AB 11:53-63 (2010)  -  DOI: https://doi.org/10.3354/ab00293

ABSTRACT: Juvenile cultured northern quahogs or hard clams Mercenaria mercenaria can experience significant mortalities during their first winter, and cultured M. mercenaria var. notata clams, selected for fast growth, may be more susceptible. In the present study, selected and non-selected juvenile clams were overwintered off the north shore of Long Island, NY from November 2007 to June 2008 in order to understand the physiological, genetic, and environmental mechanisms contributing to overwinter mortality. Selected clams had a cumulative mortality of approximately 47% while the non-selected clams experienced 25% mortality. A decrease in carbohydrate reserves coincided with the mortality in both clam strains, but time-specific loss of carbohydrates was greater in the selected clams. Metabolic activity, as estimated by the activity of the electron transport system (ETS), was high during the winter-to-spring transition and was later reduced, presumably when clams became acclimated to the warmer temperature in May. Growth occurred after the observed reduction in ETS activity and was greater in the selected clams. This reduction in metabolic activity may allow for the balance of available energy to switch from maintenance to growth. These results support previous work suggesting a genetic component to overwinter mortality and demonstrate the significant effects of seasonal transitions on hard clam growth and energetics.

KEY WORDS: Hard clam · Mercenaria mercenaria var. notata · Overwinter mortality · Aquaculture · Biochemical composition · Metabolism · Growth · Energy