Chemical induction of settlement behavior in larvae of the eastern oyster Crassostrea virginica (Gmelin)

• We treated competent C. virginica larvae with neuroactive chemicals.
• The larval responses to the chemicals were evaluated at a low salinity (9.6 ± 0.3).
• IBMX, 5-HT, l-DOPA, and NH3 all significantly increased larval settlement behavior.

Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, we placed competent C. virginica larvae in the microwells of tissue culture plates and treated them with select chemicals to identify those that were capable of inducing larvae to exhibit settlement behavior. These behavioral assays were recorded using video microscopy and the extension of the foot was the characteristic searching behavior that was quantified. The compounds γ-aminobutyric acid (10− 4 M) and acetylcholine chloride (10− 4 M) did not significantly increase the percentage of larvae exhibiting settlement behavior at a salinity of approximately 8.5 ± 0.2. As compared with a control, a significant increase in settlement behavior was induced at this salinity by treatment with 3-isobutyl-1-methylxanthine (10− 4 M), 5-hydroxytryptamine (10− 4 M), and l-3,4-dihydroxyphenylalanine (10− 4 M) as well as ammonia as a solution of 7.9 mM NH4Cl (pH = 8.0). These new findings differ from the results of similar studies involving other species in the genus Crassostrea and have the potential to improve setting efficiencies on a large scale by allowing hatchery personnel to trigger a controlled, synchronized settlement event of these larvae.