Rhizocephalan infection in the Patagonian stone crab Danielethus patagonicus.

The system formed by a still-unidentified rhizocephalan infecting the Patagonian stone crab Danielethus (Platyxanthus) patagonicus (A. Milne-Edwards, 1879) was analyzed in northern Patagonia. Out of 3222 crabs sampled, mean prevalence of externae was 2.1%, while corrected mean prevalence based on observations of externae, scars or other indicators of infection was slightly higher (3.01%; N = 2100). Prevalence was higher in males (4.47%) than in females (1.44%). Parasitized males were morphologically feminized, while females showed no hyper-feminization. Although most parasitized crabs showed only 1 externa, 2 externae were observed in some individuals. The parasite externae were only present in intermediate-sized crabs (26.6-99.7 cm carapace width). While scanning electron microscopy images allowed detection of the 'smooth-surface-balloon' type of retinacula on the inner surface of the externae, typical of the Sacculinidae and Peltogastridae, the position of the mantle opening relative to the stalk, the receptacle location and the shape of the externae suggest that the parasite belongs to either the genus Sacculina or to the recently erected Parasacculina (Polyascidae).

Phylogenetics of Bonamia parasites based on small subunit and internal transcribed spacer region ribosomal DNA sequence data.

The genus Bonamia (Haplosporidia) includes economically significant oyster parasites. Described species were thought to have fairly circumscribed host and geographic ranges: B. ostreae infecting Ostrea edulis in Europe and North America, B. exitiosa infecting O. chilensis in New Zealand, and B. roughleyi infecting Saccostrea glomerata in Australia. The discovery of B. exitiosa-like parasites in new locations and the observation of a novel species, B. perspora, in non-commercial O. stentina altered this perception and prompted our wider evaluation of the global diversity of Bonamia parasites. Samples of 13 oyster species from 21 locations were screened for Bonamia spp. by PCR, and small subunit and internal transcribed spacer regions of Bonamia sp. ribosomal DNA were sequenced from PCR-positive individuals. Infections were confirmed histologically. Phylogenetic analyses using parsimony and Bayesian methods revealed one species, B. exitiosa, to be widely distributed, infecting 7 oyster species from Australia, New Zealand, Argentina, eastern and western USA, and Tunisia. More limited host and geographic distributions of B. ostreae and B. perspora were confirmed, but nothing genetically identifiable as B. roughleyi was found in Australia or elsewhere. Newly discovered diversity included a Bonamia sp. in Dendostrea sandvicensis from Hawaii, USA, that is basal to the other Bonamia species and a Bonamia sp. in O. edulis from Tomales Bay, California, USA, that is closely related to both B. exitiosa and the previously observed Bonamia sp. from O. chilensis in Chile.

Bonamiosis status in natural Ostrea puelchana beds in San Matías Gulf (Patagonia, Argentina), 14 years after an epizootic.

Between 1995 and 1996, Bonamia exitiosa caused an epizootic in San Matías Gulf, Argentina, that spread from a commercial culture site of Ostrea puelchana to natural beds located at the northeastern coast of the gulf. A mortality rate of 95% was registered in cultured oysters, and oysters from natural beds were also affected. The aims of this study were to assess the parasite prevalence in oyster beds and the demographic structure 14 yr after the epizootic. Two different oyster beds were studied during 2009 and 2010. Parasite prevalence was studied related to oyster aggregation, density, sex, and oyster size. Prevalence reached 35.3% at Las Grutas and 18.9% at Banco Reparo and was proportionally associated with density. Prevalence was also associated with the type of aggregation in Banco Reparo, where carrier oysters were more infected. Infection was independent of sex category, and infected oysters were larger than the non-infected ones. Oyster density decreased markedly compared to previous studies in both beds and mean sizes were lower, while prevalence doubled. Because of the persistence of the beds in this period, disease seems to control the population structure.

Gross signs and histopathology of Ostrea puelchana infected by a Bonamia exitiosa-like parasite (Haplosporidia).

Haplosporidian microcells belonging to the genus Bonamia parasitise various species of oysters around the world. In Argentina, Bonamia sp. was the causative agent of mass mortality among Ostrea puelchana cultured in San Antonio Bay (San Matías Gulf), and it was detected in natural beds inside San Matías Gulf. In order to describe the gross and histopathological signs caused by Bonamia sp. in O. puelchana, cultured and wild oysters were sampled and analysed by traditional techniques including heart imprints and histology. Cells of Bonamia sp. were observed in connective tissue, free or within haemocytes, in gills and around the digestive gland, stomach, intestine and gonad. Gross signs, histopathological alterations in O. puelchana, and Bonamia sp. cytological morphology resemble those reported for B. exitiosa. However, I propose to treat the Argentinean species as B. exitiosa-like until more molecular and ultrastructural studies are conducted to determine the correct taxonomy.

Occurrence of the haemocyte parasite Bonamia sp. in flat oysters Ostrea puelchana farmed in San Antonio Bay (Argentina).

Culture of native flat oysters Ostrea puelchana d'Orbigny in San Antonio Bay (San Matías Gulf, Argentina) began in 1995. After elevated mortality (33%) occurred in September 1996, 18 mo after immersion, histopathological analysis and evaluation of parasitic prevalence was carried out. In October 1997, after 31 mo of cultivation, cumulative mortality was 80%, and in December of the same year, when individuals reached marketable size, mortality was 95% and culture was discontinued. The present study describes the haemocytic parasitism that affected O. puelchana, and suggests that a Bonamia sp. was the etiological agent. This parasite should be considered as a different species from Bonamia sp. detected in Australia and New Zealand until more studies are made to determine the correct taxonomy. This work constitutes the first record of this haemocyte parasite in flat oysters from the Argentinean coast.