International Journal of Aquaculture, 2017, Vol.7, No.23, 143-158
154
capable of tolerating fish bile juice to a much higher concentration than that they normally encounter in the GI
micro-environment. Thus, the study might suggest that extracellular enzyme-producing gut bacteria and yeast may
restrain the growth of some fish pathogens and tolerate conditions within the GI tract. The present observation
was in agreement to the previous reports establishing probiotic attributes of fish gut bacteria (Geraylou et al., 2014;
Dutta and Ghosh, 2015; Dutta et al., 2015; Mukherjee and Ghosh, 2016). Although to the author’s knowledge,
such attempt has never been made to characterize yeasts as likely probiotics.
Safety of the host is an important criterion for any probiotic organism as recommended elsewhere (Verschuere et
al., 2000). In this study, the selected isolates were evaluated for safety measurement through small scale
in vivo
study and experimental results revealed that the isolates did not induce any pathological signs or mortalities in
O.
niloticus
. In addition, co-culture of the selected strains with previously isolated autochthonous fish gut bacteria
did not affect growth of the later. Thus, in accordance to some of the preceding reports (Banerjee and Ghosh, 2014;
Banerjee et al., 2016), present study might corroborate the likely co-existence of a diverse autochthonous gut
microflora with the putative probiotic strains selected in the present study.
In this study, we isolated gut microorganisms and tested different probiotic characteristics of them through
in vitro
methods. However, assumptions based on
in vitro
experiments might not conform exactly to
in vivo
conditions.
Although, the autochthonous organisms isolated from the host fish might be better suited to survive and colonize
within the GI tract of the same fish. Nevertheless, extensive
in vivo
studies are warranted with these
autochthonous organisms to determine their effects on overall growth and disease resistance in
O. niloticus
.
Therefore, an evaluation of their role
in vivo
should be given high precedence in future studies.
Authors’ contributions
KG: designed and supervised the study, contributed in the MS, carried out sequence analyses; SB: carried out pathogen inhibition,
co-culture, gut stability and bio-safety studies, prepared the MS; UMM: isolated and maintained bacteria samples, carried out 16S
sequencing works; HAK: isolated and maintained yeast samples, carried out 18S sequencing works; DD: carried out enzymological
works, contributed in sequence analyses.
Acknowledgements
The authors are grateful to the Head, Department of Zoology, The University of Burdwan, West Bengal, India; The Department of
Science and Technology (FIST and PURSE programme), New Delhi, India; and The University Grants Commission
(UGC-SAP-DRS programme), New Delhi, India for providing the research facilities.
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