P.C. Southgate, A.C. Beer-1997
Journal of Shellfish Research, 16 (2) : 561-567 (from Current Contents)
Abstract:
This article reports on spawning induction and larval and early nursery culture of the blacklip pearl oyster Pinctada margaritifera (L.). Spawning was induced using thermal ''shock,'' where water temperature was manipulated from an overnight low of 22 degrees C to a high at spawning of 32-33 degrees C. Larvae were cultured in 500-L tanks in which the water was replaced every 3-4 days (static system) or in 500-L flow-through tanks in which 100% of the tank water was changed every 24 h. There was no significant difference in survival or growth of the larvae in static or flow-through tanks. Mean (+/-SE) anteroposterior shell length (APM) on Day 20, when larvae were transferred to settlement tanks, was 214.38 (+/-3.06) mu m and 217.52 (+/-2.93) mu m for static culture and flow-through culture tanks, respectively. Spat held in settlement tanks had a mean (+/-SE) dorsoventral shell height (DVH) of 1.38 (+/-0.03) mm at 43 days postfertilization when they were placed in plastic mesh trays and transferred to the sea. At 106 days of age, spat were removed from collectors and graded. The mean (+/-SE) DVH of 106-day-old spat was 11.2 (+/-2.7) mm; the largest individual had a DVH of 23 mm, whereas the smallest was less than 2 mm. At grading, 0.2, 8.9, and 67.3% of spat were retained on 15-, 10-, and 5-mm plastic mesh, respectively, and 23.6% fell through the 5-mm mesh. Growth of spat in plastic trays and pearl nets was assessed at densities of 10, 50, and 100 per tray and at densities of 20, 50, 100, 150, and 200 per net over a 19-wk growth trial. DVH was significantly greater in pearl oysters held in plastic trays at a density of 100 per tray (40.48 +/- 0.9 mm). Oysters held at this density also had the greatest APM (39.68 +/- 0.9 mm) and wet weight (7.44 +/- 0.4 g). Pearl oysters held in pearl nets showed the greatest DVH (39.22 +/- 0.6 mm), APM (38.36 +/- 0.6 mm), hinge length (34.47 +/- 0.5 mm), and wet weight (6.84 +/- 0.8 g) at the lowest density of SO per net. These values did not differ significantly from those of juveniles held at a density of 50 per net. Growth of juveniles held at densities of 20 and 50 per net was significantly greater than that of juveniles held at densities of 100, 150, and 200 per net. The presence of leatherjackets (Paramonacanthus japonicus) in trays and nets significantly affected growth rates of the spat.
(James Cook Univ. N. Queensland, Dept. Aquaculture, Townsville, QLD 4811, Australia)