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Biological Control of Fungi and Mycotoxins in Aquaculture Feeds

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By Milthon Lujan

Biocontrol activity of BC344–2 against toxigenic fungi at day 7 of coincubation. B. cereus BC344–2 antifungal activity was tested against Penicillium, Fusarium and Aspergillus fungi. Source: Bashorun et al., (2023), Aquaculture.
Biocontrol activity of BC344–2 against toxigenic fungi at day 7 of coincubation. B. cereus BC344–2 antifungal activity was tested against Penicillium, Fusarium and Aspergillus fungi. Source: Bashorun et al., (2023), Aquaculture.

The majority of globally marketed fish feeds contain plant-based ingredients, providing an ideal substrate for the development of toxigenic fungi and, under favorable conditions, their synthesis of mycotoxins. A spectrum of mycotoxins looms over the world of aquaculture, particularly in fish farming, where their presence can wreak havoc on cultivated fish species.

In an innovative study, researchers from Qatar University and the Ministry of Municipality and Environment have delved into this issue, investigating the prevalence of mycotoxins in aquaculture feeds and fish tissues. They propose an innovative biocontrol approach using Volatile Organic Compounds (VOCs) emitted by a novel Bacillus cereus BC344–2 strain.

Threat of Mycotoxins in Aquaculture

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According to the study, in aquaculture feeds containing plant-based ingredients such as wheat, corn, and soybean meal, the risk of mycotoxin production (especially AF and OTA) increases during prolonged storage in warm and humid environments. This facilitates the active colonization of fungi, primarily Aspergillus and Penicillium spp.

There is overwhelming evidence of co-contamination when feed or ingredients are infected with fungi capable of producing multiple toxins.

Study Methodology

The study began by collecting samples of aquaculture feeds and fish tissues, analyzing them to isolate fungi and assess mycotoxin presence. Aflatoxins (AF) and ochratoxin A (OTA) took center stage, with a comparative analysis of their levels in muscles and organs of three different fish species.

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Presence of Fungi in Aquatic Feeds

According to the study results, aquaculture feed samples showed a moderate fungal load, dominated by Aspergillus and Penicillium fungi. Mycotoxin analysis revealed the presence of OTA and AF in a substantial percentage of samples, with a notable co-contamination rate of 66.7%.

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Concerning contamination levels, none of the AF-contaminated samples exceeded the EU permissible limits of 20 μg/kg. However, for OTA, 4.8% of samples exceeded the permissible limit of 5 μg/kg.

Fish Tissues Under Scrutiny

While both mycotoxins were detected in liver samples, an intriguing finding emerged: none of the fish meat (muscle) samples showed contamination with OTA. Although AF content complied with permissible limits, a small percentage of samples exceeded OTA limits, emphasizing potential risks associated with mycotoxin exposure.

Bacterial Biocontrol

The application of chemical pesticides in crops is the most suitable control strategy for fungi and mycotoxins. However, residual pesticide transmission and the development of resistant fungal strains pose significant challenges.

The study explored the inhibitory effects of emissions from the Bacillus cereus BC344–2 bacteria and its VOCs on the growth and mycotoxin production of notorious fungi such as Penicillium spp., Aspergillus spp., and Fusarium. In vitro biocontrol co-incubation assays revealed significant inhibitory effects, with P. verrucosum showing the highest sensitivity.

Bioactive Compounds in Action

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Gas chromatography-based analysis of BC344-2 volatilome uncovered five bioactive compounds, with BHT aldehyde and 1-heptadecanol emerging as potential antifungal agents responsible for inhibitory effects on mycotoxin-producing fungi.

Conclusion

“Our findings demonstrate that aquaculture feeds marketed in Qatar from some Asian and European countries generally are contaminated with moderate levels of toxigenic fungi and mycotoxins. While individual mycotoxin levels generally fall within permissible limits, the simultaneous occurrence of two toxins, AF and OTA, in food samples could lead to synergistic effects on aquaculture fish and subsequently, consumer health,” the scientists concluded.

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Regular monitoring of mycotoxins, along with the innovative biocontrol strategy involving BC344-2 VOCs, offers a promising avenue to ensure the well-being of aquaculture environments.

The researchers highlighted, “Considering the inhibitory effect of antifungal volatile compounds from B. cereus (B344-2) on the growth and mycotoxin production of representative fish feed isolates, the bacterial isolate may be applicable in food preservation against fungal attacks and mycotoxin accumulation.”

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As we navigate the complexities of mycotoxin risks, the integration of volatile bacteria emerges as a valuable tool in our arsenal to maintain feed and food safety in the dynamic world of aquaculture.

The study was funded by the Qatar National Research Fund.

Contact
Samir Jaoua
Department of Biological and Environmental Sciences, College of Arts and Science, Qatar University
P.O. Box 2713, Doha, Qatar.
Email: samirjaoua@qu.edu.qa

Reference (open access)
Abdulfattah Bashorun, Zahoor Ul Hassan, Mehsin Al-Ansi Al-Yafei, Samir Jaoua. 2023. Fungal contamination and mycotoxins in aquafeed and tissues of aquaculture fishes and their biological control, Aquaculture, Volume 576, 2023, 739892,ISSN 0044-8486, https://doi.org/10.1016/j.aquaculture.2023.739892.

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