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A mortality episode (>90%) of triploid and diploid Pacific oysters Crassostrea gigascultured in Baja California Sur occurred during summer 2012, coinciding with a thermal anomaly, an algal bloom, and low oxygen values. To help explain the cause of the mortalities, histological analyses and molecular tests for specific pathogens (ostreid herpesvirus 1 [OsHV‐1] and Perkinsus marinus) were performed on oysters surviving at the end of the episode. Triploid oysters showed a high percentage of males (43%) and hermaphrodites (30%); 93% of these oysters were in the gonadic reabsorption stage, and in some cases, hemocytes completely filled the lumen of the gonadic follicles. Oysters presented large areas with severe hemocyte infiltration that extended toward the digestive gland. Diploid oysters showed similar gonad alterations. None of samples showed histological or molecular evidence of OsHV‐1 or P. marinus. Histological alterations can be related to physiological disorders caused by the mechanism driving summer mortality. This is the first case history of a summer mortality episode among Pacific oysters in Mexico.

The article discusses the identification of bacteria and burrowing worms associated with shell injuries on red abalone in Baja California, Mexico. Topics include the biological relationship between mud worms and parasites without harming the host, the unusual perforations over the shell and other organisms and the external shell lesions.

The Pacific geoduck Panopea generosa is distributed along the Pacific coast of the peninsula of Baja California, Mexico. Because of its high market value, this species has been under an intensive fishery pressure during the last few years, whereas its experimental aquaculture production is still developing. The fishery and culture practices point to the movement of clams as a risk factor for dispersion of symbionts, parasites, and diseases. Wild geoduck clams from fishery captures are sent to facilities that maintain clams alive, before marketing. Some of them show external abnormalities such as weakness and flaccidity, blisters, and darkening and thickening of the mantle surface and siphon. The objective of this study was to determinate if these abnormalities were related to parasites or diseases through conventional parasitological and histological analyses. The parasitological analysis showed two species of copepods, Pseudomyicola spinosus and a calanoid species in the mantle cavity and gills; additionally, a turbellarian species was also observed in the mantle cavity, none of these symbionts were related to tissue damage. The histological analysis showed that some weak-flaccid clams were in a postspawning condition. The dark and thick areas of the siphon and mantle suffered a dramatic transformation of the periostracum into a cavernous structure with numerous protozoans in different developmental stages. Fungi were occasionally observed in the external area of the periostracum. Unusual mortalities were reported by producers in clams with this abnormality. Rickettsia-like inclusions and trematodes were found in the digestive gland associated with limited damage to the host. The darkening and thickening of the siphon represent a major issue because of the negative appearance of the clams, which prevents its sale and is possibly related to the unusual mortality episodes. Detailed field and laboratory studies are needed to determine the origin of this pathology as well as its distribution and effect on the survival of the host. Moreover, field studies on the distribution, prevalence, and intensity of the other symbionts and parasites here detected are needed. These data constitute the first record for organisms associated with P. generosa in Mexico and a baseline for future studies. [ABSTRACT FROM AUTHOR]

The pleasure oyster Crassostrea corteziensisis collected and cultured in Nayarit on the Pacific coast of Mexico, and the improvement and promotion of its culture are seen as a possible source for the economic development of coastal populations. However, information about the parasite fauna of the pleasure oyster is almost completely lacking. A histopathological survey carried out in two estuaries, Boca del Camichín and Pozo Chino, revealed the presence of hypertrophied gametes, rickettsiales-like prokaryotes (RLPs), the protozoan Perkinsus marinus, a protozoan Nematopsissp., Ancistrocoma-like ciliates (ALCs), Sphenophrya-like ciliates, a turbellarian Urastomasp., and encysted crustaceans. In general, prevalence and intensity of parasites were similar in both localities except that ALCs and encysted crustaceans were more prevalent in Pozo Chino than in Boca del Camichín. Perkinsus marinusand RLPs seem to represent a more significant risk for the health of pleasure oysters than do the other parasites, and surveillance and control of these parasites are needed for the development of pleasure oyster culture.

The gonadal development by estimating the percentage of cell components of the mantle (MC) of cultured oysters (Crassostrea gigas) and mortality were studied in the Bahía Falsa, B. C. México from May 1996 to April 1997. Two localities, inner and outer zones of the Bay, were considered. Oysters were grouped in accordance with their position in the culture art, upper, middle, and lower level. Differences among the percentage of developing gametes (DG) and ripe gametes (RG) were according to the locality of the Bay and the position of the oysters in the culture art. In the outer locality, ripe gametes started to appear in February and reached their maximum proportion in May and June (around 60%). There was a trend of minor percentages of DG and RG in the lower level. Reproductive activity extends to November in the upper and middle levels. From September to January the no reproductive period was in curse. In the inner locality the percentage of ripe gametes also started to appear in February but their percentages were higher (around 80%) in May and June than in the outer locality. The reproductive activity ends in September. Percentage of vesicular cells (VC) increased from June to January. There was minor percentage of DG and RG in the lower level. There was no relationship between the gonadic cycle and mortality of oysters but it was with the level of the culture art, and there was an increase in mortality values in the lower than in the middle and upper levels of the culture art and a major mortality in the outer than in the inner studied localities. [ABSTRACT FROM AUTHOR]

The bay mussel, Mytilus galloprovincialis, and the California mussel, Mytilus californianus, are sympatric species in the Pacific coast of Baja California in northwest Mexico. To determine the reproductive cycle of both species in a coexistence area, a study of quantitative stereology was carried out from January to December 1995. M. californianus and M. galloprovincialis adults were collected from Mina del Fraile an exposed rocky shore and M. galloprovincialis adults were collected in a culture area a protected bay. In both species spawning organisms were found all year round. At population level, M. galloprovincialis had one major reproductive season from autumn to early spring in both sites. In late autumn, gonad follicles were full of ripe gametes and developing gametes and some spawning could occur. However, the spawning peak occurred in early winter. Minor spawning conditions were more frequent in M. galloprovincialis from the culture area than in M. galloprovincialis from the Mina del Fraile. These differences were presumably associated with the most stable environmental conditions in the culture area, which could also influence differences in percentage of storage cells found from spring to summer. The reproductive season of M. californianus took place from winter to summer. The major reproductive activity occurred in spring and the resting season took place during autumn. The reproductive season of M. californianus in the studied locality is from winter to summer, whereas the reproductive season of M. galloprovincialis occurs from autumn to early spring. [ABSTRACT FROM AUTHOR]

The culture of the Japanese oyster Crassostrea gigas is a successful commercial activity in Northwest Mexico. Since 1997, high mortality outbreaks have occurred in the area without apparent reasons. In this study we found gill erosions during clinical observations, hemocyte infiltration into the tissues at the histopathological level, and in some cases we detected the presence of giant polymorphic cells. In general, conditions mentioned above, including the presence of Trichodina sp. and especially the presence of giant polymorphic cells matches with the signs of the gill disease caused by an icosahedral DNA virus (Gill Necrosis Virus infection) first recorded in the Portuguese oyster Crassostrea angulata and in the Japanese oyster C. gigas in Europe. However, the Transmission Electron Microscopy (TEM) analysis of damaged tissues did not reveal the presence of viral particles. [ABSTRACT FROM AUTHOR]