Culturable microbiota of ranched southern bluefin tuna (Thunnus maccoyii Castelnau)
Valdenegro Vega, VA and Naeem, S and Carson, J and Bowman, JP and Tejedor del Real, JL and Nowak, BF, Culturable microbiota of ranched southern bluefin tuna (Thunnus maccoyii Castelnau), Journal of Applied Microbiology, 115, (4) pp. 923-932. ISSN 1364-5072 (2013) [Refereed Article]
Aims: The Australian tuna industry is based on the ranching of wild southern
bluefin tuna (SBT, Thunnus maccoyii). Within this industry, only opportunistic
pathogens have been reported infecting external wounds of fish. This study
aimed to identify different culturable bacteria present in three cohorts of SBT
and to determine normal bacteria and potential pathogens in isolates from
harvest fish and moribund/dead fish. Post-mortem changes in the microbiota
were also studied.
Methods and Results: Moribund/dead showed a greater proportion of
members from the family Vibrionaceae than harvested fish; the latter presented
mainly non-Vibrio species. In harvested fish spleens, Vibrio splendidus I
complex was the most commonly identified group among Vibrio isolates, while
most groups from the family Vibrionaceae were isolated from gills. For
moribund/dead, Vibrio chagasii and Photobacterium damselae subsp. damselae
were common in gill, spleen and kidney samples. Non-Vibrio isolates from gills
were characterized using 16S rRNA sequencing as Flavobacteriaceae and classes
Gammaproteobacteria and Alphaproteobacteria, mainly from the genera
Winogradskyella and Tenacibaculum. Post-mortem changes showed dynamic
shifts in bacterial dominance in gills, with Vibrionaceae and non-Vibrio spp.
found in similar proportions initially and types related to Pseudoalteromonas
ruthenica prevailing after 27 h. Spleen samples showed little bacterial growth
until 5 h post-mortem, while various Vibrio-associated species were isolated
27 h post-mortem.
Conclusions: Bacterial isolates found include a range of potentially pathogenic
bacteria that should be monitored though most of them have yet to be
associated with disease in tuna.
Significance and Impact of the Study: This study forms a foundation for
future research into the bacterial population dynamics under different culture
conditions of SBT. An understanding of the bacterial compositions in SBT is
necessary to evaluate the effects of some bacterial species on their health.