Seasonal variation and effects of age, food availability, size, gonadal development, and parasitism on the hemogram of mytilus galloprovincialis

Specification of hemocyte subpopulations based on immune-related activities and the production of the agglutinin MkC1qDC in the bivalve Modiolus kurilensis

Bivalves, such as Modiolus are used as indicator organisms to monitor the state of the marine environment. Even though hemocytes are known to play a key role in the adaptive and protective mechanisms of bivalves, these cells are poorly studied in horse-mussel Modiolus kurilensis. In this paper, we present classification of horse-mussel hemocytes based on their immune functions, including the production of specific immune-related molecules, as well as their morphological composition after isolation by density gradient centrifugation. An effective fractionation protocol was adapted to separate four hemocyte subpopulations with distinct morphofunctional profiles. First subpopulation consisted of small under-differentiated hemoblasts (2.20 ± 0.85%) with a bromodeoxyuridine positive nucleus, and did not show any immune reactivity. Second was represented by agranulocytes (24.11 ± 2.40%), with evenly filled cytoplasm containing a well-developed protein-synthesizing apparatus, polysomes, smooth endoplasmic reticulum and mitochondria, and positively stained for myeloperoxidase, acidic proteins, glycogen and neutral polysaccharides. Third subpopulation consisted of eosinophilic granulocytes (62.64 ± 9.32%) that contained the largest number of lysosomes, peroxisomes and vesicles with contents of different density, and showed the highest phosphatase, reactive oxygen species (ROS) and phagocytic activities. Lastly, fourth group, basophilic granulocytes (14.21 ± 0.34%), are main producers of lectin-like protein MkC1qDC, recently discovered in M. kurilensis and characterized by pronounced antibacterial and anticancer activity. These cells characterized by intracytoplasmic of the MkC1qDC localization, forming granule-like bodies visualized with specific antibody. Both granulocytes and agranulocytes showed phagocytic activity and ROS production, and these reactions were more pronounced for eosinophilic granulocytes, suggesting that this group is the key element of the cell-mediated immune response of M. kurilensis. Our results support a concept of bivalve's hemocyte specification with distinct phenotypes.

The effect of temperature and challenge route on in vitro hemocyte phagocytosis activation after experimental challenge of common octopus, Octopus vulgaris (Cuvier, 1797) with either Photobacterium damselae subsp. damselae or Vibrio anguillarum O1

Infectious diseases in aquaculture could be associated with high mortalities and morbidity rates, resulting in negative impacts to fish farming industry, consumers, and the environment. Octopods are reared near marine fish farming areas, and this may represent a major risk since fish pathogens may cause pathologies to octopods. Up to date cephalopods immune defense and pathologies, are incompletely understood. Therefore, the aim of this study was to determine the effect of water temperature and challenge route on hemocyte phagocytosis in vitro after experimental challenge of common octopus with Photobacterium damselae subsp. damselae or Vibrio anguillarum O1. Hemolymph was withdrawn at various time-points post-challenge and the number of circulating hemocytes, and phagocytosis ability were determined. No mortalities were recorded irrespective of pathogen, route of challenge and temperature employed. Great variation was observed in the number of circulating hemocytes of both control and challenged specimens in both experiments (1.04 × 10⁵ to 22.33 × 10⁵ hemocytes/ml for the Photobacterium damselae subsp. damselae challenge and 1.35 × 10⁵ to 24.63 × 10⁵ hemocytes/ml for the Vibrio anguillarum O1 and at both studied temperatures). No correlation was found between circulating hemocytes and baseline control specimens body weight. Probably, the number of circulating hemocytes is affected by many extrinsic, and intrinsic factors such as size, age, maturity stage, natural fluctuations and temperature, as indicated in the literature. The hemocyte foreign particles binding ability observed in Photobacterium damselae subsp. damselae experiments, at 21 ± 0.5 °C and 24 ± 0.5 °C, was (mean ± SD) 2.26 ± 2.96 and 11.72 ± 12.36 yeast cells/hemocyte for baseline specimens and 7.84 ± 8.88 and 8.56 ± 9.89 yeast cells/hemocyte for control and challenged specimens, respectively. The corresponding values for Vibrio anguillarum O1 experiments were (mean ± SD) 6.68 ± 9.26 and 7.00 ± 8.11 yeast cells/hemocyte for baseline specimens and 8.82 ± 9.75 and 6.04 ± 7.64 yeast cells/hemocyte for control and challenged specimens, respectively. Hemocytes of the Photobacterium damselae subsp. damselae and Vibrio anguillarum O1 challenged specimens, were more activated at lower temperature. Apparently, temperature is an important factor in hemocyte activation. In addition, our results indicated that time post challenge, route of challenge and pathogen may influence phagocytosis ability.

Bivalve Haemocyte Subpopulations: A Review

Bivalve molluscs stand out for their ecological success and their key role in the functioning of aquatic ecosystems, while also constituting a very valuable commercial resource. Both ecological success and production of bivalves depend on their effective immune defence function, in which haemocytes play a central role acting as both the undertaker of the cellular immunity and supplier of the humoral immunity. Bivalves have different types of haemocytes, which perform different functions. Hence, identification of cell subpopulations and their functional characterisation in immune responses is essential to fully understand the immune system in bivalves. Nowadays, there is not a unified nomenclature that applies to all bivalves. Characterisation of bivalve haemocyte subpopulations is often combined with 1) other multiple parameter assays to determine differences between cell types in immune-related physiological activities, such as phagocytosis, oxidative stress and apoptosis; and 2) immune response to different stressors such as pathogens, temperature, acidification and pollution. This review summarises the major and most recent findings in classification and functional characterisation of the main haemocyte types of bivalve molluscs.

The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as 'high risk' for consumer health.

