Occurrence of a rickettsia-like prokaryote in the small abalone, Haliotis diversicolor supertexta, cultured in Taiwan

In this study, we describe for the first time the detection of a rikettsia-like prokaryote (RLP) from cultured small abalone, Haliotis diversicolor supertexta, in Taiwan. The description of the microorganism was performed by histopathology and transmissible electron microscopy from lesions in the intestine. Results revealed the size and shape of RLP were different from those of Candidatus Xenohaliotis californiensis and molecular analysis based on 16S rDNA of Candidatus X. californiensis was unable to amplify a significant DNA segment from samples, which suggests that the RLP of the small abalone differs from that of C. X. californiensis of the abalone, H. cracherodii Leach. Introduction Withering syndrome (WS) has been catastrophic to wild populations of black abalone, Haliotis cracherodii, and the lesions of moribund abalone are characterized by severe foot muscle atrophy eventually leading to death (Antonio et al., 2000). A rickettsia-like prokaryote, Candidatus X. californiensis, which was identified as the etiological agent, produces lesions in the mucosal epithelium of the gastrointestinal tract (Friedman et al., 2000, Moore et al., 2001). The RLP was observed within cytoplasmic vacuoles of abalone gastrointestinal epithelial cells and the bacterial inclusions were usually situated apical to the nucleus of the host cells. The bacterium was found in cells of the postoesophagus, transport ducts of the digestive gland and, less frequently, the intestine. The predominantly observed inclusion was spherical to oblong in shape and contained homogeneous and densely packed bacteria that stained deeply purple with haematoxylin and eosin. No morulae were observed (Friedman et al., 2000). This disease is also responsible for heavy losses of white abalone H. sorensieni and red abalone, H. rufescens Swainson (Haaker et al., 1995; Moore et al., 2000). Pathogenesis of WS is complex and differs among host species (Friedman et al., 2000). However, these bacteria were also found in WS-symptomatic and -asymptomatic abalone (Tinajero et al., 2002). Rickettisa like organisms have also been described in cultured Haliotis discus hannai on the northern China (Guo et al., 1999). * Corresponding author’s E-mail: penheng@ntu.edu. tw Bull. Eur. Ass. Fish Pathol. , 28(2) 2008, 53 The small abalone, Haliotis diversicolor supertexta, is commercially important in Taiwan as a primary cultured species. Abalone farms are located in northern, eastern, and southern coastal areas of the island. In recent years, the appearance of symptoms of WS characterized by a shrunken appearance of the foot muscle and retracted visceral tissues have been noted in the ponds, and mortality has reported in some farms (Liu et al., 2000). This paper describes a RLP by histopathology and transmission electron microscopy in tissues of abalone H. diversicolor supertexta showing mortality in an abalone farm located in southern Taiwan. Materials and methods Sampling During a visit to an abalone farm in southern Taiwan in August 2004, 20 small abalone, 5-6 cm in shell length, were collected from the cages. This visit was part of an etiological study following mortality of spat abalone larvae in Taiwan. The foot muscle of all the abalone appeared shrunken, and visceral tissues were retracted. In the farm, abalone are cultured in land-based, flow-through tanks with forced air. Saltwater with a salinity of 33 ppt (parts per thousand) was pumped through pipes buried 1 m under the seabed, and the water temperature was approximately 24 °C. The abalone were fed with Gracilaria produced in ponds prior to introduction to