Elsevier

Aquaculture

Volume 511, 15 September 2019, 734210
Aquaculture

Contrasting outcomes of Vibrio harveyi pathogenicity in gilthead seabream, Sparus aurata and European seabass, Dicentrachus labrax

https://doi.org/10.1016/j.aquaculture.2019.734210Get rights and content

Highlights

  • V. harveyi strain isolated from ascitic fluid collected from cultured gilthead seabream was used in an experiment involving the two most important fish species in Mediterranean aquaculture: gilthead seabream, Sparus aurata and European seabass, Dicentrarchus labrax.

  • Few external signs of carrier-status of V. harveyi were observed, although significant internal histopathological responses were present in hepatic and mucosal tissues.

  • Results of pathogenicity trials shown only 25% mortality in seabream injected with 107 CFU mL−1, whereas, for seabass, a mortality of 95% was recorded, with clear signs of vibriosis.

  • Although for both species, no horizontal transfer of infection was observed in a co-habitation trial for both species, the risk of occurrence between carriers and immunosuppressed individuals or between different species should be considered.

Abstract

Vibrio harveyi has been reported as the dominant heterotrophic bacterial species in western Mediterranean coastal areas during warm seasons, and is recognized as an economically significant pathogen for the aquaculture industry. The present work aimed to evaluate the pathogenicity of a V. harveyi strain isolated from ascitic fluid collected from cultured gilthead seabream and then used in a challenge experiment involving the two most important fish species in Mediterranean aquaculture: gilthead seabream, Sparus aurata and European seabass, Dicentrarchus labrax. The ascitic fluid from diseased juvenile seabreams, previously vaccinated against Photobacterium damselae and Vibrio anguillarum, was extracted and bacteria cultivated for isolation and characterization. Additionally, different tissues were sampled for histological evaluation and description. Significant histopathological responses were observed in hepatic and mucosal tissues. One of the strains isolated from ascitic fluid, IRTA 17-43, was selected for a bacterial challenge. Additionally, the attenuation of virulence through sequential passage of the strain on solid media was also assessed. In parallel, a co-habitation trial was performed in order to evaluate the possible transfer of the bacteria between injected and healthy individuals. Pathogenicity trials in gilthead seabream resulted in only 25% mortality when injected with 107 CFU mL−1, whereas, for European seabass, a mortality of 95% was recorded, with clear signs of vibriosis. When passed sequentially on solid media, the strain IRTA-17-43 showed a decrease of 35% in cumulative mortality for European seabass. No apparent transmission of the pathogen occurred during the co-habitation trial for both species. In conclusion, although few external signs of V. harveyi are observed in vaccinated carriers, internal effects of the infection were clear and severe. Although no horizontal transfer of infection was observed, the risk of occurrence between carriers and immunosuppressed individuals or between different species should be considered. This further validates that the establishment of a good health management system within fish farms is of major importance in order to avoid the onset of disease outbreaks.

Introduction

Vibrio spp. are ubiquitous in the marine environment, particularly in tropical and temperate waters, representing the major bacterial pathogens affecting development of fish farming (Austin and Austin, 2012; Vandenberghe et al., 2003; Zorrilla et al., 2003a), especially in the Mediterranean Sea (Pujalte et al., 2003a). One of the most commonly isolated marine Vibrio species, Vibrio harveyi [syn. V. carchariae] (Gauger and Gómez-Chiarri, 2002) is a marine Gram-negative bioluminescent bacteria with a requirement for sodium chloride (Farmer et al., 2005). The species has been described as free-living, associated to some microalgae blooms, or associated to the intestinal microbiota (Makemson and Hermosa, 1999; Miller et al., 2005; Ramesh et al., 1990). V. harveyi has also been reported during warm seasons, as the dominant heterotrophic bacterial species in western Mediterranean coastal areas (Arias et al., 1999; Ortigosa et al., 1994; Pujalte et al., 1999) and elsewhere, that can be present in expansive blooms (e.g. 15,400 km2 of sea surface) in association with species of microalgae (Miller et al., 2005). Moreover, it is recognized as an economically significant pathogen for the aquaculture industry (Cano-Gomez et al., 2009), with some sporadic cases of wound infections in humans also reported (Austin, 2010; Del Gigia-Aguirre et al., 2017).

