The effect of chemical cues on settlement behaviour of blacklip pearl oyster ( Pinctada margaritifera) larvae

Abstract

Inducing more rapid or greater degree of settlement of blacklip pearl oyster ( Pinctada margaritifera) larvae using chemical cues can significantly improve the commercial hatchery production of this valuable species. For this purpose, epinephrine, norepinephrine and γ-aminobutyric acid (GABA) were assessed at four concentrations (10 −2, 10 −3, 10 −4 and 10 −5 M), and in conjunction with plastic filaments for their ability to induce settlement of P. margaritifera larvae. In all concentrations tested, neither epinephrine nor norepinephrine had a significant effect on settlement and crawling behaviours of P. margaritifera larvae. Settlement of larvae occurred after 24 h in the presence of GABA at concentrations of 10 −3 and 10 −4 M; however, mortality was high (32%) at a concentration of 10 −3 M. Settlement and crawling behaviours were significantly greater ( P<0.05) and mortality significantly lower ( P<0.05) in the presence of plastic filaments alone than those exposed to GABA at a concentration of 10 −4 M. However, larvae in the presence of plastic filaments and exposed to GABA showed significantly reduced ( P<0.05) swimming behaviour and significantly greater ( P<0.05) crawling and settlement behaviours than larvae in the presence of GABA alone or plastic filaments alone. The presence of GABA increased settlement of P. margaritifera larvae onto plastic filaments from 14% in treatments with plastic filaments only, to 25% in the treatment with plastic filaments and GABA. The result of this study showed that GABA has a potential to increase the settlement rate of P. margaritifera larvae in hatcheries.