Green-lipped mussel (Perna canaliculus) hemocytes: A flow cytometric study of sampling effects, sub-populations and immune-related functions

Green-lipped mussels (Perna canaliculus) are a commercially and culturally important bivalve species in New Zealand (NZ). As the highest value export aquaculture product in NZ, understanding and safeguarding the health of this species is imperative. The identification and characterization of hemocytes can provide useful information regarding the health of this species. Using flow cytometry (FCM), the present study assessed for the first time the use of different antiaggregant solutions and storage times on the immune-related parameters of hemocytes from cultured adult P. canaliculus. In addition, characterization of the immune-related functions of hemocyte sub-populations within the hemolymph were assessed. The two antiaggregant solutions tested (Modified Alserver's, MAS, A and B) maintained similar numbers of hemocytes in circulation over a 60 min period but, reduced the viability (MAS A) and increased the ROS production (MAS B) of the hemocytes compared to hemocytes diluted in cold filtered seawater (FSW). Hemocytes diluted in FSW and kept on ice showed significant aggregation after 2 h and a reduction in viability from 4 h. Three different hemocyte sub-populations were identified, discernible by their relative size and internal complexity: blast-like cells, hyalinocytes and granulocytes, which accounted for approximately 4, 67 and 29% of the total hemolymph population respectively. Granulocytes showed significantly higher reactive oxygen species production, phagocytic capabilities and neutral lipid content compared to hyalinocytes and blast-like cells. Results indicate that maintaining extracted hemolymph in cold FSW, completing analysis of fresh samples within 2 h of extraction and FCM assay incubation times of no longer than 30 min are best to obtain accurate results. Formalin fixation can also be used for future determination of hemocyte sub-populations and internal structures. Results from this study will allow effective future study of the effects of various stressors on P. canaliculus health and lead to improved management and production strategies in this species.

Field studies on the effects of Marteilia sp. on growth of mussel Mytilus galloprovincialis in Thermaikos Gulf

Global warming may accelerate growth and distribution of pathogens influencing aquatic organisms' diseases and human health. Despite the extensive research, the biology, cellular development and life cycle and of Marteilia sp. parasites as well as the influence of parasitic infection on the hosts are not fully understood. The aim of this study was to investigate the effect of Marteilia sp. prevalence and infection intensity on mussels' growth rate and morphometric characteristics under natural conditions in Thermaikos Gulf, a major bivalve production area in Greece, during a five-month growth period. The length, width, height and weight of the infected mussels were significantly lower compared to non-infected and the decrease was proportional to the intensity of mussel infection by the parasite. Moreover, the estimation of allometric relations between length, height, width and weight revealed significantly lower growth of mussel wet weight in relation to shell length for infected mussels compared to healthy ones. The negative effect of marteiliosis on the shell length growth rate of infected mussels was also confirmed by von Bertalanffy equations.

Proliferation and differentiation of circulating haemocytes of Ruditapes philippinarum as a response to bacterial challenge

Ultrastructural investigation confirmed the presence of four cell types (granulocytes, hyalinocytes, serous cells, and haemoblasts) in the haemolymph of the Manila clam, Ruditapes philippinarum. Granulocytes were characterised by numerous electron-dense granules, whereas hyalinocytes had a considerable number of small clear vesicles. Serous cells exhibited large vacuoles, which filled the cytoplasm, and haemoblasts (the undifferentiated cells) were small roundish cells characterised by a high nucleus/cytoplasm ratio. The presence of circulating haemoblasts was observed at various phases of mitosis. Updated data concerning the proliferation and differentiation of circulating haemocytes were obtained after both in vitro and in vivo bacterial challenge. The results demonstrated that cell proliferation occurred within 15 h of exposure, and most haemocyte types responded to the stimuli. The number of granulocytes significantly decreased after massive phagocytosis and ultrastructural observations confirmed that they were active phagocytic cells against both Gram-positive and Gram-negative bacteria, which were rapidly engulfed into large phagosomes. Granulocyte lysis may represent a protection response against bacterial proliferation inside phagosomes. The number of serous cells significantly increased, suggesting a previously unreported pivotal immune role during bacterial infection. A panel of lectins was used as probes to further characterise haemocytes and their relationships. Only hyalinocytes were not positive for the lectins assayed, whereas all lectins labelled serous cells, suggesting that these cells have a variety of specific carbohydrates, which are shared with certain haemoblasts. The hypothesis of the existence of a prospective haemoblast for serous cell origin is discussed.

Temperature increases, hypoxia, and changes in food availability affect immunological biomarkers in the marine mussel Mytilus galloprovincialis

Temperature increases, hypoxia, and changes in food availability are predicted to occur in the future. There is growing concern for the health status of wild and farmed organisms, since environmental stressors alter organism functions, and elicit coordinated physiological responses for homeostasis. Mussels are good bioindicators of environmental conditions. Their ability to maintain unaltered immunosurveillance under adverse environmental conditions may enhance their survival capability. Few studies are currently concerned with the relationships and feedback among multiple stressors. Here, food concentration, temperature, and oxygenation treatments were evaluated for their effects on immune enzymatic parameters of Mytilus galloprovincialis detected in the digestive gland and the lysosomal viability by neutral red uptake. Mussels were exposed to three temperatures (12, 20, and 28 °C) under normoxic (8 mg O₂l^-1) and anoxic conditions and specimens were fed with six food concentrations, ranging 0.2-5 g chlorophyll l^-1. Temperature increases affected esterase and alkaline phophatase enzyme functionality, and addition of food buffered detrimental effects generated by harsh conditions, such as those provided by low oxygen concentrations. Kinetics of the phenoloxidase was negatively correlated with increasing temperature. In this case, food had a buffering effect that counteracted the limiting temperature only under normoxic conditions. In addition, the stability of the lysosomal membrane was altered under conditions of thermal stress and food change, under normoxic and anoxic conditions. Overall, environmental stress factors affected immune biomarkers of Mediterranean mussels, and the level of food acted as a buffer, increasing the thermal resistance of the specimens.

Functional features of hemocyte subpopulations of the invasive mollusk species Dreissena polymorpha

Dreissena polymorpha is a mussel species that invaded many lotic and lentic inland waters in Western Europe and North America. Its positive or negative interactions with biotic and abiotic components of ecosystems are numerous, making this bivalve the subject of numerous studies in ecology, ecophysiology and ecotoxicology. In these contexts, the functional characterization of the zebra mussel hemocytes is of particular interest, as hemocytes are central cells involved in vital functions (immunity, growth, reproduction) of molluscan physiology. Dreissena polymorpha circulating hemocytes populations were characterized by a combination of structural and functional analysis. Assessments were performed during two contrasted physiological periods for mussels (gametogenesis and spawning). Three hemocyte types were identified as hyalinocytes and blast-like cells for agranular hemocytes and one granulocyte population. Flow cytometry analysis of hemocytes functionalities indicated that blast-like cells had low oxidative and mitochondrial activities and low lysosomal content. Hyalinocytes and granulocytes are fully equipped to perform innate immune response. Hyalinocytes exhibit higher oxidative activity than granulocytes. Such observation is not common since numerous studies show that granulocytes are usually cells that have the highest cellular activities. This result demonstrates the significant functional variability of hemocyte subpopulations. Moreover, our findings reveal that spawning period of Dreissena polymorpha was associated with an increase of hyalinocyte percentage in relation to low levels of biological activities in hemocytes. This reduction in hemocyte activity would reflect the important physiological changes associated with the spawning period of this invasive species known for its high reproductive potential.