As a serious pathogen affecting the aquaculture industry V. harveyi has effected many marine vertebrate and invertebrates (Austin and Zhang, 2006), and is frequently isolated from marine bivalves with implications in some mass mortalities of shellfish (Pass et al., 1987; Sawabe et al., 2007; Travers et al., 2008). Additionally, some studies have described V. harveyi as pathogenic for several species of crustacean larvae (Diggles et al., 2000; Karunasagar et al., 1994; Lavilla-Pitogo et al., 1990; Liu et al., 1996; Robertson et al., 1998; Vandenberghe et al., 1999). Moreover, it has also been associated to several opportunistic infections in fish, and responsible for several cases of infectious necrotizing enteritis, which is characterized by redness of the anal area, abdominal swelling with accumulation of ascitic fluid, inflammation of the anterior intestine and necrosis of the posterior intestine (Austin and Zhang, 2006). Several cultured fish species with economic relevance are globally affected, such as rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar L.) (Zhang and Austin, 2000), Senegalese sole (Solea senegalensis) (Zorrilla et al., 2003a), Japanese seabass (Lateolabrax japonicus) (Lee et al., 2002), cobia (Rachycentron canadum) (Liu et al., 2004b), common dentex (Dentex dentex) (Company et al., 1999; Pujalte et al., 2003b), among others.

Gilthead seabream, Sparus aurata and European seabass, Dicentrarchus labrax are presently the dominant fish species cultured along the Mediterranean coast (FAO, 2005-2018). Infections and mortality episodes observed in cultured seabream and seabass seem to be the result of the interaction of several factors such as poor water quality, seasonality, age-related host susceptibility, stress and pathogen virulence (Abdel-Aziz et al., 2013; Austin and Austin, 2012). Moreover, both fish species are often cultivated at the same farms or in very close proximity. Therefore, it is very relevant to assess the level of risk posed by pathogens, which are sharing tank facilities or where both fish species coexist in the same water masses.

Several bacterial species have been described as common pathogens in cultured gilthead seabream (Balebona et al., 1998; Rodgers and Furones, 1998; Toranzo et al., 2005). The genus Vibrio includes opportunistic pathogens that can affect cultured gilthead seabream (Balebona et al., 1998; Haldar et al., 2010) and European seabass (Pujalte et al., 2003b). Pujalte et al. (2003a) reported V. harveyi as the most frequent species recovered from diseased and asymptomatic gilthead seabream cultured in the Spanish Mediterranean area, from larval to commercial sizes. Disease outbreaks due to V. harveyi exhibit clear seasonal variation with increased prevalence coinciding with temperatures above 20 °C (Arias et al., 1999; Pujalte et al., 1999) and it was also suggested that its increased prevalence could lead to co-infection of other bacterial pathogens (Pujalte et al., 2003a). Furthermore, in a recent study, Scarano et al. (2014) demonstrated that gilthead seabream reared in sea cages are a potential source of Vibrio spp. exhibiting resistance against the most commonly used antibiotics. Recently, in a survey assessing the main pathogens threatening aquaculture in the Mediterranean (Vendramin et al., 2016), V. harveyi was recognized as an emerging problem in seabass.

Although bacterial infections in fish farming systems are common, the present study was designed to determine and compare differences in susceptibilities of the two most important fish species in the Mediterranean aquaculture, Gilthead seabream (S. aurata) and European seabass (D. labrax), to a strain of Vibrio harveyi isolated from cultured seabream during a separate previous nutritional trial. This study aimed to assess the risk and the vulnerability of these two species to this strain of V. harveyi encountered in a naturally occurring epizootic event. Additionally, an attempt to attenuate virulence using serial passage on laboratory media was also performed to compare with the virulence observed using the native isolate.

