In the dynamic realm of aquaculture, where the delicate balance of aquatic ecosystems meets the demands of intensive production, the search for sustainable alternatives to antibiotics has never been more critical. Aquatic animals face constant stressors in breeding conditions, posing a threat to intestinal health and increasing the prevalence of dysbiosis.
With the tightening restrictions on antibiotics, there has been a paradigm shift towards economically viable, environmentally safe, and sustainable alternatives.
In this context, scientists from The University of Burdwan, the University of Madras, and the Norwegian College of Fishery Science published a scientific review summarizing current knowledge on yeasts (Candida, Cryptococcus, Debaryomyces, Geotrichum, Leucosporidium, Pichia, Rhodosporidium, Rhodotorula, Saccharomyces, Sporidiobolus, Sporobolomyces, Trichosporon, and Yarrowia lipolytica), molds (Aspergillus spp.), and actinobacteria (Streptomyces) as alternatives to widely used conventional bacterial probiotics.
The Rise of Probiotics
In this quest, the application of beneficial microorganisms, particularly bacteria and fungi, as probiotics has gained significant momentum. While conventional probiotics like bacilli and lactic acid bacteria have been extensively studied, fungi and mycelial bacteria resembling fungi (actinobacteria) have taken center stage in recent times.
These ubiquitous microorganisms thrive in environments rich in organic substrates and find fertile ground for growth in both the aquatic environment and the gastrointestinal tract of fish.
Exploring the Frontier of Fungi
Despite the emphasis on bacilli and lactic acid bacteria, the colonization and probiotic potential of yeasts and molds have been somewhat overlooked. Various species belonging to the “Fungi” kingdom, including Candida, Cryptococcus, Debaryomyces, and Saccharomyces, have shown promising roles in nutrition, immunomodulation, and disease prevention in fish.
Yeasts are part of the normal microbiota in wild and cultured fish, and their role in the health and nutrition of these organisms is well-known. Saccharomyces cerevisiae and Debaryomyces hansenii are two of the most popular and widely studied yeast probiotics in fish.
Bioactive compounds such as manno-oligosaccharides and β-glucans, recognized as fungal postbiotics, play a crucial role in enhancing innate immunity and disease resistance in aquatic species.
Mold as a Probiotic
“In addition to the production of digestive/degradative enzymes, some well-recognized functions of Aspergillus include the synthesis of antibacterial substances, reduction of blood cholesterol levels, inhibition of bacterial infections, immune modulation, and reconstruction of the intestinal microbiota,” cited the study authors.
Most studies in fish are associated with Aspergillus spp. Although some molds can produce mycotoxins, A. niger and A. oryzae, which are the predominant species in the Aspergillus genus, confer benefits to the health of aquatic animals.
Actinobacteria, particularly Streptomyces, bring a unique set of attributes. Known for their hydrolytic enzymes and novel secondary metabolites, they show probiotic potential with implications not only in intestinal health but also in improving water quality.
“These unique physiological characteristics of Streptomyces are believed to make them potential probiotics, as the secretion of exoenzymes could facilitate food utilization and digestion in aquaculture animals once they have colonized the host’s intestine,” emphasized the researchers.
Probiotic Mechanisms and Selection Criteria
Understanding the mechanisms through which these fungi and actinobacteria exert their probiotic effects is crucial. From improving nutrient absorption to enhancing disease resistance, the multifaceted functions of these microorganisms contribute to the overall well-being of aquatic species.
Selection criteria, including adaptability to aquaculture conditions and safety for both the environment and species, play a fundamental role in determining the effectiveness of these probiotics.
According to the study, “yeasts or other fungal strains can be isolated on YPD medium (1% yeast extract, 2% peptone, 2% glucose) supplemented with antibiotics (chloramphenicol, 150 mg L-1; tetracycline, 150 mg L-1).”
As research in this field advances, the future of probiotics for aquaculture looks promising. The holistic approach presented in this article provides an overview of the current state of knowledge on yeasts, molds, and actinobacteria as probiotics in fish aquaculture. Future perspectives delve into the untapped potential of these microorganisms, emphasizing their role in shaping the next generation of sustainable and environmentally friendly aquaculture practices.
In conclusion, the integration of fungi and actinobacteria into the realm of aquaculture probiotics marks a paradigm shift, presenting a holistic and sustainable
approach to address challenges posed by stressors and limitations in antibiotic use.
As we unravel the secrets of these microorganisms, we pave the way for a future where aquaculture not only meets the growing demand for seafood products but does so in harmony with the health of aquatic ecosystems.
Reference (open access)
Ghosh, Koushik, Ramasamy Harikrishnan, Abhisek Mukhopadhyay, and Einar Ringø. 2023. “Fungi and Actinobacteria: Alternative Probiotics for Sustainable Aquaculture” Fishes 8, no. 12: 575. https://doi.org/10.3390/fishes8120575