DESIGN AND MAINTENANCE OF A CLOSED ARTIFICIAL SEAWATER SYSTEM FOR LONG-TERM HOLDING OF BIVALVE SHELLFISH

To study the potential for transmission of Perkinsus karlssoni, an api complexan parasite, among bivalve hosts, a long-term laboratory-scale, closed, artificial seawater system for shellfish was designed. Specie s of shellfish utilised were as follows: bay scallops, Argopecten irra dians; blue mussels, Mytilus edulis; eastern oysters, Crassostrea virg inica; European oysters, Ostrea edulis; sea scallops, Placopecten mega llanicus; softshell clams, Mya arenaria; and quahaugs, Mercenaria merc enaria. All shellfish used were juveniles with shell heights of 10-25 mm. The design was duplicated for control and experimental systems wit h a combined population of 1600 individual shellfish. The maximum biom ass in each system was estimated at < 1 kg/m(3). Each system included six, 400 litre rectangular fibreglass tanks, a modular pump and filter unit (particle and activated carbon filters and ultra-violet sterilis ers), a biological filter and a refrigeration unit. The total volume o f water for each system was 2300 litres of artificial seawater (Instan t Ocean (R)). The mean water temperature of 22 degrees C was achieved by thermostat-controlled room temperature. Salinity was maintained bet ween 27 and 31 parts per thousand by addition of either freshwater or artificial seawater. Shellfish were fed daily a mixed diet of carboy-c ultured algae and spray-dried algae. Mean values for water quality par ameters in both systems were as follows: Nh(3) < 0.004 mg/litre; NO2- < 0.01 mg/litre; NO3- < 19.16 mg/litre; and pH 8.0-8.4. The system des ign was adequate in maintaining healthy bivalves for a period of 22 mo nths, with the exception of the sea scallops which succumbed to warm w ater. Mean monthly shellfish survival rates were 79.9-100% in the cont rol and 74.8-98.9% in the experimental system. A method of controlling water temperature other than via room temperature should reduce sligh t seasonal temperature fluctuations.