Settlement of pediveligers of the Pacific oyster Crassostrea gigas on nitrocellulose membrane, plaster plate, GF/C filter paper, and glass, both as is and with extract from shells of conspecifics (oyster shell extract [OSE]) added to them, were investigated to select a suitable substrate for settlement assays with OSE. Furthermore, the effects of wheat germ agglutinin (WGA), soybean lectin (SBA), lentil lectin (LCA), and concanavalin A (ConA) on the settlement inducing activities of shell chips (SC) of conspecifics and OSE were investigated. Larvae of C. gigas did not settle on any of the substrates tested. When 50 mg SC equivalent (eq) OSE was added to each of these substrates, larvae settled on all substrates, but greatest settlements were on the GF/C filter papers. Settlement of C. gigas on SC and GF/C filter papers containing 100 mg SC eq OSE (OSE paper) decreased in the presence of WGA (0.5 µg/mL) and SBA (5 µg/mL) for SC, and 0.5 µg/mL for OSE paper, but increasing the concentration of SBA in both cases did not result in less settlement. Treating OSE paper with different concentrations of WGA for 2 h reduced C. gigas settlement on OSE paper, with settlement decreasing with the increase in WGA concentration. Treating larvae with 5 µg/mL WGA for 2 h also reduced larval settlement on OSE paper; but, at 50 µg/mL, larval settlement was not significantly different from the control group. Larval settlement was inhibited in the presence of N-acetyl-D-glucosamine (GlcNAc). Furthermore, larval settlement on OSE paper was not affected when OSE papers were treated with mixtures of 50 µg/mL WGA and GlcNAc. Shell chips and GF/C filter papers with OSE dyed with fluorescein isothiocyanate-conjugated WGA exhibited fluorescence under the UV field. Thus, a WGA-binding sugar chain of the glycoprotein in shells of conspecifics may mediate the settlement of C. gigas larvae on conspecifics.
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Vol. 33 • No. 2