Mycotoxin contamination of abalone feed : health and safety considerations for the abalone aquaculture industry

Laubscher, Mariska Riana (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.


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.

AFRIKAANSE OPSOMMING: Perlemoen boerdery in Suid Afrika lewer die grootste bydrae tot marine akwakultuur in ons land. Dié industrie vorm deel van die wêreldwye voedselvoorsienningsketting. Perlemoen boerdery is hoogs suksesvol met 'n konstante jaarlikse groei. Die sukses van die industrie is egter afhanklik van konstante voorsiening van voer. Kelp (Ecklonia maxima) was vir jare gebruik as die enigste voer, maar kunsmatige voer het vinnig ‘n impak op die industrie gemaak en was voordelig op verskeie vlakke. Dit word nou beskou as die hoofbron van voer op die meeste kommersiële perlemoen plase in Suid-Afrika. Kunsmatige voer bestaan uit ‘n verskeidenheid grane, ‘n proteïenbron en vitamiene. Vir die rede is dit natuurlik dat mikotoksien en swam kontaminasie onvermybaar is. Die studie wys dat natuurlike mikotoksien kontaminasie laag was in die kos, maar dat verskeie toksiese swamspesies teenwoordig was in die monsters. Daar is tans geen maksimum toelaatbare vlakke vir mikotoksiene in perlemoenvoer nie, maar die mikotoksien vlakke wat gedurende die studie gemeet was, (Hoofstuk 2), was laer as die toelaatbare vlakke wat voorgeskryf word deur die U.S. Food and Drug association (FDA) vir katvisvoer. Toksiese swamme wat geïsoleer is vanaf perlemoenvoer, verteenwoordig drie genera naamlik Fusarium, Aspergillus en Penicillium. Hoofstuk 3 wys dat van die swamme die vermoeë het om hoë vlakke mikotoksiene te produseer wanneer dit toegelaat word om perlemoenvoer te koloniseer. Resultate in Hoofstuk 4 toon dat fumonisien-produksie deur Fusarium verticillioides op perlemoenvoer hoër was by 16 °C as by 26 °C. Verder is daar gevind dat fumonisiene in die water uit lek wanneer voer aan seewater blootgestel word. Die resultate, tesame met die hoë verdunningsfaktor en lae vlakke natuurlike fumonisienvlakke in die voer is ‘n aanduiding dat dit onwaarskynlik is dat fumonisiene 'n beduidende risiko vir die perlemoenindustrie inhou. Daarteenoor is dit ook onduidelik hoe ander mikotoksiene sal reageer in die teenwoordigheid van seewater. Resultate van die studie toon dat die produksie van ander mikotoksiene op perlemoenvoer verwag kan word, mits opbergingstoestande van voer nie goed gereguleer word nie. Die proefskrif eindig met ‘n paar aanbevelings aan plase om die algehele risiko van mikotoksien en swam kontaminasie in perlemoen voer te verlaag.

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