Transcriptomic responses to low temperature stress in the Manila clam, Ruditapes philippinarum

The Manila clam, Ruditapes philippinarum, is an economically important shellfish in marine aquaculture, with a broad thermal tolerance. The ability to cope with cold stress is quite important for the survival of aquatic species under natural conditions. A cold-tolerant clam that can survive the winter at temperatures below 0 °C might extend our understanding of the mechanisms underlying the response to cold stress. In this study, the transcriptional response of the Manila clam to cold stress (-1 °C) was characterized using RNA sequencing. The transcriptomes of a cold-treatment (O) group of clams, which survived under cold stress, and the control group (OC2), which was not subjected to cold stress, were sequenced with the Illumina HiSeq platform. In all, 148,593 unigenes were generated. Compared with the unigene expression profile of the control group, 1760 unigenes were up regulated and 2147 unigenes were down regulated in the O group. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that signal transduction, mitochondrial metabolism, cellular component organization or biogenesis, and energy production processes were the most highly enriched pathways among the genes that were differentially expressed under cold stress. All these pathways could be assigned to the following biological functions in the cold-tolerant Manila clam: signal response to cold stress, antioxidant response, cell proliferation, and energy production.

Phagocytic activities of hemocytes from the deep-sea symbiotic mussels Bathymodiolus japonicus, B. platifrons, and B. septemdierum

Deep-sea mytilid mussels harbor symbiotic bacteria in their gill epithelial cells that are horizontally or environmentally transmitted to the next generation of hosts. To understand the immune defense system in deep-sea symbiotic mussels, we examined the hemocyte populations of the symbiotic Bathymodiolus mussel species Bathymodiolus japonicus, Bathymodiolus platifrons, and Bathymodiolus septemdierum, and characterized three types of hemocytes: agranulocytes (AGs), basophilic granulocytes (BGs), and eosinophilic granulocytes (EGs). Of these, the EG cells were the largest (diameter, 8.4-10.0 μm) and had eosinophilic cytoplasm with numerous eosinophilic granules (diameter, 0.8-1.2 μm). Meanwhile, the BGs were of medium size (diameter, 6.7-8.0 μm) and contained small basophilic granules (diameter, 0.3-0.4 μm) in basophilic cytoplasm, and the AGs, the smallest of the hemocytes (diameter, 4.8-6.0 μm), had basophilic cytoplasm lacking granules. A lectin binding assay revealed that concanavalin A bound to all three hemocyte types, while wheat germ agglutinin bound exclusively to EGs and BGs. The total hemocyte population densities within the hemolymph of all three Bathymodiolus mussel species were similar (8.4-13.3 × 10(5) cells/mL), and the percentages of circulating AGs, BGs, and EGs in the hemolymph of these organisms were 44.7-48.5%, 14.3-17.6%, and 34.3-41.0%, respectively. To analyze the functional differences between these hemocytes, the phagocytic activity and post-phagocytic phagosome-lysosome fusion events were analyzed in each cell type using a fluorescent Alexa Fluor(®) 488-conjugated Escherichia coli bioparticle and a LysoTracker(®) lysosomal marker, respectively. While the AGs exhibited no phagocytic activity, both types of granulocytes were phagocytic. Of the three hemocyte types, the EGs exhibited the highest level of phagocytic activity as well as rapid phagosome-lysosome fusion, which occurred within 2 h of incubation. Meanwhile, the BGs showed lower phagocytic activity and lower rates of phagosome-lysosome fusion than the EGs. These findings indicate that the two types of granulocyte play distinct roles in the defense system.

Development of histopathological indices in the digestive gland and gonad of mussels: integration with contamination levels and effects of confounding factors

Bivalve histopathology has become an important tool in aquatic toxicology, having been implemented in many biomonitoring programmes worldwide. However, there are various gaps in the knowledge of many sentinel organisms and the interference of confounding factors. This work aimed (i) to develop a detailed semi-quantitative histopathological index of the digestive gland and gonad of the Mytilus galloprovincialis mussel collected from five sites contaminated with distinct patterns of organic and inorganic toxicants along the Basque coast (SE Bay of Biscay) and (ii) to investigate whether seasonal variability and parasitosis act as confounding factors. A total of twenty-three histopathological alterations were analysed in the digestive gland and gonad following a weighed condition index approach. The alterations were integrated into a single value for a better understanding of the mussels' health status. The digestive gland was consistently more damaged than the gonad. Mussels from the most impacted sites endured the most significant deleterious effects showing inflammation-related alterations together with digestive tubule atrophy and necrosis. Neoplastic diseases were scarce, with only a few cases of fibromas (benign neoplasia). In contrast, in moderately or little impacted sites, contamination levels did not cause significant tissue damage. However, parasites contributed to overestimating the values of histopathological indices (i.e. more severe tissue damage) in mussels from little impacted sites, whilst the opposite occurred in mussels from highly polluted sites. Accordingly, inter-site differences were more pronounced in autumn when natural physiological responses of advanced maturation stages did not interfere in the histological response. In conclusion, although seasonal variability and parasitosis mask the response of histopathological indices, this biomonitoring approach may provide good sensitivity for assessing the health status of mussels if fluctuations of these confounding factors are considered.

Marteiliosis in mussels: a rare disease?

Among 1280 cultured and wild adult Mediterranean mussels, Mytilus galloprovincialis, collected over a 1-year surveillance period from the Slovene Adriatic Sea, 0.3% were histologically positive for the presence of Marteilia spp. The infection was concentrated in winter. Employing the molecular methods of PCR, cloning, DNA restriction and sequencing, only Marteilia refringens type M was detected in all the infected mussels. Although all life-cycle stages of M. refringens severely infected digestive glands, only sporadic disruption of epithelial cells of digestive tubules and focal destruction of digestive tubules were observed in the infected mussels. This was the first detection of M. refringens in M. galloprovincialis from the Slovene Adriatic Sea with the lowest prevalence reported to date. In addition, our results highlight the need for sequencing to complement the established PCR-RFLP analysis for correct parasite typing.

