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.KEY WORDS: Bonamia sp. · Oyster culture · Ostrea puelchana · Argentina
Resale or republication not permitted without written consent of the publisherDis Aquat Org 63: [231][232][233][234][235] 2005 Aquaculture in Argentina is an emerging activity, as a new way to produce bivalve molluscs. A growing private interest concerning molluscan bivalve culture has stimulated research during the past century. Experimental farming of Mytilus edulis platensis, Aequipecten tehuelchus, and Ostrea puelchana has been carried out since 1980 (Pascual & Zampatti 1990, Zampatti 1990, Narvarte 1995, 2001.The native flat oyster Ostrea puelchana D'Orbigny is distributed from southern Brazil to northern Patagonia, Argentina (Castellanos 1957). Dense beds have been reported only in shallow subtidal waters of the NW San Matías Gulf (41 to 42°S, 63°30' to 65°W) ( Fig. 1) (Castellanos 1957). Research efforts concerning oyster culture have focused on spat collection and growout in the field (Pascual & Bocca 1987, Pascual & Zampatti 1990. Commercial flat oyster culture began in San Antonio Bay (Fig. 1), between March 1995 and December 1997, with the aim of exportation to the European Economic Community (EEC).Eighteen months after the beginning of the culture, the first abnormal mortality (33%) was recorded. After 31 months of culture, cumulative mortality was 80%, and 3 months later, when individuals reached marketable size, mortality was 95%. This prevented further commercial culture of Ostrea puelchana.The preliminary diagnosis, carried out on moribund oysters, indicated the presence of a 'Bonamia-like' haemocytic parasite which was the probable etiologic agent of the mortality (Kroeck 1997).The present study describes the haemocytic parasite that affected Ostrea puelchana. Histopathological analysis and evaluation of the parasitic prevalence were carried out during the course of commercial farming in San Antonio Bay.
MATERIALS AND METHODSSan Antonio Bay (40°47' S to 64°62'W) is northwest of the San Matías Gulf (Fig 1). Oysters used for commercial culture were collected on artificial collectors placed on the oyster ground of Las Grut...