Perkinsus marinus in pleasure oyster Crassostrea corteziensis from Nayarit, Pacific coast of México.

Culture of the pleasure oyster Crassostrea corteziensis is emerging as an alternative to the Pacific oyster (Crassostrea gigas) for oyster producers, who face severe mortalities since 1997 in Northwest México. For determining the health status of this species, we conducted a histopathological analysis of cultured populations from two estuaries in the Pacific coast of México. Macroscopical analysis revealed animals with transparent and retracted mantle. Histopathological analysis of these specimens showed tissue alterations and parasitic forms consistent with Perkinsus sp. infection. Stages of the parasite identified included tomont and trophozoites with an eccentric vacuole characteristic of Perkinsus spp. Pieces of tissues of infected oysters were incubated in Fluid Thioglycollate Medium (FTM) resulting in blue-black hypnospores after incubation. The identity of the parasite was confirmed by species specific PCR-based assay in DNA samples from oysters, tissue fractions from FTM cultures, and deparaffined samples with Perkinsus-like parasite detected by histology. Sequencing of positive amplified fragments (307bp) showed a sequence similar to Perkinsus marinus strain TXsc NTS ribosomal RNA gene (100% coverage and 98% identity, GenBank Accession No. AF497479.1) and to P. marinus, Genomic DNA, (100% coverage and 97% identity, GenBank Accession No. S78416.1). The prevalence of P. marinus varied from 1 to 5% in Boca del Camichín and from 1 to 6% in Pozo Chino. In general, the intensity of infection was moderate. The infection was observed in oysters from 31 to 110mm of shell length. This is the first record of P. marinus in oysters from the North America Pacific coast and the first record in C. corteziensis. The origin of this parasite in the area is unknown, but it may be associated to introductions of Crassostrea virginica from the East coast of United States of America or Gulf of México.

The marine mites Hyadesia sp. and Copidognathus sp. Associated with the mussel Mytilus galloprovincialis.

Two species of marine mites belonging to the families Hyadesiidae and Halacaridae, Hyadesia sp. and Copidognathus sp., respectively, were found associated with the mussel Mytilus galloprovincialis from Baja California in NW México. The first species was found inside the mussel gut with an intensity ranging from one to six mites per mussel and their prevalence was from 20.0 to 46.7%; this species was also found living free in the sediment at a density of 0.7 mite/100 ml. The second species was found on the mantle and gills of the host with an intensity ranging from one to three mites per host and their prevalence was from 3.3 to 6.7%; this species was abundant (4.5 mites/100 ml) and living free in the sediment around mussel clumps. Hyadesia sp. was found alive and attached in the gut of the mussel. A histological analysis revealed this species in the lumen of intestine surrounded by mucus and attached to the epithelial cells of the intestine, where some disorder of epithelial cells was associated. Moreover, this mite may be encapsulated by hemocytes inside the digestive diverticulum, the reproductive follicle, or the connective tissue surrounding the diverticulum. No damages to branches or gills resulting from the presence of Copidognathus sp. were observed. The results suggest that these mites are occasional invaders of mussels; however, as a result of this infestation, Hyadesia sp. may produce damage in the host's tissues. This is the first record of marine mites inside the gut, reproductive follicles, branches, and mantle of a marine bivalve.

The turbellarian urastoma cyprinae from edible mussels mytilus galloprovincialis and mytilus californianus in baja california, NW Mexico

The turbellarian Urastoma cyprinae (Graff, 1913) was found in the mantle cavity of Mytilus galloprovincialis Lamarck and Mytilus californianus Conrad, on the Pacific coast of Baja California NW Mexico. This is the first record of this turbellarian for bivalves from the Pacific coast of North America. In M. galloprovincialis from an exposed rocky shore, prevalence ranged from 10 to 87% and mean number of turbellarians per infested mussel was 1.9; in a culture area prevalence ranged from 57 to 100% and the mean number of turbellarians per infested mussel was 7.4. In the protected and polluted areas U. cyprinae was scarce or absent, prevalence ranging from 0 to 15% and the mean number of turbellarian per infested mussel being 0.07. The prevalence and the mean number of turbellarians per M. californianus in the exposed rocky shore ranged from 20 to 100% and 5.1, respectively. There were more worms in the larger mussels. Demibranches of M. galloprovincialis and M. californianus may be injured by the presence of turbellarians. An infiltration of hemocyte cells around the turbellarians was observed in both species and the blood sinuses in the infected area were engorged. Recorded damage was not related to a negative effect on the condition index of mussels. Copyright 1998 Academic Press.

Presence and Histopathological Effects of the Copepod Pseudomyicola spinosus in Mytilus galloprovincialis and Mytilus californianus

The copepod Pseudomyicola spinosus (Cyclopoidea, Myicolidae) was found in the mantle, gills, intestine, stomach, and connective tissue of the digestive gland of the blue mussel Mytilus galloprovincialis and the California mussel Mytilus californianus from Baja California, northwestern Mexico. The copepod can move from the mantle and gills to the digestive gland and vice versa. In M. galloprovincialis, copepod prevalence was 93% and its number ranged from 0 to 20 (mean, 5) in the mantle and gills and from 0 to 5 (mean, 1.1) in the digestive gland. In M. californianus, copepod prevalence was 43% and its number ranged from 0 to 2 (mean, 0.4) in the mantle and gills and from 0 to 1 (mean, 0.1) in the digestive gland. In the epithelium of the stomach and intestine of both mussel species studied, the appendages of P. spinosus may produce a loss of epithelial cells. Occasionally there was a light increase of hemocytes at the basal region of the stomach and intestinal epithelia where copepod was attached. In the lumen of the stomach and intestine copepods may be surrounded by mucus. P. spinosus was also found among the connective tissue of the digestive gland, apparently as a result of penetration through the wall of the stomach or other digestive organs. A granuloma-like structure engulfing the copepod in the connective tissue of the digestive gland was found. This is the first description of histopathological effects of P. spinosus in mussels.