Section snippets

Fish rearing conditions

During October and November of 2017, over the course of a nutritional assay at IRTA facilities (Sant Carles de la Ràpita), located in the western Mediterranean (Tarragona, Spain), some isolated cases of abdominal swelling with an accumulation of ascitic fluid were observed in cultured juveniles of gilthead seabream (mean ± SD; 15.0 ± 0.5 cm length; mean body weight 81.3 ± 3.8 g), with a cumulative mortality of 3%. Initially, fish were stocked in 200 L tanks at a density of 2 kg m−3 under

Pathogen characterization and identification

All bacterial isolates from ascitic fluid of diseased gilthead seabream were Gram negative rods (~1.5 μm × 0.8 μm). On TSA-NaCl plates, colonies were pale cream-colored with a raised center and peripheral swarm rings. On TCBS agar media, the colonies appeared yellow with crenellated edges. The 16S rDNA sequences were compared to the online database GenBank using the BLAST utility and multiple V. harveyi strains were identified as having identical sequences. From this result, the species was

Discussion

Many of the mortalities described in seabreams cultured in the Mediterranean and Atlantic areas have been associated with epizootic events related to vibriosis, including etiology by V. harveyi. In general, this disease in intensive culture systems is characterized by systemic haemorrhagic septicemia with marked abdominal swelling. Internally, congested blood vessels, branchial, hepatic and intestinal hemorrhages and ascites are the most common histopathological signs of this bacterial disease

Acknowledgements

This work has been supported by the project “Nutritional strategies for the improvement of productive performance: the use of functional feeds and health diets in aquaculture (DIETAplus)”, funded by JACUMAR (Ministry of Agriculture, Fisheries and Environment of Spain, MAPAMA) and FEMP (EU), and the MedAID project (Grant agreement No 727315), funded by the European Union‘s Horizon 2020 research and innovation program. Joana P. Firmino have been subsidized by the Industrial PhD program of the

References (56)

  • D.A. Pass et al.

    Investigations into the causes of mortality of the pearl oyster, Pinctada maxima (Jamson), in Western Australia

    Aquaculture

    (1987)
  • M.J. Pujalte et al.

    Virulence and molecular typing of Vibrio harveyi strains isolated from cultured dentex, gilthead sea bream and European sea bass

    Syst. Appl. Microbiol.

    (2003)
  • A.E. Toranzo et al.

    A review of the main bacterial fish diseases in mariculture systems

    Aquaculture

    (2005)
  • M.-A. Travers et al.

    Summer immune depression associated with increased susceptibility of the European abalone, Haliotis tuberculata to Vibrio harveyi infection

    Fish Shellfish Immunol.

    (2008)
  • J. Vandenberghe et al.

    Phenotypic diversity amongst Vibrio isolates from marine aquaculture systems

    Aquaculture

    (2003)
  • S.K. Whyte

    The innate immune response of finfish - a review of current knowledge

    Fish Shellfish Immunol.

    (2007)
  • I. Zorrilla et al.

    Bacteria recovered from diseased cultured gilthead sea bream (Sparus aurata L.) in southwestern Spain

    Aquaculture

    (2003)
  • C.R. Arias et al.

    Low incidence of Vibrio vulnificus among Vibrio isolates from sea water and shellfish of the western Mediterranean coast

    J. Appl. Microbiol.

    (1999)
  • B. Austin et al.

    Vibrionaceae representatives

  • B. Austin et al.

    Vibrio harveyi: a significant pathogen of marine vertebrates and invertebrates

    Lett. Appl. Microbiol.

    (2006)
  • C. Baker-Austin et al.

    Emerging Vibrio risk at high latitudes in response to ocean warming

    Nat. Clim. Chang.

    (2013)
  • C.T. Bergstrom et al.

    Transmission bottlenecks as determinants of virulence in rapidly evolving pathogens

    Proc. Natl. Acad. Sci.

    (1999)
  • J.J. Borrego et al.

    Updated of the pathologies affecting cultured gilthead seabream, Sparus aurata

    Annals Aquacult. Res.

    (2017)
  • R. Company et al.

    Bacterial and parasitic pathogens in cultured common dentex, Dentex dentex L

    J. Fish Dis.

    (1999)
  • B.K. Diggles et al.

    Luminous vibriosis in rock lobster Jasus verreauxi (Decapoda: Palinuridae) phyllosoma larvae associated with infection by Vibrio harveyi

    Dis. Aquat. Org.

    (2000)
  • S.M.A. El-Sharaby et al.

    Bacteriological and histopathological studies on Vibrio species isolated from naturally infected freshwater fish in Delta region, Egypt

    Adv. Animal Veter. Sci.

    (2017)
  • FAO

    National Aquaculture Sector Overview. Visión general del sector acuícola nacional - España

  • J.J. Farmer et al.

    Bergey's manual® of systematic bacteriology

  • Cited by (37)

    View all citing articles on Scopus
    View full text