Recent update on the prevalence of Vibrio species among cultured grouper in Peninsular Malaysia

Vibrio infections are common among marine fish and lead to serious problems in the aquaculture sector. This study reports a recent occurrence of Vibrio species (spp.) isolated from cultured groupers in Peninsular Malaysia using the gyrB and pyrH genes. A total of 147 Vibrio strains were successfully isolated from 77 (64%) groupers using culture method and subjected to gyrB and pyrH sequencing for species identification and confirmation. Results showed that 89% of Vibrio strains were identified and clustered to six groups of Vibrio spp., while 11% were not clustered to any Vibrio spp. using the gyrB sequences. Meanwhile, by analysis of the pyrH sequences all the 147 Vibrio strains (100%) were successfully identified and clustered into 11 groups of Vibrio spp., including the gyrB non‐identified strains. The pyrH gene provides a better resolution for identification of Vibrio spp. compared with the gyrB gene. Thus, the pyrH gene was more suitable for a rapid determination of Vibrio spp. distribution in Peninsular Malaysia. Using the pyrH gene, our study found higher prevalence of Vibrio vulnificus (33%), V. alginolyticus (24%) and V. parahaemolyticus (22%), followed by V. rotiferianus (5%), V. harveyi (3%), V. tubiashii (2%), V. campbellii (2%), V. ponticus (1%), V. diabolicus (1%), V. owensii (1%) and others Vibrio sp. (7%). Thus, the results of this study revealed that the occurrence of pathogenic vibrios among grouper fish is still high in Malaysian aquaculture. In addition, the pyrH gene was proved as a suitable marker for rapid identification of Vibrio species compared with the gyrB gene.     

Comparative assessment of Vibrio virulence in marine fish larvae

Vibrionaceae infections are a major obstacle for marine larviculture; however, little is known about virulence differences of Vibrio strains. The virulence of Vibrio strains, mostly isolated from vibriosis outbreaks in farmed fish, was tested in larval challenge trials with cod (Gadus morhua), turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus) using a multiwell dish assays with single‐egg/larvae cultures. The strains differed significantly in virulence as some caused a high mortality of larva reaching 100% mortality after a few days, while others had no or only marginal effects on survival. Some Vibrio strains were pathogenic in all of the larva species, while some caused disease only in one of the species. Twenty‐nine of the Vibrio anguillarum strains increased the mortality of larvae from at least one fish species; however, pathogenicity of the strains differed markedly. Other Vibrio species had no or less pronounced effects on larval mortalities. Iron uptake has been related to V. anguillarum virulence; however, the presence or absence of the plasmid pJM1 encoding anguibactin did not correlate with virulence. The genomes of V. anguillarum were compared (D. Castillo, P.W. D'Alvise, M. Middelboe & L. Gram, unpublished data) and most of the high‐virulent strains had acquired virulence genes from other pathogenic Vibrio.     

不同来源海洋弧菌微生物被膜对厚壳贻贝稚贝附着的影响

为探讨广泛存在于近海环境中海洋弧菌和贝类附着的相互作用关系,实验从自然微生物被膜和厚壳贻贝成体肠道内分离了海洋弧菌,测定其种属及亲缘性,调查了这些不同来源弧菌形成的微生物被膜与厚壳贻贝稚贝附着的调控作用。结果显示,测试弧菌形成的微生物被膜密度随着初始细菌密度的增加呈现不同程度的增加。源于自然微生物被膜和贻贝肠道内的10株弧菌均能显著促进厚壳贻贝稚贝的附着,不同菌株形成微生物被膜的诱导活性存在显著差异,附着率变化范围为17%~67%,其中稚贝在Vibrio sp.17微生物被膜上的附着率为67%±2%。微生物被膜对稚贝附着诱导活性与被膜密度呈显著相关性,其中弧菌V.crassostreae ECSMB14106的相关性系数最高,为0.8992。此外,微生物被膜的诱导活性与弧菌的来源无关。本实验初步探明了海洋弧菌对厚壳贻贝稚贝附着的影响,有助于进一步理解微生物被膜调控厚壳贻贝的附着分子机理。     

