Effects of mesh covers on the growth and survival of silver-lip pearl oyster (Pinctada maxima, Jameson) spat

Spat of the silver-lip (or gold-lip) pearl oyster, Pinctada maxima, were re-settled onto PVC slats at a mean density of 340 per 100 cm². Spat had a mean (±s.e.) dorso-ventral shell height and antero-posterior shell length of 1.2±0.3-mm and 1.8±0.5-mm, respectively. The 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 transferred to an ocean-based suspended nursery culture system. After two 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 (P0.05). This probably resulted from fish and other predators preferentially attacking the larger individuals. There was no advantage in using sleeves with a mesh size small enough to retain dislodged spat. The majority of dislodged spat in the 0.75-mm and 1.5-mm mesh sleeves perished when they fell into the corners of the sleeve whereas most dislodged individuals were small enough to fall through the 3.0-mm mesh sleeve. 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