Bivalve Hatcheries Research Articles

Examination of the effects of highly diluted bioactive compounds on gametogenesis in relation to energy budget and oocyte quality in mussel (Modiolus capax) broodstock

A critical bottleneck for bivalve hatcheries is the availability of mature broodstock with high-quality gametes to ensure the production of healthy spat. The use of highly diluted bioactive compounds (HDBC) has emerged as a novel and prophylactic strategy to improve gonad development, reproduction bioenergetics, and oocyte quality of marine bivalve broodstock. This study evaluates the effect of HDBC formulas to enhance the laboratory-controlled breeding capacity of Modiolus capax adult mussel, selected as a model organism because of its aquaculture potential as an alternative seafood resource. The experimental design included three replicates of three HDBC treatments at 31Centesimal (1 × 10−31) dynamizations using distilled water as the final excipient (TR1: SiT, CaS, HeS; TR2: PhA, FeP, ZnP; and TR3: ViP, ViA, ViT), and two control treatments: C+ hydro-alcoholic solution at 1% (Usual HDBC vehicle) and C- (distilled water) during a 30-day period. As a result, TR1 enhanced energy reserves (lipids and carbohydrates) in all tissues; TR2 promoted an increase in lipid and carbohydrate content in the gonad and their transfer into developing oocytes; TR3 significantly improved gonad development and reproductive capacity of the mussels with the highest proliferation of mature oocytes, enhancing food-nutrient assimilation and energetic reserve transfer from the somatic tissues to the ovary. Additionally, all HDBC formulas recorded a lower (P < 0.05) number of atretic oocytes compared to the untreated animals. This evidence reflects a simultaneous improvement of gametogenesis and energy budget of M. capax broodstock, ensuring sexual maturation and higher-quality oocytes when HDBC are used.

Effect of marennine on the rearing medium and microbiota of Mytilus edulis larvae and its protective effect after exposure to the pathogenic Vibrio splendidus

ABSTRACT Opportunistic pathogens have been associated with yield-limiting factors in bivalve hatcheries. Numerous natural compounds are being investigated for their beneficial effects and potential to enhance larval resistance without requiring antibiotics. One of those is the use of marennine, a blue pigment, originating from the diatom Haslea ostrearia, which has demonstrated a positive effect on larvae survival. The aim of this study was to highlight the protective effect of marennine on Mytilus edulis larvae during bacterial challenges in relation to a potential modification of the marennine-treated larvae microbiota. D-larvae and post-larvae were exposed for 96 h to Vibrio splendidus (106 cell mL−1) with and without mareninne (500 µg L−1). The presence of marennine increased the survival rate of D-larvae exposed to the pathogen. The molecular analysis of the larvae microbiota diversity indicated a modification in the D-larval microbiota’s richness related to survival rates of larvae. Ultimately, our study sheds light on the importance of the larval microbiota in pathogen resistance during the bivalve rearing process.

Development and evaluation of a formulation of probiont Phaeobacter inhibens S4 for the management of vibriosis in bivalve hatcheries

AbstractLarval eastern oysters (Crassostrea virginica) grown in shellfish hatcheries are susceptible to bacterial diseases, particularly vibriosis. Probiotics are microbes that confer health benefits to the host and have been identified as promising tools to manage diseases in aquaculture. The marine bacterium Phaeobacter inhibens S4 (S4) protects larval eastern oysters against challenge with the bacterial pathogen Vibrio coralliilyticus RE22 (RE22). A concentrated liquid formulation of probiont S4 that maintained high cell viability after long‐term storage was developed for commercial use in shellfish hatcheries. The safety and efficacy of the formulation were tested in six different trials in two hatcheries. The S4 formulation was added to C. virginica larvae culture tanks daily at 104 colony forming units (CFU)/mL from Day 1 post fertilisation until Day 6, 12 or 14, depending on the trial. Treatment of larvae in the hatchery with the S4 formulation did not significantly affect the survival and growth of the larvae. Formulated probiont S4 treatment in the hatchery led to a significant increase in relative percent survival (RPS) when larvae were subsequently challenged with the pathogen RE22 (105 CFU/mL) for 24 h in a laboratory challenge as compared to probiotic‐untreated RE22‐challenged larvae (RPS increase of 46%–74%, p &lt; 0.05). These results suggest that this novel S4 formulation is a safe, easy‐to‐use and effective tool in preventing larval losses due to vibriosis in hatcheries.