2株溶藻弧菌烈性噬菌体的分离鉴定及其生物学特性

为寻找并丰富溶藻弧菌噬菌体资源,实验以溶藻弧菌VAHN1为宿主菌,采用双层平板法从海南虾塘水样及福建海产品样本中分离溶藻弧菌噬菌体。通过透射电镜、限制性内切酶及构建发育树等方法对所获溶藻弧菌噬菌体进行分类鉴定;同时分析其生理生化性能。结果显示,本研究分离获得2株溶藻弧菌噬菌体VAP9与VAP21,其噬菌斑均清晰透亮,直径约1.5～2.0 mm。2株噬菌体核酸均为双链DNA,于透射电镜下可见其头部均呈正二十面体结构,2株噬菌体均属肌尾噬菌体科。噬菌体VAP9与VAP21对理化环境具有良好的耐受性;VAP9最适pH为6～8,VAP21最适pH为7～11;2株噬菌体可耐受通用杀菌浓度的过氧乙酸,且对氯仿与乙醚不敏感,同时对紫外线具有一定耐受性。2株噬菌体的最佳感染复数均为0.001,对供试溶藻弧菌的裂解率达95.2%,可裂解部分副溶血性弧菌,但无法裂解除溶藻弧菌与副溶血性弧菌外的弧菌属、葡萄球菌属、假单胞菌属等其他种属的供试细菌。噬菌体VAP9与VAP21可高效抑制溶藻弧菌VAHN1的生长,且2株噬菌体的混合制剂对溶藻弧菌的抑制效果优于单株噬菌体。将噬菌体VAP9及VAP21保守蛋白序列于N...     

Prevalence and antimicrobial resistance of vibrios of human health significance in inland saline aquaculture areas

This study was conducted to evaluate the prevalence, potential pathogenicity and antimicrobial resistance of Vibrio isolates from 65 soil/water/fish samples collected from inland saline aquaculture areas. Depending on the sample type, presumptive Vibrio counts ranged from 2.50 to 6.16 log₁₀ CFU/ml (or/g). Among the 119 confirmed Vibrio isolates, Vibrio cholerae was found to most dominant (91.6%) and it was detected in all the samples from inland saline areas. Seven other Vibrio spp. including Vibrio parahaemolyticus and Vibrio vulnificus were also detected. Except one O139 serotype, rest of the V. cholerae isolates were found belonging to non‐O1/non‐O139 serogroups. None of the V. cholerae isolate was found positive for ctx gene. Antimicrobial susceptibility testing against 7 commonly used antibiotics revealed highest resistance (50.4%) against ampicillin. Very high intermediate resistance (87.4%) was also observed against erythromycin. Contrary to previous studies, high susceptibility (>70%) to chloramphenicol, nalidixic acid, tetracycline and trimethoprim was observed in Vibrio isolates obtained in present study. Almost 20% of Vibrio isolates were resistant to two or more antibiotic classes with multiple antibiotic resistance (MAR) index value of ≥0.28. Presence of V. cholerae isolates with very high MAR index value of 0.85 also suggested that these multidrug‐resistant environment isolates could serve as reservoir of antibiotic‐resistant genes in aquatic systems. The presence of multiple drug resistance vibrios in emerging inland saline aquaculture systems emphasizes the need for their routine monitoring for developing the risk assessment and mitigation strategies.     

Antimicrobial activity of partially characterized analytes from Bacillus pumilus(B2)

This study was carried out to characterize the antimicrobial substance produced by the strain of Bacillus pumilus (B2) obtained from Novozymes Biologicals Inc. to compare its antimicrobial activity by agar well diffusion assay and bacteriocin activity assay via critical dilution method against seven different strains of Vibrio spp., specifically V. alginolyticus (A01), V. cholerae (C01), V. fluvialis (F01, F02), V herveyii (H), V. mimicus (M01), V. parahaemolyticus (P01) and V. vulnificus (V01, V02). All Vibrio spp. were isolated from the hemolymph and intestine of the white faeces disease‐infected moribund pacific white‐leg shrimp Litopenaeus vannamei (Boone 1931) and one strain (V. harveyi) from its diseased postlarva. The cell‐free neutralized supernatant (CFNS) of B2 showed moderate thermo‐stability being stable up to 70°C for 60 min with, however, reducing activity above 80°C for 20 min. B2 antimicrobials showed a stable activity within the pH ranging from 6 to 10 at room temperature and at 4°C, while residual antimicrobial activity of crude CFNS showed tolerance to salinity up to 7% of sodium chloride below 4°C. No B2 activity was obtained while exposed to proteolytic enzyme, such as proteinase k and pepsin, while its activity kept stable exposed to lipase. Initial B2 characterization for antimicrobial substance in CFNS revealed proteinaceous in nature owing to activity loss against proteolytic enzymes and no lipid moiety activity against lipase, which could be categorized as bacteriocin‐like inhibitory substance having potential application against several strains of Vibrio spp. in aquaculture.     

