Influence of exogenous chemicals on larval development and survival of the king scallop Pecten maximus (L.)

- Assessed effect of chemical agents on larval metamorphosis and larval survival
- Metamorphic response was low, and concentration-dependent
- KCl and L-DOPA at concentrations of 20mM and 10-6M, respectively, increased the rate of larval metamorphosis
- Effective KCl treatment reduced survival by 33%, whilst L-DOPA increased survival by 49%
- KCl promoted dissoconch growth and L-DOPA promoted gill development

The commercially important king scallop, Pecten maximus (L.), is the focus of ongoing research to optimise hatchery culture practices. At present, difficulties in the culture of this species are commonly associated with the transition from the larval to juvenile stages, with protracted metamorphosis, low development synchronicity and variable survival. The use of exogenously applied chemical agents, as demonstrated in other bivalve species, has been viewed as a means of resolving these issues. The present study evaluated the effects of the previously untested chemicals KCl, NH4Cl, acetylcholine chloride and GABA, in addition to the previously tested chemical l-DOPA, on the induction of larval metamorphosis and larval survival in P. maximus. A range of concentrations of each chemical, applied over a 48 hour period, were assessed. Larval metamorphic response, based upon the development of functioning gill filaments or secondary shell growth (dissoconch), was low and concentration-dependent. Larval survival was also concentration-dependent, with all chemicals becoming toxic to larvae at high test concentrations. Among the tested chemicals, KCl at 20 mM and l-DOPA at 10− 6M induced significantly (P < 0.05) higher rates of larval metamorphosis, which was improved by 208% and 128% respectively, compared to the controls after 7 days. However, whilst the KCl treatment was toxic, reducing survival by 33% compared to the control (P < 0.05), the l-DOPA treatment significantly increased survival by 49% compared to the control (P < 0.05). Furthermore, the influence of these two chemicals on larval development varied, with KCl promoting dissoconch growth and l-DOPA promoting gill development, suggesting that the pathways influenced by these two chemicals maybe different. In contrast, NH4Cl, acetylcholine chloride and GABA proved ineffective at inducing metamorphosis over the range of concentrations tested. The results of this study provide further evidence supporting the potential use of chemical agents, though further work is required to fully realise the ability to completely synchronise larval metamorphosis in P. maximus for hatchery application.Statement of relevanceInfluence of exogenous chemicals on larval development and survival of the king scallop Pecten maximus (L.)The results of this study provide important advances in our understanding and knowledge of the use of chemical agents in the commercially important bivalve Pecten maximus. This study has identified a new inductive chemical and highlighted considerations for future investigators.