Future oceanic warming and acidification alter immune response and disease status in a commercial shellfish species, Mytilus edulis L

Increases in atmospheric carbon dioxide are leading to physical changes in marine environments including parallel decreases in ocean pH and increases in seawater temperature. This study examined the impacts of a six month exposure to combined decreased pH and increased temperature on the immune response and disease status in the blue mussel, Mytilus edulis L. Results provide the first confirmation that exposure to future acidification and warming conditions via aquarium-based simulation may have parallel implications for bivalve health. Collectively, the data suggests that temperature more than pH may be the key driver affecting immune response in M. edulis. Data also suggests that both increases in temperature and/or lowered pH conditions may lead to changes in parasite abundance and diversity, pathological conditions, and bacterial incidence in M. edulis. These results have implications for future management of shellfish under a predicted climate change scenario and future sustainability of shellfisheries. Examination of the combined effects of two stressors over an extended exposure period provides key preliminary data and thus, this work represents a unique and vital contribution to current research efforts towards a collective understanding of expected near-future impacts of climate change on marine environments.

Application of monoclonal antibody against granulocytes of scallop Chlamys farreri on granulocytes occurrence at different developmental stages and antigenic cross-reactivity of granulocytes in five other bivalve species

A monoclonal antibody (MAb) 6H7 raised specifically against granulocytes of scallop (Chlamys farreri) was employed to observe granulocyte occurrence successively in blastulae, gastrulae, trochophore larvae, D-shape larvae, umbo-veliger larvae and creeping larvae of C. farreri by immunohistochemistry assay contrasted with H&E stain using semi-thin sections. Moreover, the reactivity of the MAb with granulocytes of C. farreri, Bay scallop Argopecten irradians, Japanese scallop Patinopecten yessoensis, Blue mussel Mytilus edulis, Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum, was detected by immunofluorescence assay (IFA) with differential interference contrast and fluorescent microscopy and flow cytometric immunofluorescence assay (FCIFA). The results showed that positive signals were first observed at D-shape larval stage, about 28 h post fertilization, after that, umbo-veliger larvae exhibited the positive cells with a diameter of 3-5 μm distributed in velum, digestive gland and esophagus. Then in creeping larvae, the number of positive cells increased with average diameter of 5-7 μm, and widely distributed in foot, digestive gland, gills and adductor muscles. No positive signal was found in blastulae, gastrulae and trochophore larvae. The results of IFA and FCIFA showed MAb 6H7 reacted to granulocytes of C. farreri, A. irradians, P. yessoensis and C. gigas, and the positive percentage reactivity were 53 ± 2.5%, 15 ± 2.5%, 12 ± 2.1% and 19 ± 2.1%, respectively, however, no cross-reaction was detected in hemocytes of R. philippinarum and M. edulis.

Variability of the hemocyte parameters of cultivated mussel Mytilus galloprovincialis (Lmk 1819) in Sabaudia (Latina, Italy) coastal lagoon

The Sabaudia's lake consists of a protected coastal lagoon, located in the central Italy, historically characterized by recurrent mortality events of marine fauna during warmer months. A field study was monthly conducted on mussels Mytilus galloprovincialis cultivated inside the lagoon, measuring hemocyte parameters as total circulating count (THC), viability (HV), spreading and oxidative response to in vitro phagocytosis stimulation. A depression of the immune response was observed during the spring season, as indicated by higher values of hemocyte circularity and lower luminescence levels related to respiratory burst, also associated to modulation of THC and HV. The water temperature and the oxygen concentration appeared as the major environmental factors having influence on the phagocytosis activity. Therefore, the hemocyte variations have been intended as early danger signal to evaluate the immunodepression induced by the environmental stressors which could reveal in advance the development of critical situations for mussel survival.

Effect of a hemiuroid trematode on the hemocyte immune parameters of the cockle Anadara trapezia

When a trematode parasite penetrates a potential molluscan host, it has to circumvent the host's internal defense system. In molluscs, the primary effector cells of this system are the hemocytes which orchestrate many of the cellular and humoral immune functions. Survival of the parasite can occur only in the absence of a successful immune response, and continued development only if the host is physiologically suitable. This study investigated hemocytic response against asexual stages of a hemiuroid trematode by its host, the marine bivalve Anadara trapezia. Hemocyte characteristic (type, morphology) and function (mortality, phagocytosis and oxidative activity) were analyzed by flow cytometry in parasitized and non-parasitized cockles. A. trapezia possesses two types of hemocytes: amebocytes and erythrocytes. Analysis of histological section showed that there was no host hemocytic response around hemiuroid sporocysts. The infection induced a significant increase of the total circulating hemocytes with a higher proportion of erythrocytes relative to amebocytes, coupled with a lower phagocytosis rate and a statistically non-significant decrease of the intracellular oxidative activity. No significant differences were observed in hemocyte size and complexity, mortality, or phagocytic capacity. Our results indicate that in A. trapezia, hemiuroids modulate the immune response by increasing the number of circulating hemocytes and decreasing phagocytosis.

Immunological responses of the mangrove oysters Crassostrea gasar naturally infected by Perkinsus sp. in the Mamanguape Estuary, Paraíba state (Northeastern, Brazil)