Characterization of two bacteriophages for specific treatment of biofilm formed by a Vibrio sp. isolated from an abalone farm

Vibrio harveyi and related vibrios are potential pathogens causing luminous vibriosis in marine aquaculture systems. In this study, two lytic phages P4A and P4F isolated using Vibrio strains B4A and B4F as indicator bacteria, respectively, were isolated from seawater of an abalone farm. Vibrio strain B4F belongs to the Harveyi clade of the genus Vibrio and was found to cause mortality of abalones in laboratory microcosms. Both phages were able to lyse Vibrio strain B4F. Electron microscopy revealed that phage P4A had an icosahedral head while P4F possessed an elongated hexagonal head. Both phages belong to the family Siphoviridae with long non‐contractile tails. Restriction endonuclease analysis indicated that both phages were double‐stranded DNA viruses and the genome sizes of P4A and P4F were estimated to be about 49 and 44 kb respectively. One‐step growth curves revealed that these two phages exhibited distinct latent periods, exponential periods and burst sizes by infecting the same Vibrio strain B4F. Both phages were able to significantly reduce Vibrio population density in biofilm formed by Vibrio strain B4F on the surface of polyethylene film. It is suggested that these two phages may be promising candidates as biocontrol agents of infections caused by Vibrio strains belonging to the Haveyi clade in marine aquaculture systems.     

Characterization and growth conditions of Vibrio parahaemolyticus strains with different virulence degrees that cause acute hepatopancreatic necrosis disease in Litopenaeus vannamei

The phenotypic characteristics and growth kinetics at several temperatures, salinities, and pH values of three Vibrio parahaemolyticus (Vp) strains with different virulence and one nonpathogenic strain were evaluated. Independent of the virulence of the strain, a high metabolic diversity was found, which yielded different colored phenotypes on the CHROMagar? Vibrio. All strains were resistant to ampicillin and carbenicillin, and Vp AHPND+ organisms were the most sensitive to enrofloxacin. The exponential growth of Vp strains started at 1–2 hr of incubation, although no relationship was observed between the bacterial density and degree of virulence. Moreover, the growth of the most virulent strain was independent of the nutrients in the incubation media during the initial hour postinoculation. No strain grew at 4°C in 0% NaCl and pH 4, but only Vp AHPND+ grew at 44°C. For all strains, the lag phase was proportional to the NaCl concentration, and the growth was better at pH 8–9. However, the Vp AHPND? strain displayed a greater variability, was more sensitive to extreme conditions, and showed a lag phase of 9 hr independent of the pH.     

Probiotics for shrimp larviculture: review of field data from Asia and Latin America

Disease problems have emerged as major constraints in aquaculture production. The prophylactic application of antibiotics is expensive and detrimental, i.e. selection of bacteria that are drug‐resistant or more virulent and the prevalence of drug residues in reared animals. Probiotics, which compete with bacterial pathogens for nutrients and/or inhibit the growth of pathogens, could be a valid alternative to the prophylactic application of chemicals. A mixture of specific Bacillus strains was designed following a research programme on the ability of numerous Bacillus strains to inhibit a range of pathogenic Vibrio strains, to grow under conditions prevailing in shrimp hatcheries and to degrade waste products. These strains were then included in bioassays and challenge tests in order to confirm the lack of toxin production and pathogenicity to humans, target organisms and the environment. Here, we report on the performance of a commercially available mixture of Bacillus strains (SANOLIFE^® MIC), using data from Asian and Latin‐American hatcheries, with Penaeus monodon (Fabricius 1798) and Litopenaeus vannamei (Boone 1931). These results show that probiotics may be a suitable alternative to the prophylactic use of antibiotics. Obviously, minimizing the risk of vibriosis demands a multi‐disciplinary approach, including good hygiene and sanitation measures to reduce the input of potential pathogens, as well as a suitable farm management.     

