reproductive biology of this oyster and will help to elucidate the relationship between the disease and the host oyster. It can also allow for further comparisons with data taken from this population
whilst later extensively infected with Bonamia sp. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chilean oyster; Ostrea chilensis; Reproductive cycle; Breeding; Bonamia sp.
1. Introduction
The Chilean oyster, Ostrea chilensis, is a commercially important flat oyster that is Ž
. native to New Zealand and parts of South America Beu and Maxwell, 1990 . The
Ž species has been transferred around the world for aquaculture trials Utting and Spencer,
Fig. 1. Map of Foveaux Strait, New Zealand, showing the extent of the commercial beds of the Chilean oyster, Ž .
Ž . Ž .
O. chilensis, in 1970 and the four sampling sites for this study: A Saddle Bed, B West Bed, C Ruapuke Ž .
Bed, D East Bed.
. 1992 . The most extensive wild population and fishery for this oyster are spread over
1600 km
2
of Foveaux Strait in southern New Zealand, where oysters have been found in
y2
Ž . Ž
. densities up to 100 m
Fig. 1 Cranfield and Allen, 1977 . Over six years from 1985,
a protozoan parasite, Bonamia sp., destroyed most of the adult population in Foveaux Ž
. Strait Doonan et al., 1994; Hine and Jones, 1994 . This Bonamia species is thought to
be distinct from Bonamia ostreae, which has seriously affected the commercial produc- Ž
tion of the European flat oyster, O. edulis, in many parts of the world Elston et al., .
1986; Mialhe et al., 1988 . Bonamia species remain a significant threat to all fisheries and aquaculture of flat oysters and therefore a greater understanding of the relationship
Ž .
between the host and the parasite is needed Caceres-Martınez et al., 1995; Hine, 1996 .
´ ´
The pathogenesis of Bonamia sp. is closely related to the reproduction of O. Ž
. chilensis in Foveaux Strait Hine, 1991a, 1996 . Compared to other commercially
important oysters, such as O. edulis, the reproductive biology of the Chilean oyster is Ž
. poorly understood, especially in Foveaux Strait Jeffs and Creese, 1996 . Recent studies
have provided insights into the reproduction of O. chilensis in the warmer northern waters of New Zealand, but there are strong indications that the reproduction in these
populations is markedly different to that in colder southern areas, such as Foveaux Strait Ž
. Jeffs, 1998, 1999; Jeffs et al., 1996, 1997a,c . The recovery of stored samples of oysters
taken from Foveaux Strait in 1970–1971 provided a unique opportunity to describe the annual cycle of reproduction in this population 15 years prior to the mass mortalities
caused by Bonamia sp., which have greatly altered the population structure of these oysters. The aims of describing in detail the annual cycle of reproduction in this
population for the first time were to help elucidate the links between the reproductive biology of this oyster and Bonamia sp., and to provide an opportunity for comparisons
with descriptions of the reproductive biology of other populations of this oyster.
2. Materials and methods