Growth, survival and fatty acid profile of hard clam, Mercenaria mercenaria, juveniles fed live microalgae diets

AbstractChoice of microalgae diet affects production outcomes in bivalve hatcheries. This study aimed to identify an optimal microalgae diet to improve hard clam, Mercenaria mercenaria, juvenile production. Four microalgae species (Tisochrysis lutea, Pavlova lutheri, Chaetoceros gracilis and Cyclotella nana) in six dietary combinations were fed for 6 weeks; then, growth, survival and fatty acid profiles of juveniles were evaluated. The highest numerical growth and survival of juveniles were attained by feeding a tetra‐species microalgae diet, but no statistical difference was found by feeding bi‐ or tri‐species diets that consisted of a mix of flagellate and diatom microalgae. Significant differences in fatty acid profiles were found among clams fed different microalgae diets. A contrasting polyunsaturated fatty acid (PUFA) profile was found in juveniles fed flagellate‐ or diatom‐only diets. Clams fed flagellate‐only diets contained a higher percentage of docosahexaenoic acid (DHA) but a lower percentage of (n‐6) PUFAs, whereas those fed diatom‐only diets had a higher percentage of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) but a lower percentage of DHA. In contrast, the percentage of EPA, DHA and ARA was neither very high nor very low in juveniles fed the tetra‐species diet. The complementary nutritional profile of the tetra‐species microalgae diet resulted in enhanced production and exhibited a more balanced fatty acid profile in clam tissue. The tetra‐species microalgae diet should be a preferable choice for feeding hard clam juveniles, but the cost of producing multiple microalgae species for hatchery/nursery operations should be taken into consideration as bi‐ and tri‐species diets provided statistically similar growth and survival. Results of this study can be used to improve productivity and profitability in M. mercenaria hatcheries.

Evaluation of bacterial strains to improve the productivity of microalgae used in bivalve hatcheries in Peru

AbstractThe microalgae Isochrysis galbana and Chaetoceros gracilis are part of the basic diet of most bivalve cultures. This study evaluated the supplementation of bacterial strains naturally associated with these microalgae to improve their productivity. Ten bacterial strains collected from I. galbana and C. gracilis commercial cultures used in the larviculture of the Peruvian scallop Argopecten purpuratus were isolated and purified. These strains were individually coinoculated to each microalgal culture to confirm their promoter effect on growth. First, inoculation was carried out in a volume of 500 mL with constant aeration, which allowed the selection of the best bacterial strains. Then, the culture growth performance after transfer from 500 mL to 2 L tanks, with and without bacterial reinoculation during transfer, was monitored. Two bacterial strains, Lysinibacillus fusiformis and Bacillus cereus, significantly improved (α = .05) I. galbana production, whereas three other strains, Lysinibacillus sp., Psychrobacter celer, and Staphylococcus saprophyticus, significantly increased (α = .05) the growth of the C. gracilis culture. The use of microalgae supplemented with bacteria did not significantly affect A. purpuratus larval rearing. Altogether, these results showed the potential of native probiotic bacteria to improve microalgal production within bivalve hatcheries.

Bacteriophage Cocktail for the Prevention of Multiple-Antibiotic-Resistant and Mono-Phage-Resistant Vibrio coralliilyticus Infection in Pacific Oyster (Crassostrea gigas) Larvae.

Vibrio coralliilyticus (V. coralliilyticus) is a pathogen that causes mass mortality in marine bivalve hatcheries worldwide. In this study, we used a bacteriophage (phage) cocktail to prevent multiple-antibiotic-resistant (MAR) and phage-resistant (PR) V. coralliilyticus infection in Pacific oyster (Crassostrea gigas) larvae. To prevent the occurrence of phage-resistant strains and decrease the effect of mono-phage treatment, we prepared a phage cocktail containing three types of V. coralliilyticus-specific phages and tested its prophylactic efficacy against MAR and PR V. coralliilyticus infection. The results of the cell lysis test showed that the phage cocktail showed an excellent bactericidal effect against the MAR and PR variants in contrast to the experimental group treated with two mono phages (pVco-5 and pVco-7). An in vivo test using Pacific oyster larvae also confirmed the preventive effect against MAR and PR variants. In conclusion, the application of the phage cocktail effectively prevented V. coralliilyticus infection in marine bivalve seedling production. Furthermore, it is expected to reduce damage to the aquaculture industry caused by the occurrence of MAR and PR V. coralliilyticus. Therefore, phage cocktails may be used for the control of various bacterial diseases.