Exclusion of Vibrio spp. by an antagonistic marine actinomycete Streptomyces rubrolavendulae M56

A marine actinomycete Streptomyces rubrolavendulae M56 isolated from the sediments of Bay of Bengal and displaying biogranulation property was used for the study. The strain showed antagonistic property against vibrios, the opportunistic pathogens in aquaculture. The efficacy of the biogranules of actinomycete M56 in competitive exclusion of Vibrio spp. was tested both in vitro and in vivo. Streptomyces rubrolavendulae M56 biogranules could significantly exclude the pathogenic Vibrio spp. in co‐culture experiments (in vitro). In vivo exclusion of Vibrio spp. in a Penaeus monodon postlarval rearing system was evaluated by treatment of the rearing water with biogranules of S. rubrolavendulae M56. The experiments proved that S. rubrolavendulae M56 biogranules could reduce the pathogenic Vibrio spp., while maintaining total heterotrophic bacterial count. Therefore, the actinomycete biogranules (M56) can be used as a promising alternative to antibiotics in the shrimp larval production system which is often affected by vibriosis.     

Assessment of growth condition for a candidate probiotic, <Emphasis Type="Italic">Shewanella algae</Emphasis>, isolated from digestive system of a healthy juvenile <Emphasis Type="Italic">Penaeus monodon</Emphasis>

To conquer disease problem in shrimp industries, probiotic biocontrol is a well-known remedy now. The antagonistic ability of separated isolates from different parts of juvenile P. monodon was screened against shrimp Vibrio pathogens, V. parahaemolyticus and V. alginolyticus. The most antagonistic effect was observed for an isolate that primarily identified as Shewanella algae using conventional method followed by Biolog GN and GP microplates. Since adaptability to the host optimum cultural condition of the target organism is of the great importance, response surface methodology, with central composite design, was applied to assess log cell count response of S. algae in different incubation conditions. Therefore, four independent variables were assumed as: temperature (10–50°C), pH (6–10), NaCl concentration (0–50‰) and time (12–60 h). The coefficients of multiple determinations (R ²) for the responses log cell count of S. algae being 0.827. Temperature was the merely significant independent variable that affected the log cell count of the candidate probiotic. The candidate probiotic was revealed a reasonable growth response in quite wide range of temperature, pH and NaCl concentration in which the maximum levels were in same range of optimum shrimp culture.     

A selective and differential medium for Vibrio alginolyticus

In this paper, we present a selective and differential medium, termed Vibrio alginolyticus (VAL) agar, developed for the isolation and identification of V. alginolyticus. The presence of bile salts, high salinity and high incubation temperature allows the selective growth of moderately halophilic Vibrio species. Differentiation of bacteria is achieved by identifying species capable of sucrose fermentation, made visible by the pH indicator bromocresol purple. In this study, all of the 26 strains of V. alginolyticus and only three of the 99 strains representing 30 species (including 19 Vibrio species) other than V. alginolyticus were able to grow in the VAL medium. The remaining three strains could be further differentiated from V. alginolyticus according to colour or the diameter of colonies produced on VAL agar plates. Colonies isolated from shellfish rearing water and infected shrimp through the use of VAL agar plates were all positively identified as V. alginolyticus by conventional tests and 16S rDNA sequencing. The testing of specificity and differentiation capability of VAL shows the potential of the agar as a medium for the primary isolation of V. alginolyticus from pathological and environmental samples.     

Isolation and use of beneficial microbiota from the digestive tract of lions‐paw scallop Nodipecten subnodosus and winged pearl oyster Pteria sterna in oyster aquaculture

We isolated microbiota from the digestive tract of Nodipecten subnodosus and Pteria sterna and determined in vitro their haemolytic activity, antagonism against Vibrio spp., bacterial hydrophobicity, production of extracellular enzymes and molecular identification. Five bacterial strains were selected: RL5 and C3 (Lactobacillus spp.) and PB1‐1, PB1‐5 and PB1‐6 (Bacillus spp.). The RL5 and C3 isolates showed antimicrobial activity against Vibrio spp. and the PB1‐1, PB1‐5 and PB1‐6 isolates showed enzymatic activity for amylase, protease, lipase and cellulose; the C3 and PB1‐5 isolates were highly hydrophobic. The selected strains of bacteria were tested in vivo as probiotics, together with a treatment of ampicillin and a control without bacteria on juvenile Kumamoto oysters Crassostrea sikamea. The strains were provided individually and as mixes of isolates. Survival, growth and biochemical composition of the juveniles were determined as in vivo indicators. Juveniles grew significantly larger and faster when treated with a specific mix of isolates (MIX‐B), compared with the control. The protein, lipid and carbohydrate concentrations were also significantly higher in oysters exposed to probiotic treatments, compared with the control and the antibiotic treatment. The selected microbiota showed probiotic proprieties for cultivating C. sikamea juveniles.     

