Force recordings during escape responses by Placopecten magellanicus (Gmelin): Seasonal changes in the impact of handling stress

Handling stress coupled with air exposure reduced the contractile performance during escape responses of 2+ scallops, Placopecten magellanicus, modifying maximal and mean phasic force production, the number of phasic contractions and the minimal interval between phasic contractions as well as reducing maximal tonic force production and increasing the reliance upon tonic contractions. The impact of handling stress was mitigated in scallops studied in the fall (late October) relative to the summer (late June and late August), with smaller declines in performance for all parameters examined. Seasonal changes in escape response performance by unstressed scallops were few, with virtually no change in maximal or mean phasic force production, in the number of phasic contractions or in the minimal interval between phasic contractions. As the scallops sampled in October had lower condition indices than those sampled in summer, the reduced impact of handling stress was likely due to the lower air and water temperatures. This suggests that transfers of juvenile scallops during culture operations should be done during cooler periods. Force measurements during escape responses are a sensitive, but simple tool with which to assess the status of scallops as they clearly reveal the marked impact of handling stress as well as more subtle seasonal changes.