Effect of five chemical compounds on larval metamorphosis of the Cortez geoduck clam, Panopea globosa

Abstract

The clam, Panopea globosa, is one of two geoduck species intensively exploited in Mexico because of its high demand and commercial export value to Asian countries. Current efforts to develop successful seed production technology involve appropriate methods for improving the survival of larval and metamorphic stages. Several organic and inorganic chemicals have been successfully used to induce, synchronize or accelerate the settlement and/or metamorphosis of different molluscan species. In the present study the effect of 5 chemicals (serotonin, GABA, L-DOPA, epinephrine and KCl) on the metamorphosis of P. globosa larvae was tested at 3 different concentrations (10−6, 10−5 and 10−4M, or 1, 10 and 20mM in the case of KCl), with 3 different exposure periods (1.5, 6 and 24h). Percent metamorphosis and survival were evaluated after 30h. In each case, 3 metamorphic phases were documented (initial, intermediate and completed). Survival approached 100% after exposure to the different treatments, except with L-DOPA, where 80% of P. globosa larvae died after 24h exposure at the highest concentration (10−4M). The compounds GABA, L-DOPA and KCl failed to induce larval metamorphosis when compared to their respective controls. Serotonin rapidly triggered the initiation of metamorphosis, and the highest percent of metamorphosed larvae (87%±6.7 standard error) was observed in the combination of 6h exposure and 10−6M concentration. Epinephrine effects were slower than those of serotonin, yet the former also induced a high percent metamorphosis (>75%) after 6 to 24h exposure to a concentration of 10−4M or 10−6M. It is concluded that both serotonin and epinephrine can be potentially used to accelerate and synchronize the process of metamorphosis of P. globosa larvae.