Contrasting Immunomodulatory Effects of Probiotic and Pathogenic Bacteria on Eastern Oyster, Crassostrea Virginica, Larvae.

Several Vibrio spp. cause acute and severe mortality events in hatcheries where larvae of bivalve mollusks are reared, potentially leading to subsequent shortage of bivalve seed for the grow-out industry. In particular, strains of Vibrio coralliilyticus have been identified as a major cause of disease in Pacific, Crassostrea gigas, and eastern, C. virginica, oyster hatcheries in the USA of America. Probiotic bacteria are an inexpensive, practical, and natural method of disease control. Previous research shows that pretreatment of larval oysters with probiotic bacteria Bacillus pumilus RI06–95 (RI) and Phaeobacter inhibens S4 (S4) significantly decreases mortality caused by experimental challenge with the bacterial pathogen V. coralliilyticus RE22 (RE22). This study aims to characterize the immune response of 6–10-day-old eastern oyster larvae to experimental challenge with pathogen V. coralliilyticus RE22 and probionts RI and S4. Treatments included (a) pathogen and probiont exposure at a concentration of 5 × 104 CFU per mL (~2500 bacterial cells per larva) for a duration of 6 h, (b) probiont exposure at the same concentration for a duration of 24 h, and (c) probiont RI daily treatment of larvae in the hatchery for 4, 11, and 15 days. Differential gene expression analysis compared pathogen or probiotic-treated transcriptomes to unexposed controls. Probiotic and pathogen treatment led to upregulation of transcripts coding for several immune pattern recognition receptors (PRRs) involved in environmental sensing and detection of microbes in oyster larvae. Larval oyster responses to pathogen RE22 suggested suppression of expression of genes in immune signaling pathways (myd88, tak1, nkap), failure in upregulation of immune effector genes, high metabolic demand, and oxidative stress that potentially contributed to mortality. On the other hand, the transcriptomic response to probiotic bacteria RI and S4 suggested activation of immune signaling pathways and expression of immune effectors (e.g., Cv-spi2, mucins and perforin-2). These key features of the host immune response to probiotic bacteria were shared despite the length of probiotic exposure, probiotic species, and the type of environment in which exposures were conducted. This study suggests that pre-exposure of eastern oyster larvae to probiotics for 6–24 h prior to pathogenic challenge leads to a robust and effective immune response that may contribute to protecting larvae from subsequent challenge with V. coralliilyticus RE22. This research provides new insights into host-microbe interactions in larval oysters that could be applied in the management of vibriosis in bivalve hatcheries.

Selective breeding of edible bivalves and its implication of global climate change

AbstractBivalve molluscs are very nutritious and are an important source of human animal protein. To date, bivalve farming has contributed to about 15% of the mean per capita animal protein intake of approximate 1.5 billion people around the world. Unfortunately, the effects of climate change, mainly global warming and ocean acidification, have had many deleterious effects on bivalve aquaculture, not only leading to mass mortalities of bivalves in farms and hatcheries, but also causing collapse of natural bivalve populations. In response to the recurrent mass mortalities of farmed bivalves, many selective breeding programmes have been launched with the breeding goal of reducing mortality rate caused by disease outbreaks and changing ocean conditions. This article reviews the progress and potential of selective breeding of edible bivalves in the context of global climate change. It is clear from the literature that in terms of environmental sensitivity, and disease resistance and tolerance, selective breeding has great potential for improving the robustness of edible bivalves with significant heritability and genetic gain. Because the robustness of edible bivalves to climate change is a complex trait affected by multiple genes, the application of modern genomic tools in selective breeding is expected to dramatically enhance the accuracy and efficacy of genetic improvements and produce bivalve strains that are robust to climate change. The information in this article is very useful for guidance on adaptation strategies for climate‐smart bivalve aquaculture solutions to be implemented in bivalve hatcheries and farms.

