Larval-cleaning technique for increasing the survival rate of giant clam Tridacna crocea during the planktonic stage

Abstract

Giant clams are important species in tropical aquaculture. The larvae artificially hatched are often cleaned by running seawater containing the larvae through a coarse mesh, designed to catch contaminants larger than the larvae (e.g. fouling materials detached from adult clams); and then through a fine mesh, designed to catch the larvae and wash away smaller contaminants (e.g. bacteria). Such larval cleaning is assumed to improve the larval survival rate. We conducted experiments on how the cleaning improves the survival rate of larvae of the giant clam Tridacna crocea during the planktonic stage. The experiments revealed that larval cleaning improves the survival rate for larval densities of 0.3 to 9.8 indiv. mL⁻¹. The experiments suggested that the survival rate at 0.5 indiv. mL⁻¹, a typical larval density in hatcheries, would be 16.6% for the cleaned larvae, much higher than 1.4% for those not cleaned. Through larval cleaning, both bacteria and small T. crocea embryos showing maldevelopment were found to decrease in the water containing T. crocea larvae, which can explain in part the improved survival rate.