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Methods for the intermediate and final grow-out of hatchery-reared bay scallops are presented. Hatchery seed 5 mm in length can be efficiently grown to 20 mm in less than 2 months in a pumped raceway system at ambient temperature and phytoplankton levels between June and October. The maximum carrying capacity of the raceways at a seawater flow of 50 liters/min is about 5 liters of scallop biomass. At 10 liters of scallops per raceway phytoplankton availability is limiting. Growth is not affected by scallop densities as high as 1.8 liters/ m2. Raceway depth does not influence growth. Suspending small scallops in a net in the raceway does not improve growth. Seed scallops stocked at various densities in lantern nets deployed in Long Island Sound grow rapidly. Densities up to 1000/m2 seem feasible and this grow-out method may prove to be cost-effective.

Juvenile bay scallops (7.2-26.4 mm) were exposed for 72 h to different concentrations of un-ionized ammonia, nitrite, or nitrate. Using the Trimmed Spearman Karber method, 50% lethal concentrations (LC(50)) and 95% confidence limits were calculated individually for each. Un-ionized ammonia concentrations above 1.0 mg N-NH(3)/L resulted in 100% scallop mortality within 72 h. The 72-h LC(50) for un-ionized ammonia was calculated at 0.43 mg N/L. At nitrite concentrations of 800 mg N/L or higher 100% mortality was observed. The 72-h LC(50) for nitrite was calculated at 345 mg N/L. Nitrate was the least toxic, with 100% mortality observed at a concentration of 5000 mg N/L. The calculated nitrate 72-h LC(50) was 4453 mg N/L. Our results indicate that un-ionized ammonia is the most lethal nitrogenous waste component to bay scallops.

Scallops were suspended subtidally in pyramid-shaped (pearl) nets in Long Island Sound, Milford, Connecticut, USA to assess effects of density and temperature at deployment on growth and survival. Juveniles as small as 4 mm were grown at densities ranging from 250 to 15 000/m 2 . There was an inverse relationship between the size of the scallops and the density that affected growth. Scallops with a mean shell height of 16–17 mm exhibited no reduction in growth when held at densities as high as 7500/m 2 . Similarly, scallops with mean shell heights of 24 to 25 mm exhibited no reduction in growth when held at densities as high as 2500/m 2 . Growth of scallops held at biovolumes as high as 1.1 l/net was not affected substantially. Survival typically exceeded 80%, and was not affected by density. Different size groups of juvenile bay scallops were deployed at ambient temperatures of 5, 11.5 and 14 °C. Survival for all but one group was greater than 80%. Deploying scallops early in the season at temperatures lower than 14 °C appears to have no advantage relative to growth.