EFFECTS OF MESH COVERS ON THE GROWTH AND SURVIVAL OF SILVER-LIP PEARLOYSTER (PINCTADA-MAXIMA, JAMESON) SPAT

Spat of the silver-lip (or gold-lip) pearl oyster, Pinctada maxima, we re re-settled onto PVC slats at a mean density of 340 per 100 cm(2). S pat had a mean (+/-s.e.) dorso-ventral shell height and antero-posteri or shell length of 1.2 +/- 0.3-mm and 1.8 +/- 0.5-mm, respectively. Th e PVC slats were either left exposed (control) or covered with a mesh sleeve of varying aperture sizes (0.75, 1.5 or 3.0-mm) before being tr ansferred to an ocean-based suspended nursery culture system. After tw o weeks of nursery culture, there was no significant difference (P > 0 .05) among the number of spat retained on the covered slats; however, all covered slats had significantly greater (P < 0.001) spat retention than the control which had fewer than 1 spat per 100 cm(2). Some of t he spat in the control treatment may have been eaten by box fish (Ostr aciidae) and file fish (Monacanthidae) which were observed pecking at the exposed PVC slats. Shell height and shell length increased signifi cantly(P < 0.05) with each increase in mesh size. The remaining spat o n the control slats were smaller than the mean size of the spat at the start of the trial although this difference was not significant (P > 0.05). This probably resulted from fish and other predators preferenti ally attacking the larger individuals. There was no advantage in using sleeves with a mesh size small enough to retain dislodged spat. The m ajority of dislodged spat in the 0.75-mm and 1.5-mm mesh sleeves peris hed when they fell into the corners of the sleeve whereas most dislodg ed individuals were small enough to fall through the 3.0-mm mesh sleev e. A 3.0-mm mesh is appropriate to house spat of the size used in this study. Smaller mesh sizes, while not affecting survival, fouled more rapidly and resulted in reduced spat growth. (C) 1998 Elsevier Science B.V. All rights reserved.