Abstract
Defense mechanisms of fish are investigated in many aspects. One of the most interesting systems is that based on non-specific immune factors whose mechanisms of biocontrol have evolved in complex processes of microbiological co-existence. The wild fish devoid of probiotic stimulation have developed their own system to control the biosynthesis of immunostimulating compounds based on commensal microflora. Results of this study demonstrated the gastrointestinal tract (GI) of wild fish (Abramis brama, Rutilus rutilus, Perca fluviatilis) was colonized by permanently residing strains of Rhodotorula mucilaginosa. The genetic profile of the tested strains (PCR–random amplification of polymorphic DNA) indicated their affinity only to the GI of the analyzed fish. The capability for biosynthesis of β-carotene, torulene, torularhodin, and exopolysaccharides (EPS) under conditions of fish gastrointestinal tract was found to be a strain-specific trait. Rhodotorula spp. interactions with fish should be considered as a mechanism of symbiotic relations based on the stimulation of non-specific mechanisms of fish immunoprotection and antioxidative properties of yeast.
Highlights
The knowledge on the ecological role of microflora of wild fish gastrointestinal tract, especially that associated with yeast prevalence, is still insufficient
The numbers of fungi determined for all fish species ranged from 2.44 to 2.94 log cfu g−1
The number of yeast isolated from epidermal mucus (EM) of all fish in the summer season was statistically lower (2.24–2.63 log) than in the spring and autumn seasons (3.55–4.43 log and 3.68–4.51 log, respectively)
Summary
The knowledge on the ecological role of microflora of wild fish gastrointestinal tract, especially that associated with yeast prevalence, is still insufficient. The functionality of unicellular fungi does not change in time on condition that they represent an element of permanent microbiota In most cases, their counts do not exceed 2.0–5.0% of the total population of microorganisms isolated from fish. As yeast represent a valuable source of enzymes, vitamins, amino acids, and oligosaccharides (Lokesh et al 2012), in the opinion of some scientists, they are better growth promoters than the probiotic bacteria are (Caruffo et al 2015). Their antimicrobiological properties are increasingly often emphasized (Hatoum et al 2012). Investigations on the health-promoting effects of yeast concern mainly Saccharomyces cerevisiae, Debaryomyces hansenii, and Phaffia rhodozyma (Caruffo et al 2015; Irianto and Austin 2002) have been mainly conducted with cultured fish, while the aspect of the ecological role of yeast in wild fish seems to be completely neglected
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