Perkinsus genus includes protozoan parasites of marine mollusks, especially bivalves. In the last four years, this parasite has been detected in mangrove oysters Crassostrea rhizophorae and Crassostrea gasar from the Northeastern region of Brazil. Hemocytes are the key cells of the oyster immune system, being responsible for a variety of cellular and humoral reactions, such as phagocytosis, encapsulation and the release of several effector molecules that control the invasion and proliferation of microorganisms. In Brazil, there is little information on perkinsosis and none on the immune responses of native oysters' species against Perkinsus spp. The objective of this study was to determine the effects of natural infection by Perkinsus sp. on the immunological parameters of mangrove oysters C. gasar cultured in the Mamanguape River Estuary (Paraíba, Brazil). Adults oysters (N = 40/month) were sampled in December 2011, March, May, August and October 2012. Gills were removed and used to determine the presence and intensity of the Perkinsus sp. infection, according to a scale of four levels (1-4), using the Ray's fluid thioglycollate medium assay. Immunological parameters were measured in hemolymph samples by flow cytometry, including: total hemocyte count (THC), differential hemocyte count (DHC), cell mortality, phagocytic capacity, and production of Reactive Oxygen Species (ROS). The plasma was used to determine the hemagglutination activity. The results showed the occurrence of Perkinsus sp. with the highest mean prevalence (93.3%) seen so far in oyster populations in Brazil. Despite that, no oyster mortality was associated. In contrast, we observed an increase in hemocyte mortality and a suppression of two of the main defense mechanisms, phagocytosis and ROS production in infected oysters. The increase in the percentage of blast-like cells on the hemolymph, and the increase in THC in oysters heavily infected (at the maximum intensity, 4) suggest an induction of hemocytes proliferation. The immunological parameters varied over the studied months, which may be attributed to the dynamics of infection by Perkinsus sp. The results of the present study demonstrate that Perkinsus sp. has a deleterious effect on C. gasar immune system, mainly in high intensities, which likely renders oysters more susceptible to other pathogens and diseases.

Phagocytosis and respiratory burst activity of haemocytes from the ivory snail, Babylonia areolata

Haemocytes from the ivory snail, Babylonia areolata phagocytized Saccharomyces cerevisiae and Vibrio parahaemolyticus after 30 min. Haemocytes phagocytized V. parahaemolyticus at a greater rate than they phagocytized S. cerevisiae. The phagocytic rate (PP) of V. parahaemolyticus by granulocytes to was a little higher than that of S. cerevisiae. The phagocytic index (PI) of V. parahaemolyticus by granulocytes was significantly higher than that of S. cerevisiae. The same was true of hyalinocytes. The PP of granulocytes was significantly higher than that of hyalinocytes for each pathogen. No difference in PI was observed in granulocytes and hyalinocytes. Two defense mechanisms of B. areolata were quantified using flow cytometry. Haemocyte phagocytosis was quantified using fluorescent microbeads and respiratory burst activity was measured using H2O2 increases detected by 2', 7'-dichlorofluorescein diacetate. Both phagocytosis and respiratory burst activity of the haemocytes increased over time. After 90 min the phagocytic rate no longer increased. In the case of respiratory burst, the greatest increase in fluorescence occurred between 30 and 120 min, no further increase was seen after 120 min. These results showed unequivocally that a native (unstimulated) haemocyte oxidative burst was active in B. areolata. The aim of this study was to further the knowledge of immunology in gastropods.

Combined effects of carbonate alkalinity and pH on survival, growth and haemocyte parameters of the Venus clam Cyclina sinensis

Carbonate alkalinity (CA) and pH are considered to be two important stress factors that determine the response of aquatic animals to sudden transfers into saline-alkaline water. To evaluate the potential for aquaculture production of Venus clams (Cyclina sinensis) farmed in saline-alkaline water, the combined effects of CA (2.5 (control), 10.0, 20.0 and 40.0 meq/l) and pH (8.0 (control), 8.5, 9.0 and 9.5) on survival rate was monitored every day for 10 days. Length gain rate (LGR) and weight gain rate (WGR) were also monitored for two months, and total haemocyte count (THC), phagocytic rate (PR) and haemocyte mortality (HM) were measured for 3, 6, 12 and 24 days under the same water temperature (20 °C) and salinity (15‰) conditions. The results showed that survival rates in treatments of CA ≤ 20.0, combined with pH ≤ 9.0, were 100%. LGR and WGR in treatments of CA 2.5 & pH 8.0 (control), CA 2.5 & pH 8.5 and CA 10.0 & pH 8.0 exhibited the largest values (P > 0.05), while in other treatments, they showed a decreasing trend with an increase in either CA or pH or both (P < 0.05). Similarly, for THC, PR and HM, no significant differences were observed among the fast growth treatments during the entire experimental period (P > 0.05), however, in other treatments, they presented significant differences, especially on day 3 and 6 (P < 0.05), most notably with increases in CA or pH, but returned to control levels on day 12. In conclusion, in this study, a strong interaction between CA and pH was observed. Additionally, it was ascertained that the Venus clam C. sinensis can withstand the stress of CA 20.0 combined pH 9.0, although individuals grows slowly and may take approximately 12 days to recover to the unstressed condition.

Linking immune patterns and life history shows two distinct defense strategies in land snails (gastropoda, pulmonata)

Life history integration of the defense response was investigated at intra- and interspecific levels in land snails of the family Helicidae. Two hypotheses were tested: (i) fitness consequences of defense responses are closely related to life history traits such as size at maturity and life span; (ii) different pathways of the immune response based on "nonspecific" versus "specific" responses may reflect different defense options. Relevant immune responses to a challenge with E. coli were measured using the following variables: blood cell density, cellular or plasma antibacterial activity via reactive oxygen species (ROS) level, and bacterial growth inhibition. The results revealed that the largest snails did not exhibit the strongest immune response. Instead, body mass influenced the type of response in determining the appropriate strategy. Snails with a higher body mass at maturity had more robust plasma immune responses than snails with a lower mass, which had greater cell-mediated immune responses with a higher hemocyte density. In addition, ROS appeared also to be a stress mediator as attested by differences between sites and generations for the same species.

Influence of elevated temperatures on the immune response of abalone, Haliotis rubra

Elevated water temperature can act as a stressor impacting the immune responses of molluscs, potentially increasing their susceptibility to microbial infections. Abalone are commercially important marine molluscs that have recently experienced disease outbreaks caused by a herpesvirus and Vibrio bacteria. Sampling of wild-caught Haliotis rubra showed a significant correlation between water temperature and both antiviral and antibacterial activity, with higher activity in summer than in winter months. However, antibacterial activity was compromised in favour of antiviral activity as the water temperatures peaked in summer. A controlled laboratory experiment was then used to investigate several immune responses of H. rubra, including total haemocyte count (THC), stimulated superoxide anion production (SO), antiviral activity against a model herpesvirus, herpes simplex virus type 1 and antibacterial activity against a representative pathogenic bacterium, Vibrio anguillarum, over one week after raising water temperature from 18 to 21 or 24 °C. THC and SO increased at day 1 and then dropped back to control levels by days 3 and 7. By comparison, the humoural immune parameters showed a delayed response with antibacterial and antiviral activity significantly increasing on days 3 and 7, respectively. Consistent with the field study, antibacterial activity became significantly depressed after prolonged exposure to elevated temperatures. A principal components analysis on the combined immune parameters showed a negative correlation between antiviral and antibacterial activity. SO was positively correlated to THC and neither of these cellular parameters were correlated to the humoural antimicrobial activity. Overall, this study indicates that abalone may have more resilience to viruses than bacterial pathogens under conditions of elevated temperature, such as those predicted under future climate change scenarios.