Electrical stunning of farmed Atlantic cod Gadus morhua L.: a comparison of an industrial and experimental method

An industrial and experimental electrical method for stunning farmed Atlantic cod in air and seawater (SW), respectively, were compared. The impacts of sedation with AQUI‐S^? and exercise to exhaustion before electrical stunning were also assessed to monitor the possible depletion of rested muscle energy levels by electrical stunning. Stress (blood glucose, haematocrit, muscle pH, muscle excitability, high‐energy phosphates and rigor mortis) and flesh quality (fillet texture, colour, liquid leakage (LL), gaping, residual blood and K‐value) were assessed. For the industrial stunning method, an average of 41 V, 0.2 A dc was applied to individual cod for 18–27 s. For the SW method, a bipolar square wave current (170 Hz, 33% duty cycle) was applied for 5 s. After stunning, recovery was prevented by exsanguination in chilled SW. There were no differences (P>0.05) between the two stunning methods except for a higher ultimate fillet pH for cod stunned in air 8 days postmortem. Exercise before stunning depleted muscle energy levels at slaughter, increased LL and fillets had redder and darker flesh after storage on ice for 8 days. Electrical stunning (in air) of AQUI‐S^?‐treated fish partly depleted muscle energy levels (pH 7.3, ATP 18.7 μmol g^?1, PCr 70.1 μmol g^?1). However, flesh quality was not affected. Unless pre‐rigor filleting is the chosen processing strategy, electrical stunning of cod seems to be a promising stunning method.     

Susceptibility of corkwing wrasse Symphodus melops, goldsinny wrasse Ctenolabrus rupestis, and Atlantic salmon Salmo salar smolt, to experimental challenge with Vibrio tapetis and Vibrio splendidus isolated from corkwing wrasse

The virulence of two Vibrio strains, previously isolated from diseased corkwing wrasse Symphodus melops and identified as V. tapetis and V. splendidus, to corkwing and goldsinny wrasse Ctenolabrus rupestris and to Atlantic salmon Salmo salar, was studied under laboratory conditions. Both bacteria were shown to be opportunistically pathogenic to corkwing wrasse, causing significantly higher mortality in the challenged groups than in the controls. Bacterial cultivation of kidney samples and re-isolation of V. tapetis and V. splendidus from most mortalities confirmed the two strains as the probable cause of mortality in the challenged groups. The control group also suffered relatively high mortality, but no specific pathogens that were suspected to be the main cause of death were isolated, other than a mixture of Vibrio spp. and, in the case of one individual, atypical Aeromonas salmonicida. Following injection challenge with both bacterial strains, no mortality was recorded in Atlantic salmon. In bath challenge trials with goldsinny wrasse, only slight mortality was observed in the challenged groups and the unchallenged control group. Bacterial examination showed that atypical Aeromonas salmonicida was the probable cause of death in both bath challenged and control groups of goldsinny wrasse, and no indication of infection by any Vibrio sp. was found.     

Use of macroalgae supplemented with probiotics in the Haliotis rufescens (Swainson, 1822) culture in Northern Chile

In this study, we evaluate the use of macroalgae as vectors of probiotics bacteria into the digestive tract of abalone to improve their survival and growth. It is shown that when abalone Haliotis rufescens of different sizes were fed with a natural diet composed of fronds of the macroalga Macrocystis integrifolia supplemented with a mixture of Vibrio sp. C21‐UMA, Agarivorans albus F1‐UMA and Vibrio sp. F15‐UMA bacteria, there was a significant increase (P<0.05) in the average monthly growth rate and survival (%)in a period of 210 days, compared with the control without a probiotic supplement. The permanence of the probiotics in the digestive tract of the animals was monitored, and it was found that the number of culturable C21‐UMA and F1‐UMA bacteria decreased significantly (P<0.05) in recently weaned and adult abalone, and they almost disappeared completely on day 19 of the bioassay. However, the culturable Vibrio sp. F15‐UMA disappeared completely from the digestive tract on day 22 of the bioassay, and these were the bacteria that remained at the highest concentration compared with the other two bacterial strains over the experimental period. It is therefore shown that it is feasible to use a probiotic mixture to improve the profitability of the H. rufescens culture.     

