mycotoxin contamination is therefore unavoidable. The current study has shown that although, natural mycotoxin levels in abalone feed were low, a number of natural toxigenic fungal species were present in feed samples. There are currently no limits for the allowable mycotoxin concentrations in abalone feed, but naturally occurring mycotoxin levels measured during this study, shown in Chapter 2, have all been substantially lower than the allowable mycotoxin contamination for catfish feed reported by the U.S. Food and Drug association (FDA). The toxigenic fungi isolated represented three toxigenic fungal genera namely Fusarium, Aspergillus and Penicillium. In Chapter 3, some of these fungal isolates were shown to be able to produce high levels of mycotoxins when re-inoculated and left to colonise abalone feed. Results in Chapter 4 showed that fumonisin production by Fusarium verticillioides were higher at 16 °C than at 26 °C. Furthermore, it was found that fumonisins leach into the water when exposed to seawater. These findings together with the high dilution factor and low levels of naturally occurring fumonisins in abalone feed, indicates that it is unlikely that fumonisins hold a threat to the abalone aquaculture industry. However, it remains unclear what will happen to other mycotoxins when exposed to seawater. From the results of this study, production of other mycotoxins by toxigenic fungi can be expected in poor storage conditions. This dissertation ends with recommendations to abalone farmers to lower the overall risks of fungal and mycotoxin contamination in abalone feed.