Effective use of plastic sheet as substrate in enhancing tropical oyster (Crassostrea iredalei Faustino) larvae settlement in the hatchery

Various methods were employed to exploit plastic sheet as substrate for enhancing tropical oyster (Crassostrea iredalei) larval settlement in the hatchery. Plastic texture (rough and smooth surfaces) and condition (with and without biofilm) showed a significant difference (P<0.05) on the larval setting rate. The highest setting rate was achieved for rough plastic without biofilm (37.6 +/- 2.2%) followed by rough plastic with biofilm (27.1 +/- 1.8%), smooth plastic with biofilm (22.0 +/- 2.1%) and the least recorded was on the control or smooth plastic without biofilm (11.0 +/- 1.2%), all of which differed significantly (P<0.05). Plastic substrate also appeared attractive to setting larvae by presoaking it in tissue extracts of several bivalve species. Plastic sheets presoaked in tissue extracts of C. iredalei and Crassostrea belcheri promoted better setting rates (28.3 +/- 3.9% and 26.1 +/- 5.5%, respectively) as compared to those soaked in tissue extracts from other bivalve species such as the green mussel, Perna viridis (15.7 +/- 1.4%) and the rock oyster, Saccostrea cucullata (12.9 +/- 3.6%). The setting rate on the control was also low (15.3 +/- 2.7%) and was not significantly different (P>0.05) from plastic with tissue extracts of the green mussel and the rock oyster. Exhalent water (used as media) from the above mentioned bivalve species were also found to increase oyster larval settlement on plastic substrate as compared to the control (without exhalent water). Higher setting rate was obtained for plastic with exhalent water from S. cucullata (48.9 +/- 3.5%) followed by C. belcheri (32.0 +/- 2.3%), P. viridis (30.4 +/- 4.3%) and C. iredalei (27.0 +/- 1.7%) which did not vary significantly (P>0.05), while lower setting rate was recorded for the control (18.9 +/- 5.9%). (C) 2002 Published by Elsevier Science B.V.