In vitro inhibition of epithelial cell invasion by Aeromonashydrophila Vibrio species by fish Aeromonas hydrophila major adhesin

A virulent strain of Aeromonas hydrophila (PPD 134/91) was obtained from the Primary Production Department, Singapore. Its major adhesin was isolated and purified by potassium thiocyanate extraction and Bio-Gel P-100 gel filtration. The ability of the protein in peak 1, termed major adhesin, to inhibit bacteria from adhering to and invading host cells was studied in vitro using epithelioma papillosum cells of carp (EPC). Results showed that a concentration of 10 μg ml^–1 of this major adhesin could competitively inhibit 28% of A. hydrophila PPD 134/91 from invading EPC cells in vitro. When the concentration was increased to 40 μg ml^–1, the major adhesin significantly cross-inhibited nine other virulent or weakly virulent strains of A. hydrophila. In addition, the major adhesin significantly inhibited not only another bacterial strain from the same family, Aeromonas sobria, but also strains of Vibrio spp. tested. Therefore, we suggest that the major adhesin of this virulent A. hydrophila strain has the potential to be used as a vaccine against the heterogeneous Aeromonas and Vibrio species.     

Probiotic activity of bacteria associated with egg capsules of Concholepas concholepas (common name ‘Loco’)

Egg capsules of Concholepas concholepas were analysed microbiologically, showing the presence of bacteria inside the capsules. The bacteria were isolated and identified, and their probiotic potential on early larvae of C. concholepas was evaluated. From 32 capsules that were examined, 45 bacterial strains were isolated, of which 67% belonged to the genus Bacillus. Survival bioassays were carried out with all the isolated bacterial strains on C. concholepas larvae. It was found that 71% of the bacteria had positive effects on larval survival. This research determined that bacteria of the genera Bacillus and Vibrio present in the capsules have probiotic potential. The bacteria that led to the greatest larval survival were Bacillus pumilus, which may be used in the cultivation of C. concholepas, because one of the limiting factors for the cultivation of this species is larval survival; thus, we propose that the probiotic strains identified in this study will be used during the cultivation of C. concholepas to enhance the chances of larval survival.     

Effect of temperature,pH, antibiotics,formalin and malachite green on the growth and survival of Saprolegnia and Achlya parastic on fish

Twenty-four strains of Saprolegnia and Achlya were isolated from different fish-rearing ecosystems and from diseased carp. Special test methods were developed to measure growth of the strains at different pH and temperature levels. Sensitivity and survival were determined for antibiotics and for 40 concentrations of formalin, malachite green and formalin-malachite green mixture.Out of the 33 antibiotics tested only nalidixic acid exerted a significant growth inhibiting effect. The minimum bathing treatment times necessary for 100% mortality (LT 100) at the different concentrations were determined, and then efficiency curves were constructed by means of computerized analysis of the data. A wide choice of concentrations and treatment times is suggested for practical use.     

Sources of Vibrio bacteria in mollusc hatcheries and control methods: a case study

Results of a 1‐year intensive monitoring of Vibrio bacteria, as thiosulphate citrate billar salt sucrose (TCBS) counts, in a hatchery for molluscs, are presented. Surface seawater, well seawater, tap water from a freshwater well, microalgae system, including pasteurized well seawater, f/2 medium, starter cultures of eight micro algal species, mass‐produced microalgae and compressed air were studied as possible sources of Vibrio. Additionally, recently collected broodstock of the catarina scallop Argopecten ventricosus (Sowerby II 1842) was also subjected for investigation for their possible role in discharging Vibrio during spawning. Efficiency of a cartridge–ultraviolet (UV)‐filtration system and of a steam gun employed for sterilizing tanks, hoses and utensils was also determined. Results indicated that Vibrio were present in surface seawater throughout the year. In well seawater these bacteria were only found during the first 5 months soon after construction of the well and before commencement of continuous operations, but not after this period. Vibrio was never detected in pasteurized well seawater, f/2 medium, starter cultures of microalgae and compressed air. However, mass‐produced microalgae contained Vibrio, possibly as a result of the use of contaminated tap water for washing and rinsing the fibreglass culture tanks. Scallop broodstock was found to be an important source of Vibrio in the hatchery. Biopsy on female gonads of live organisms demonstrated higher numbers of colony‐forming units than male gonads. At spawning, Vibrio was released into water, producing bacterial blooms in tanks after 24 h. The cartridge–UV‐filteration system was not sufficient to eliminate the bacteria from seawater, but the steam gun proved to be a good tool to eliminate Vibrio biofilms on tank walls or tools used in the hatchery. Some recommendations are given, which could be useful for other mollusc hatcheries.