Isolation and Characterization of Two Bacteriophages and Their Preventive Effects against Pathogenic Vibrio coralliilyticus Causing Mortality of Pacific Oyster (Crassostrea gigas) Larvae.

Vibrio coralliilyticus is one of the major pathogens causing mass mortality in marine bivalve larvae aquaculture. To prevent and control Vibrio spp. infections in marine bivalve hatcheries, various antibiotics are overused, resulting in environmental pollution and the creation of multi-drug-resistant strains. Therefore, research on the development of antibiotic substitutes is required. In this study, we isolated two bacteriophages (phages) that specifically infected pathogenic V. coralliilyticus from an oyster hatchery and designated them as pVco-5 and pVco-7. Both phages were classified as Podoviridae and were stable over a wide range of temperatures (4–37 °C) and at pH 7.0–9.0. Thus, both phages were suitable for application under the environmental conditions of an oyster hatchery. The two phages showed confirmed significant bactericidal efficacy against pathogenic V. coralliilyticus in an in vitro test. In the in vivo experiment, the phage pre-treated groups of Pacific oyster larvae showed significantly lower mortality against V. coralliilyticus infection than untreated control larvae. The results of the present study suggest that both phages could be used in the artificial marine bivalve seedling industry; not only to prevent pathogenic V. coralliilyticus infection, but also to reduce antibiotic overuse.

Early biomarker indicators of health in two commercially produced microalgal species important for aquaculture

In bivalve hatcheries, microalgae production accounts for a large proportion of hatchery operation costs. A reliable supply of good quality algae is essential for optimal output. Two commercially important algal species, Tisochrysis lutea (T-Iso) and Chaetoceros calcitrans were grown in batch culture under optimal and high-pH conditions for 7 and 5 days respectively. A suite of parameters were compared to identify those that could be considered as early markers of algal stress. One day after inoculation of both algal species, carbon dioxide (CO2) addition was removed to cause the high pH treatment condition and cultures were monitored to determine any changes in algal health. A variety of indicators of algal function including photosynthetic parameters by Pulse Amplitude Modulation (PAM) fluorometry and morphological and functional changes by flow cytometry were determined in parallel during the pH stress to correlate them and identify parameters that could be used as an early indicator of decreasing algal health. The pH in the sub-optimal treatments was significantly higher compared with controls from 1 day after the removal of CO2 addition. At the same sampling time (Day 2), in the high-pH treatment, the PSII photosynthetic efficiency in the light measured by PAM fluorometry and, chlorophyll fluorescence and reactive oxygen species production measured by flow cytometry were significantly lower for T-Iso, compared with controls. In sub-optimal cultures of C. calcitrans, relative algal size, complexity, chlorophyll and neutral lipid content (as measured by flow cytometry) were higher as early as Day 2, compared with controls. Additionally, the bacterial abundance associated with T-Iso and C. calcitrans cells was increased in the high pH treatment compared with controls, from Day 6 and Day 5 respectively. These responses to a subtle negative change in the culture environment were detected 24 h prior to a change in cell density and indicate the promise of PAM fluorometry and flow cytometry as tools to provide a rapid, sensitive and reliable assessment of microalgal health in a hatchery setting. Such advances in algal health monitoring will improve bivalve production systems.

Does culture supernatant of Haslea ostrearia containing marennine affect short-term physiological traits in the adult blue mussel Mytilus edulis?

