Xenomas in Crassostrea rhizophorae (Ostreidae) from Camamu Bay, Bahia, Brazil.

50 m 50 m This paper reports the occurrence of xenomas in the mangrove oyster Crassostrea rhizophorae (Guilding, 1828) gills. Xenomas are formed when intracellular parasites accumulate within host cells, causing hypertrophy of the cell and its nucleus. In fish, the xenomas are commonly caused by microsporidians (Matos et al., 2003), but in the oyster Crassostrea virginica (Gmelin) they are caused by ciliates, genus Sphenophrya (Bower et al., 1994; Winstead et al., 2004; Scarpa et al., 2006). In Brazil, Nascimento et al. (1986) observed such organisms in C. rhizophorae from Todos os Santos Bay (Bahia), but these authors didn’t make reference to xenoma formation. Thus, the present study is the first report of xenomas in C. rhizophorae. A total of 394 oysters were monthly collected between August 2006 and August 2007 in the Maraú Península estuary region (14° 06’ 55”-13° 59’ 92” S and 39° 02’ 83”-38° 59’ 92” W), Camamu Bay (Bahia, Brazil), on roots of the red mangrove Rhizophora mangle L.. The oysters were measured (dorso-ventral axis) and shucked. Meat fragments were kept in Davidson’s fixative solution (Shaw and Battle, 1957) for 24-30 hours, and then transferred to 70% ethanol. The material was processed for histology, with paraffin embedding, production of 7 μm thick sections and staining with Harris hematoxilin and Eosin (HE). The sections were examined with light microscopy. The water temperature ranged from 23.5 to 30 °C and the salinity from 15 to 35. The height of the oysters ranged from 2.7 to 10.2 cm and the xenomas occurred in animals measuring between 4.3 to 5.5 cm. The prevalence of xenomas was 2.53% (10/394). As reported in C. virginica (Bower et al., 1994; Winstead et al., 2004; Scarpa et al., 2006), the xenomas of C. rhizophorae were, very probably, caused by ciliates, genus Sphenophrya. The xenomas were formed in the gills epithelium (Figure 1). According to Bower et al. (1994), single Sphenophrya-like ciliates can also be observed attached on palps and possibly on the mantle of oysters. Unlike what has been reported in C. virginica (Scarpa et al., 2006), no macroscopic evi-