Assessment of the effects of a marine urban outfall discharge on caged mussels using chemical and biomarker analysis

To assess the presence of endocrine disruptors in treated marine outfall discharges and their possible effects, mussels (Mytilus galloprovincialis) were caged in the environmental mixing zone of the outfall of the Santander sanitation system and in one control area. After 30, 60 and 90 days, samples were collected to perform chemical analyses (metals, anionic surfactants, alkylphenols, bisphenol A, phthalates and estrogenic hormones), biomarkers of general stress (lysosomal membrane stability-LMS, histopathology) and biomarkers of endocrine disruption (vitellogenin-like proteins and gonad index). There were no significant differences between outfall and control sites on contaminant levels, except for 4-tert-octylphenol which was higher in the outfall site. Bacteriological counts were higher in the outfall area. No relevant differences in biomarkers were detected between treated and control mussels. A significant reduction in LMS occurred in both groups after 90 days caging, indicating a stress situation possibly related to caging or to post-spawning reproductive state.

Immune parameters of QX-resistant and wild caught Saccostrea glomerata hemocytes in relation to Marteilia sydneyi infection

Sydney rock oysters (SRO) Saccostrea glomerata suffer mass mortalities during summer and autumn as a result of infection by a protozoan parasite Marteilia sydneyi (QX disease). Mass selected disease resistant (QXR) lines have been used with some success in affected estuaries in recent years, with resistance attributed to oxidative defense systems. However, the role of hemocytes in resistance to QX by SRO has not been fully explored. In the present study, fifty QXR and fifty wild caught (WC) oysters were collected from a lease at Pimpama River during a QX outbreak in January 2011. Hemocytes characteristics (type, morphology) and functions (mortality, phagocytosis and oxidative activity) from both oyster lines were analyzed by flow cytometry in the context of infection intensity and parasite viability (determined histologically). Amongst the QXR oysters, 20% were diseased containing viable parasite, 74% had killed M. sydneyi and 6% were uninfected. In contrast, 86% of WC oysters were diseased, 2% had killed M. sydneyi and 12% were healthy. Significant differences in hemocyte number and physiology between the two oyster lines were found (ANOVA). Phagocytosis rate and the mean oxidative activity per cell were similar between both oyster lines. Higher numbers of infiltrating and circulating hemocytes, higher percentage of circulating granulocytes, their higher size and complexity in QXR oysters, and the production of reactive oxygen species were associated with the ability to kill the parasite. High abundance of M. sydneyi in the digestive tubule epithelium of both oyster lines implied inability to kill the parasite at the beginning of the infection. However, QXR oysters had the ability to kill M. sydneyi at the stage of sporangiosorae in the epithelium of digestive tubules. The similar phagocytic ability of hemocytes from both oyster lines, the size of the parasite at this infection stage, and its localization suggested that encapsulation is likely to be the main process involved in the eradication of M. sydneyi by QXR oysters.

Age related properties of the Adriatic clam Chamelea gallina (L. 1758) hemocytes

The clam Chamelea gallina (L 1758) represents an important shellfish resource along Mediterranean coasts and its progressive depletion has been ascribed both to the overexploitation of stocks and to environmental or anthropic stressors. In this context, the investigation on immune parameters could represent a valid approach to measure the clam homeostasis condition and its possible influence on population dynamics. On this basis, the innate immune system, mainly represented by hemocyte phagocytosis, was investigated in organisms of different size. The results indicated a better phagocytic response in larger clams, strictly related to a greater concentration of granulocytes. A such variation in hemolymph composition appeared not dependent on environmental or endogenous factors, but rather on clam aging.

Non-specific defensive factors of the Pacific oyster Crassostrea gigas against infection with Marteilioides chungmuensis: a flow-cytometric study

In order to assess changes in the activity of immunecompetency present in Crassostrea gigas infected with Marteilioides chungmuensis (Protozoa), the total hemocyte counts (THC), hemocyte populations, hemocyte viability, and phagocytosis rate were measured in oysters using flow cytometry. THC were increased significantly in oysters infected with M. chungmuensis relative to the healthy appearing oysters (HAO) (P<0.05). Among the total hemocyte composition, granulocyte levels were significantly increased in infected oysters as compared with HAO (P<0.05). In addition, the hyalinocyte was reduced significantly (P<0.05). The hemocyte viability did not differ between infected oysters and HAO. However, the phagocytosis rate was significantly higher in infected oysters relative to HAO (P<0.05). The measurement of alterations in the activity of immunecompetency in oysters, which was conducted via flow cytometry in this study, might be a useful biomarker of the defense system for evaluating the effects of ovarian parasites of C. gigas.

Dual strategy for immune defense in the land snail Cornu aspersum (Gastropoda, Pulmonata)

Immune defenses have been shown to be heavily involved in the evolution of physiological trade-offs. In this study, we compared the internal defense systems in two subspecies of the land snail Cornu aspersum that exhibit contrasting life-history strategies. The "fast-living" Cornu aspersum subsp. aspersa is widespread throughout the world, especially in ecosystems disturbed by man, whereas natural populations of the giant Cornu aspersum subsp. maxima, characterized by a longer life span, are present only in north Africa. Snails were experimentally challenged with Escherichia coli; the measurements used to assess their internal defense for cell- and humoral-mediated immune responses were bacterial clearance, hemocyte density, reactive oxygen species (ROS) production, and plasma antibacterial activity. Both subspecies showed a similar ability to clear bacteria from their hemolymph; however, they varied in the robustness of different individual immune components. Cornu aspersum aspersa had higher ROS activity than did C. a. maxima and lower plasma bactericidal activity. These results suggest that ecological factors can sculpt the immune response. One interpretation is that shorter life span selects for immune defenses such as ROS that, although effective, can cause long-term damage. Such different immune patterns obviously entail various costs involved in the strong intraspecific variation of life-history trade-offs we previously observed. We also have to consider that such variation might be related to intraspecific differences in the relative strength of resistance and tolerance mechanisms.

