Force production during escape responses by Placopecten magellanicus is a sensitive indicator of handling stress: Comparison with adductor muscle adenylate energy charge and phosphoarginine levels

Scallops are quite vulnerable to handling and transport because they cannot completely close their valves. We examined how handling stress changed force production during escape responses of juvenile giant scallops, Placopecten magellanicus and compared these changes to those of adenylate energy charge (AEC) and phosphoarginine levels in the adductor muscle. We characterised force production 1) after the scallops were transported by boat in pearl nets from the culture site to the sorting area; 2) after the semi-mechanical sorting procedure; 3) after 3 h recuperation in holding tanks supplied with running seawater pumped in from the lagoon and 4) after 24 h recuperation in these tanks. Biochemical measurements were made at the first 3 stages. The patterns of force production during escape responses and muscle biochemistry showed clear parallels. The number and force of phasic contractions was markedly reduced by handling stress (transportation and sorting) but improved with recuperation in the holding tanks. Reliance on tonic contractions increased with handling stress but was reduced by recuperation. Phosphoarginine and adenylate levels in the adductor muscle confirmed that transport and handling were stressful and that 3 h in the holding tank allowed recuperation from this stress. The simplicity of measurements of force production during escape responses suggests this approach could be useful during planning of aquaculture operations. As these tests are non-destructive, they could also be used to monitor the status of scallops.