Reproductive condition of the pearl oyster, Pinctada
imbricata, Röding, in Port Stephens, New South Wales, Australia
W.A.
O'connor, N.F. Lawler-2004
Aquaculture Research, 35(4): 385-396
Abstract:
In
an investigation of the potential for pearl production in New South Wales
(NSW), Australia, changes in the physical and reproductive condition of the
pearl oyster, Pinctada imbricata, were monitored for over 2 years.
Using wild oysters gathered from close to the southern extent of the
species' range in Port Stephens, NSW, a series of macroscopic and
histological observations were made. Reproductive activity in P.
imbricata was greatest from late spring to early autumn with oysters in
poor reproductive condition during winter. Peaks in reproductive indices
occurred in November 1998, March 1999, December 1999 and April 2000. Four
indices of physiological condition were used: shell growth, byssal
attachment, mantle thickness and mucoprotien layer. With the exception of
the thickness and extent of the mucoprotein layer, these indices either
showed little variation or the variation that occurred was not related to
seasonal or reproductive changes. Changes in the mucoprotein layer were
correlated with water temperature and suggest that this layer is metabolized
during periods of high demand such as during gonadogenesis. Collectors
deployed at two sites in Port Stephens demonstrated that spatfall occurs
largely in the months of December and January following the spring and early
summer peaks in reproductive activity (November 1998 and December 1999).
Spatfall was not observed following the autumnal peaks (March 1999 and April
2000) in reproductive activity. Overall, reproductive patterns in P.
imbricata are poorly suited to spat supply in Port Stephens. Farmers
require spat in early spring (September) to allow maximum use of the
'growing' season (September-May). Reproductively capable oysters are not
available from the wild until September and quantity of natural spatfall is
too variable and occurs too late in the season (December-January). As a
result, oysters are being conditioned in the hatchery in July, spawned in
August and spat are supplied to farmers in mid September.
(NSW
Fisheries, Port Stephens Fisheries Centre, Taylors Beach, NSW 2316,
Australia. E-mail oconnorw@fisheries.nsw.gov.au)