Combined effects of temperature and salinity on functional responses of haemocytes and survival in air of the clam Ruditapes philippinarum

The combined effects of temperature and salinity on both immune responses and survival in air of the clam, Ruditapes philippinarum, were evaluated for the first time. The animals were kept for 7 days at three differing temperature (5 °C, 15 °C, 30 °C) and salinity values (18 psu, 28 psu, 38 psu), and effects of the resulting 9 experimental conditions on total haemocyte count (THC), Neutral Red uptake (NRU), haemolymph protein concentration, and lysozyme activity in both haemocyte lysate (HL) and cell-free haemolymph (CFH) were evaluated. The survival-in-air test was also performed. Two-way ANOVA analysis revealed that temperature influenced significantly THC and NRU, whereas salinity and temperature/salinity interaction affected NRU only. Temperature and salinity did not influence significantly HL and CFH lysozyme activity, as well as haemolymph total protein content. Survival-in-air test is widely used to evaluate general stress conditions in clams. In the present study, temperature and salinity were shown to influence the resistance to air exposure of R. philippinarum. The highest LT₅₀ (air exposure time resulting in 50% mortality) value was recorded in clams kept at 18 psu and 15 °C, whereas the lowest value was observed in clams kept at 28 psu and 30 °C. Overall, results obtained demonstrated that temperature and salinity can affect some functional responses of haemocytes from R. philippinarum, and suggested a better physiological condition for animals kept at 15 °C temperature and 18 psu salinity.

Insights into the innate immunity of the Mediterranean mussel Mytilus galloprovincialis

Background

Sessile bivalves of the genus Mytilus are suspension feeders relatively tolerant to a wide range of environmental changes, used as sentinels in ecotoxicological investigations and marketed worldwide as seafood. Mortality events caused by infective agents and parasites apparently occur less in mussels than in other bivalves but the molecular basis of such evidence is unknown. The arrangement of Mytibase, interactive catalogue of 7,112 transcripts of M. galloprovincialis, offered us the opportunity to look for gene sequences relevant to the host defences, in particular the innate immunity related genes.

Results

We have explored and described the Mytibase sequence clusters and singletons having a putative role in recognition, intracellular signalling, and neutralization of potential pathogens in M. galloprovincialis. Automatically assisted searches of protein signatures and manually cured sequence analysis confirmed the molecular diversity of recognition/effector molecules such as the antimicrobial peptides and many carbohydrate binding proteins. Molecular motifs identifying complement C1q, C-type lectins and fibrinogen-like transcripts emerged as the most abundant in the Mytibase collection whereas, conversely, sequence motifs denoting the regulatory cytokine MIF and cytokine-related transcripts represent singular and unexpected findings. Using a cross-search strategy, 1,820 putatively immune-related sequences were selected to design oligonucleotide probes and define a species-specific Immunochip (DNA microarray). The Immunochip performance was tested with hemolymph RNAs from mussels injected with Vibrio splendidus at 3 and 48 hours post-treatment. A total of 143 and 262 differentially expressed genes exemplify the early and late hemocyte response of the Vibrio-challenged mussels, respectively, with AMP trends confirmed by qPCR and clear modulation of interrelated signalling pathways.

Conclusions

The Mytibase collection is rich in gene transcripts modulated in response to antigenic stimuli and represents an interesting window for looking at the mussel immunome (transcriptomes mediating the mussel response to non-self or abnormal antigens). On this basis, we have defined a new microarray platform, a mussel Immunochip, as a flexible tool for the experimental validation of immune-candidate sequences, and tested its performance on Vibrio-activated mussel hemocytes. The microarray platform and related expression data can be regarded as a step forward in the study of the adaptive response of the Mytilus species to an evolving microbial world.

Expression of Mytilus immune genes in response to experimental challenges varied according to the site of collection

Mussels live in diverse coastal environments experience various physical, chemical and biological conditions, which they counteract with functional adjustments and heritable adaptive changes. In order to investigate possible differences in immune system capabilities, we analyzed by qPCR the expression levels of 4 immune genes (defensin, mytilin B, myticin B, lysozyme) and HSP70 in the Mediterranean mussel, Mytilus galloprovincialis collected in 3 European farming areas {Atlantic Ocean-Ría de Vigo-Spain (RV), French Mediterranean Gulf of Lion-Palavas-Prévost lagoon (PP) and Northern Adriatic Sea-Venice-Italy (VI)} in response to one injection of one of the 3 bacterial species (Vibrio splendidus LGP32, Vibrio anguillarum, Micrococcus lysodeikticus), and to heat shock or cold stress. We confirmed that the 5 genes are constitutively expressed in hemocytes, defensin being the less expressed, myticin B the highest. As suspected, the same gene resulted differently expressed according to mussel group, with the biggest difference being for HSP70 and lysozyme and lowest expression of all the 5 genes in mussels from RV. In addition, gene expression levels varied according to the challenge. Most frequent effect of bacterial injections was down-regulation, especially for mytilin B and myticin B. Heat shock enhanced transcript levels, particularly in mussels from RV, whereas cold stress had no effect. In situ hybridization of labelled probes on mussel hemocytes indicated that bacterial injections did not change the mRNA patterns of defensin and myticin B whereas mytilin B mRNA almost disappeared. In conclusion, these results demonstrated that constitutive level, nature and intensity of immune gene expression regulations strongly depended from mussel group, and support the concept of gene-environment interactions.

Influence of temperature, salinity and E. coli tissue content on immune gene expression in mussel: results from a 2005-2008 survey

Several bivalves, including mussels, suffered from mortalities particularly in summer. To look for the possible effect of environmental parameters on immune capacities, Mytilus galloprovincialis were collected monthly from August 2005 to July 2008 from the Palavas Laguna, French Mediterranean coast. Q-PCR was used to quantify the expression of three antimicrobial peptide genes (defensin, mytilin B and myticin B), in addition to lysozyme and HSP70. House keeping gene was 28S rRNA. Defensin, myticin B and lysozyme appeared more expressed in spring-summer than in winter. In contrast, HSP70 expression was higher in winter. Statistical studies using principal component analysis (PCA) and multiple regression models revealed positive influence of temperature on 28S rRNA, defensin, myticin B and lysozyme expressions, but not on mytilin B and HSP70. The positive influence was significant for defensin and lysozyme expression, but relationships cannot be quantified. Similarly, salinity appeared to influence defensin expression, but this relationship cannot be quantified neither. E. coli tissue content appeared without influence. Consequently, there was no clear relationship between environmental parameters and immune-related gene expressions, demonstrating anti-infectious capabilities cannot be evaluated using only the expression of such genes as markers.

