Mortality event involving larvae of the carpet shell clam Ruditapes decussatus in a hatchery: isolation of the pathogen Vibrio tubiashii subsp. europaeus

Abstract

Diseases caused by bacteria belonging to the genus Vibrio are a common, as yet unresolved, cause of mortality in shellfish hatcheries. In this study, we report the results of routine microbiological monitoring of larval cultures of the carpet shell clam Ruditapes decussatus in a hatchery in Galicia (NW Spain). Previous episodes of mortality with signs similar to those of vibriosis affecting other species in the installation indicated the possibility of bacterial infection and led to division of the culture at the early D-veliger larval stage. One batch was cultured under routine conditions, and the other was experimentally treated with antibiotic (chloramphenicol). Differences in larval survival were assessed, and culturable bacterial population in clams and sea water was evaluated, with particular attention given to vibrios. Severe mortalities were recorded from the first stages of culture onwards. The pathogen Vibrio tubiashii subsp. europaeus was detected in both batches, mainly associated with larvae. Moreover, initial detection of the pathogen in the eggs suggested the vertical transmission from broodstock as a possible source. Experimental use of antibiotic reduced the presence and diversity of vibrios in sea water, but proved inefficient in controlling vibrios associated with larvae from early stages and it did not stop mortalities.

In situ observations and modelling revealed environmental factors favouring occurrence of Vibrio in microbiome of the pelagic Sargassum responsible for strandings

“…Beside profile P-Mex, three extra microbiome profiles were also identified, all of them harbouring Vibrio, at low concentration (1-2%) for P-Rho (n=75), or at higher concentration for P-Alt (6.5%) and P-Vib (28%) (n=25). Among Vibrio OTUs found herein, six potential pathogens have been identified that fell in a cluster containing V. parahaemolyticus, V. alginolyticus, V. campbellii (Ruwandeepika et al, 2012), V. europaeus (Dubert et al, 2016), V. tubiashi (Dubert et al, 2017), and V. ichthyoenteri (Ishimaru et al 1996). Many studies have described the capacity of Vibrio to attach to various organisms, but data of their enrichment compared to the water column is often lacking (Takemura et al, 2014).…”

AHL-lactonase expression in three marine emerging pathogenic Vibrio spp. reduces virulence and mortality in brine shrimp (Artemia salina) and Manila clam (Venerupis philippinarum)

“…Marine pathogenic bacteria can completely kill mollusks, fish and coral populations that are cultivated in aquaculture, causing drastic economic losses [ 71 , 72 ]. Even though antibiotics have been used for many years to control infections, the emergence of antibiotic-resistant strains [ 73 , 74 ] and sometimes the inefficacy of the treatments [ 75 ] make the situation more and more alarming. Global efforts are needed to search for novel strategies to control pathogens in aquaculture and to promote a responsible use of antibiotics to make the industry more sustainable as well as to maintain a healthy environment [ 76 ].…”

New Insights into Pathogenic Vibrios Affecting Bivalves in Hatcheries: Present and Future Prospects

“…Interestingly, Dubert et al (2016e) included in the description of the new taxa a French isolate initially identified as V. tubiashii , and highly pathogenic for C. gigas larvae and spat ( Mersni-Achour et al, 2014 , 2015 ; Travers et al, 2014 ). Recently, Dubert et al (2017) have reported a mortality event in larvae of other clam species, namely R. decussatus , involving this bacterial species. In summary, V. europaeus is an emergent bivalve pathogen responsible of severe losses that affected Spanish and French hatcheries ( Travers et al, 2014 ; Prado et al, 2015 ; Dubert et al, 2016e , 2017 )…”

“…Recently, Dubert et al (2017) have reported a mortality event in larvae of other clam species, namely R. decussatus , involving this bacterial species. In summary, V. europaeus is an emergent bivalve pathogen responsible of severe losses that affected Spanish and French hatcheries ( Travers et al, 2014 ; Prado et al, 2015 ; Dubert et al, 2016e , 2017 )…”