Marennine, the blue-green pigment excreted by the pennate diatom Haslea ostrearia has potential for applications as a natural antimicrobial agent in bivalve aquaculture. However, utilization of this pigment should be assessed further prior to its application in bivalve hatcheries. The present study aims to investigate the effect of the culture supernatant of H. ostrearia containing marennine (Blue Water, BW) on physiological rates of adult mussel Mytilus edulis. The hypothesis tested in this study was that BW could alter clearance and respiration rates of adult M. edulis as indicative physiological traits. Furthermore, the effect of BW on veligers and pediveligers larvae was assessed in physiological experiments to determine whether the fixation of marennine by the larvae can influence larviphagy in this species. Our results showed that BW significantly lowered CR by 43% and reduced the oxygen consumption by 30% in adult mussels, as compared to control. In larviphagy experiments, mussels ingested veliger and pediveliger larvae without discrimination between greened or non-greened larvae. Moreover, fixation of BW in bivalve gills at 3 mg L−1 affected the physiological rate but not intensity of larviphagy in adult M. edulis. This study thus provides an insight into the necessity to determine the potential effect of marennine on adult bivalve for the future utilization of this pigment in bivalve hatcheries.

Application of the bacteriophage pVco-14 to prevent Vibrio coralliilyticus infection in Pacific oyster (Crassostrea gigas) larvae

Vibrio coralliilyticus infects a variety of shellfish larvae, including Pacific oyster (Crassostrea gigas) larvae worldwide, and remains a major constraint in marine bivalve aquaculture practice, especially in artificial seed production facilities. In this study, we isolated and characterized the bacteriophage (phage) that specifically infects V. coralliilyticus. The phage was designated pVco-14 and classified as Siphoviridae. We also investigated the potential efficacy of the isolated phage against V. coralliilyticus infection. We conducted a survey to replace the overuse of antibiotics, which generate multi-antibiotic-resistant strains and causes environmental pollution. The latent period of pVco-14 was estimated to be approximately 30 min, whereas the burst size was 13.3 PFU/cell. The phage was found to infect four strains of tested V. coralliilyticus. pVco-14 was stable at wide temperature (4–37 °C) and pH (5.0–9.0) ranges. Eighty-one percent of oyster larvae died in an immersion challenge at a dose 1.32 × 105 CFU/ml of virulent V. coralliilyticus (strain 58) within 24 h. When oyster larvae were pre-treated with the phage before the bacterial challenge (bacterial conc.: 1.32 × 104 and 1.32 × 105 CFU/ml), mortality of the phage-treated oyster larvae was lower than that of the untreated control. These results suggest that pVco-14 has potential to be used as a prophylactic agent for preventing V. coralliilyticus infection in marine bivalve hatcheries and can reduce the overuse of antibiotics.

Harmful or harmless: Biological effects of marennine on marine organisms

Marennine is a water-soluble blue-green pigment produced by the marine diatom Haslea ostrearia. The diatom and its pigment are well known from oyster farming areas as the source of the greening of oyster gills, a natural process increasing their market value in Western France. Blooms of blue Haslea are also present outside oyster ponds and hence marine organisms can be exposed, periodically and locally, to significant amounts of marennine in natural environments. Due to its demonstrated antibacterial activities against marine pathogenic bacteria (e.g. Vibrio) and possible prophylactic effects toward bivalve larvae, marennine is of special interest for the aquaculture industry, especially bivalve hatcheries. The present study aimed to provide new insights into the effects of marennine on a large spectrum of marine organisms belonging to different phyla, including species of aquaculture interest and organisms frequently employed in standardised ecotoxicological assays. Different active solutions containing marennine were tested: partially purified Extracellular Marennine (EMn), and concentrated solutions of marennine present in H. ostrearia culture supernatant; the Blue Water (BW) and a new process called Concentrated Supernatant (CS). Biological effects were meanwhile demonstrated in invertebrate species for the three marennine-based solutions at the highest concentrations tested (e.g., decrease of fertilization success, delay of embryonic developmental stages or larval mortality). Exposure to low concentrations did not impact larval survival or development and even tended to enhance larval physiological state. Furthermore, no effects of marennine were observed on the fish gill cell line tested. Marennine could be viewed as a Jekyll and Hyde molecule, which possibly affects the earliest stages of development of some organisms but with no direct impacts on adults. Our results emphasize the need to determine dosages that optimize beneficial effects and critical concentrations not to be exceeded before considering the use of marennine in bivalve or fish hatcheries.

Environmental Controls of Oyster-Pathogenic Vibrio spp. in Oregon Estuaries and a Shellfish Hatchery.