In hemocytes from Mytilus galloprovincialis Lmk., treatment with corticotropin or growth factors conditions catecholamine release

The cells in charge of the innate immune response in the sea mussel Mytilus galloprovincialis Lmk. are the hemocytes, which have the capacity to release catecholamines when subjected to stressing conditions. Hemocytes were kept in culture before stimulation. That is, their behaviour was not studied immediately after extraction from the mollusc, as happens in most studies. This avoids the interference and variability caused by the conditions in which mussels may be when collected. This work describes the great variability found in the pattern of catecholamine release when the hemocytes are stimulated with either corticotropins or growth factors. Dopamine, adrenaline and noradrenaline release differs with each of the inducers assayed, with stimulation time and with the season of hemocyte collection. One of the results presented is particularly remarkable; such is the great amount of adrenaline and noradrenaline released to the medium when the hemocytes obtained in summer are stimulated with transforming growth factor-beta1 (TGF-beta1) for 60 min.

Development of mussel mRNA profiling: Can gene expression trends reveal coastal water pollution?

Marine bivalves of the genus Mytilus are intertidal filter-feeders commonly used as biosensors of coastal pollution. Mussels adjust their functions to ordinary environmental changes, e.g. temperature fluctuations and emersion-related hypoxia, and react to various contaminants, accumulated from the surrounding water and defining a potential health risk for sea-food consumers. Despite the increasing use of mussels in environmental monitoring, their genome and gene functions are largely unexplored. Hence, we started the systematic identification of expressed sequence tags and prepared a cDNA microarray of Mytilus galloprovincialis including 1714 mussel probes (76% singletons, approximately 50% putatively identified transcripts) plus unrelated controls. To assess the potential use of the gene set represented in MytArray 1.0, we tested different tissues and groups of mussels. The resulting data highlighted the transcriptional specificity of the mussel tissues. Further testing of the most responsive digestive gland allowed correct classification of mussels treated with mixtures of heavy metals or organic contaminants (expression changes of specific genes discriminated the two pollutant cocktails). Similar analyses made a distinction possible between mussels living in the Venice lagoon (Italy) at the petrochemical district and mussels close to the open sea. The suggestive presence of gene markers tracing organic contaminants more than heavy metals in mussels from the industrial district is consistent with reported trends of chemical contamination. Further study is necessary in order to understand how much gene expression profiles can disclose the signatures of pollutants in mussel cells and tissues. Nevertheless, the gene expression patterns described in this paper support a wider characterization of the mussel transcriptome and point to the development of novel environmental metrics.

Changes in circulating and tissue-infiltrating hemocyte parameters of European flat oysters, Ostrea edulis, naturally infected with Bonamia ostreae

We assayed European flat oyster, Ostrea edulis, hemocyte parameters, circulating and tissue-infiltrating hemocyte densities, circulating hemocyte type distribution and lysosomal enzyme contents, to possibly relate these hematological parameters to Bonamia ostreae infection. Circulating hemocyte densities were not statistically different between infected and uninfected oysters. In contrast, the number of tissue-infiltrating hemocytes increased with infection intensity suggesting a recruitment process at the site of infection and a possibility for cells to migrate from circulatory system to connective tissues. Lysosomal enzymes were localized mainly in granulocytes both infected and uninfected, and mean of alpha-naphtyl butyrate esterase activity decreased with increasing B. ostreae infection level. The main response observed was a change in hemocyte type distribution between uninfected and infected oysters and greater tissue-infiltrating hemocytes with increased infections. These results suggest that the decrease of circulating granulocytes, and, consequently of some cell enzyme activities may be related with B. ostreae infection.

Incidence of hemocytes and parasites in coastal populations of blue mussels (Mytilus edulis)--testing correlations with area, season, and distance to industrial plants

Blue mussel hemocytes (cells with immunoresponse activities) are suggested as indicators of anthropogenic contamination. We compared hemocyte numbers, granulocytoma (aggregated hemocytes), and parasites among populations of mussels from different areas of Skagerrak (a north and a south), seasons (summer and autumn), and impact levels (close or far from industrial activities). Seasonal hemocyte numbers were larger in the north compared to the south. Northern unimpacted populations had higher hemocyte numbers than populations close to industries, while no differences were found in the south. More uneven tissue distributions were found in populations far from industries in the north area and in populations close to industries in the south area. Parasites were more common in northern mussels than in southern, but no relationship to impact level was found. Mussels with granulocytoma, however, were found in all populations from the impacted sites while in none of the other populations suggesting granulocytoma as a possible indicator of industrial impact.

Effects of Bucephalus sp. (Trematoda: Bucephalidae) on Perna perna mussels from a culture station in Ratones Grande Island, Brazil

This study reports the prevalence of Bucephalus sp. in Perna perna populations from a culture station of southern Brazil and its effect on the mussel reproductive tissue and immune system. The prevalence of Bucephalus sp. in P. perna (n = 1871) was considered low (3.1%) and did not seasonally vary. Histological sections of the mantle of infected mussels revealed a marked (80%) reduction of the reproductive tissue that was severe even in mussels exhibiting a moderate infection degree. The total (THC) and differential (DHC) hemocyte counts were lower in infected mussels (3.9 x 10(6) hem/ml; granular hemocytes = 33%) as compared with non-infected animals (5.5 x 10(6) hem/ml; granular hemocytes = 40%). The plasma protein concentration did not vary upon infection. Hemocyte infiltration was significantly higher only in mussels with a very heavy infection degree. The parasite sporocysts were never seen encapsulated by the host hemocytes. Our results indicate that Bucephalus sp. promotes a severe castration in its host and apparently evades the mussel immune system.

Sample taking in invertebrate veterinary medicine

Invertebrates are important as pets of the 1990s but more so from economic, pest, and conservation perspectives. Since diagnosis by clinical examination is often taxing in these species, sample taking provides valuable insight into disease processes. Infection and parasitic diseases can be diagnosed by techniques from simple microscopy through to polymerase chain reaction technology. Cytology, hematology, and clinical chemistry, although not widely practiced, can provide critical baseline data in a disease investigation.