Neurotransmitters induce larval settlement and juvenile growth of the sea cucumber, Holothuria scabra

The sea cucumber, Holothuria scabra, is a high-value economic animal in Thailand for local consumption and exportation. One major drawback in aquaculture of this species is that their larvae have low settlement and survival rates during the early developmental period. In the present study, we investigated the effects of various neurotransmitters, including GABA, dopamine (DA), L-DOPA, and monosodium glutamate (MSG) on larval settlement in both laboratory and practical models. In laboratory models, treatments of doliolaria with GABA or MSG, at a dose of 10⁻¹ mM for 72 h could induce larval settlement at about 90% and 93%, respectively, compared with the control group (about 20%) (P < 0.05), while treatments with DA or L-DOPA at a dose of 10⁻² mM for 12 h, were capable of inducing 100% settlement, compared with the control group (P < 0.05). In practical models, at day 37 after treatment, GABA or MSG significantly induced larvae to settle and survive at approximately 6% and 4%, respectively, while L-DOPA induced at about 3%, compared with the control group (about 0.2%) (P < 0.05). At day 37, all neurotransmitters-treated groups exhibited faster growth rates, while at 51 days, the growth rates of groups treated with DA, L-DOPA and MSG were faster, than the control group. GABA- and DA-treated groups also attained juvenile features earlier than MSG and L-DOPA-treated groups, and control groups. Taken together, this study shows significant effects of neurotransmitters on inducing settlement, increased metamorphosis and survival rates of the larvae of this sea cucumber, which could potentially be applied to enhance the production of this sea cucumber species.