ABSTRACTVibrio spp. have been a persistent concern for coastal bivalve hatcheries, which are vulnerable to environmental pathogens in the seawater used for rearing larvae, yet the biogeochemical drivers of oyster-pathogenic Vibrio spp. in their planktonic state are poorly understood. Here, we present data tracking oyster-pathogenic Vibrio bacteria in Netarts Bay and Yaquina Bay in Oregon, USA, as well as in adjacent coastal waters and a local shellfish hatchery, through the 2015 upwelling season. Vibrio populations were quantified using a culture-independent approach of high-throughput Vibrio-specific 16S rRNA gene sequencing paired with droplet digital PCR, and abundances were analyzed in the context of local biogeochemistry. The most abundant putative pathogen in our samples was Vibrio coralliilyticus. Environmental concentrations of total Vibrio spp. and V. coralliilyticus were highest in Netarts Bay sediment samples and higher in seawater from Netarts Bay than from nearshore coastal waters or Yaquina Bay. In Netarts Bay, the highest V. coralliilyticus concentrations were observed during low tide, and abundances increased throughout the summer. We hypothesize that the warm shallow waters in estuarine mudflats facilitate the local growth of the V. coralliilyticus pathogen. Samples from larval oyster tanks in Whiskey Creek Shellfish Hatchery, which uses seawater pumped directly from Netarts Bay, contained significantly lower total Vibrio species concentrations, but roughly similar V. coralliilyticus concentrations, than did the bay water, resulting in a 30-fold increase in the relative abundance of the V. coralliilyticus pathogen in hatchery tanks. This suggests that the V. coralliilyticus pathogen is able to grow or persist under hatchery conditions.IMPORTANCE It has been argued that oyster-pathogenic Vibrio spp. have contributed to recent mortality events in U.S. shellfish hatcheries (R. A. Elston, H. Hasegawa, K. L. Humphrey, I. K. Polyak, and C. Häse, Dis Aquat Organ 82:119–134, 2008, https://doi.org/10.3354/dao01982); however, these events are often sporadic and unpredictable. The success of hatcheries is critically linked to the chemical and biological composition of inflowing seawater resources; thus, it is pertinent to understand the biogeochemical drivers of oyster-pathogenic Vibrio spp. in their planktonic state. Here, we show that Netarts Bay, the location of a local hatchery, is enriched in oyster-pathogenic V. coralliilyticus compared to coastal seawater, and we hypothesize that conditions in tidal flats promote the local growth of this pathogen. Furthermore, V. coralliilyticus appears to persist in seawater pumped into the local hatchery. These results improve our understanding of the ecology and environmental controls of the V. coralliilyticus pathogen and could be used to improve future aquaculture efforts, as multiple stressors impact hatchery success.

Viability of dietary substitution of live microalgae with dry Ulva rigida in broodstock conditioning of the Pacific oyster (Crassostrea gigas).

ABSTRACTThe current study evaluated the microalgae replacement by dry macroalgae (Ulva rigida) in the reproductive success and biochemical composition of the Pacific oyster (Crassostrea gigas) during broodstock conditioning. Five nutritional regimes were tested: 100% macroalgae (diet 1), 50% macroalgae+50% microalgae (diet 2), 25% macroalgae+75% microalgae (diet 3) and 100% microalgae (diet 4). An unfed group was used as a negative control. The microalgae blend was composed of 33% Isochrysis galbana and 67% diatoms (75% Skeletonema costatum+25% Chaetoceros calcitrans). Gonadal maturation was reflected in the physiological condition of the individuals. All treatments, except diet 1, showed an increase in condition index and were fully matured at the end of the trial, with the best physiological condition observed in oysters fed diet 3 and diet 4. Protein and total lipid content increased during the conditioning period, whereas glycogen content decreased. Oysters conditioned with diet 3 had higher protein and total lipid content and lower glycogen content than the other treatments. In addition, diet 3 showed the highest percentage of viable veliger larvae. The current study demonstrated that it is possible to replace 25% of microalgae with macroalgae in the broodstock conditioning, minimizing the operative cost in bivalve hatcheries.This article has an associated First Person interview with the first author of the paper.

Three Draft Genome Sequences of Vibrio coralliilyticus Strains Isolated from Bivalve Hatcheries.

ABSTRACTReported here are the genome sequences of three Vibrio coralliilyticus isolates RE87, AIC-7, and 080116A. Each strain was isolated in association with oyster larvae in commercial aquaculture systems. These draft genomes will be useful for further studies in understanding the genomic features contributing to V. coralliilyticus pathogenicity.

Prophylactic effect ofHaslea ostreariaculture supernatant containing the pigment marennine to stabilize bivalve hatchery production

This paper explores the possibility of using the supernatant of Haslea ostrearia culture containing marennine, a natural microalgal pigment, as an antimicrobial in bivalve hatcheries. The blue mussel Mytilus edulis and the scallop Placopecten magellanicus were used as model animals, and the pathogenic marine bacteria Vibrio splendidus was used to induce larval mortality. The hypothesis tested was that V. splendidus pathogenicity in larval rearings can be controlled by using marennine-containing culture supernatants. The effect of three marennine concentrations was tested on a larval rearing over 20 days for M. edulis and 9 days for P. magellanicus. At a low dose (0.1 mg L-1), survival and physiological condition were both higher than in the control. In bacterial challenges, larvae were exposed to V. splendidus for 72 h, with or without marennine. The bacterial challenge caused significant mortality when compared to controls, while the marennine-treated larvae showed significantly higher survival. Results show that marennine is an interesting molecule for pathogen control in hatcheries as it is active at low concentrations and significantly enhanced larval survival and physiological condition. -- Keywords : Bivalve hatcheries ; microalgal by-products ; Haslea ostrearia ; Mytilus edulis ; Placopecten magellanicus ; Vibrio splendidus.

Probiotic Strains for Disease Management in Hatchery Larviculture of the Eastern OysterCrassostrea virginica

ABSTRACT Bacterial pathogens are a major cause of mortality in bivalve hatcheries, and outbreaks can result in shortages of seed supply to the grow-out industry. The use of probiotic bacteria is a potential preventative measure to limit the impact of bacterial diseases. Previous research showed that the marine bacteria Phaeobacter inhibens S4 (S4) and Bacillus pumilus RI06—95 (RI) protect larval eastern oysters (Crassostrea virginica) when challenged with the pathogens Vibrio tubiashii RE22 (now Vibrio coralliilyticus RE22) and Roseovarius crassostreae CV919-312T. In this study, these probiotic bacteria were tested under hatchery conditions. Daily addition of S4 and RI (104 colony forming units (CFU)/ml) to 100-l culture tanks resulted in a significant decrease in the levels of total Vibrios in water and tank surfaces (P < 0.05), but not in oysters. Larval growth and survival was unaffected by the probiotic treatments. Larvae treated with probiotics in the hatchery showed significantly less mortality than...

Recirculation nursery systems for bivalves

In order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O2, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS.

Mechanisms of microbe-microbe-host interactions in a probiont-pathogen-bivalve model

Marine mollusks are filter feeders and thus are continuously exposed to a myriad of microorganisms. While the majority of bacteria likely have no effect on the overall health of the animal, some microbes, including members of the bacteria genus Vibrio, can cause infections that lead to rapid mortality, especially in larval and juvenile bivalves. For example, the oyster pathogen Vibrio tubiashii causes sporadic crashes of larval oyster production in commercial hatcheries. Alternatively, it is also clear that certain beneficial microorganisms can colonize mollusks and provide disease resistance. Such microbes can potentially be developed as probiotic agents to combat disease outbreaks in bivalve hatcheries. To enable the rational development of such microbes as probiotics, a more comprehensive knowledge of the mechanisms involved in microbe-microbe-host interactions is required. In this study, we investigated how the bacterium Phaeobacter gallaeciensis S4Sm reduces mortality of larval oysters when challenged with V. tubiashii. A combination of analytical chemistry, genetic mutation, and both in vitro and in vivo challenge assays were used to interrogate the roles of specific bacterial metabolites and also bacterial behaviors such as biofilm formation. Our results show that the probiotic activity of S4Sm is multifactorial, involving its ability to form extensive biofilms, production of the potent antibiotic tropodithietic acid, and quorum quenching of pathogen virulence genes.