Northern quahog, Mercenaria mercenaria, seed clam waste characterization study: precursor to a recirculating culture system design

The high demand and price of the northern quahog, Mercenaria mercenaria , enable this species to be an excellent commercial aquaculture candidate for coastal Georgia. The most economical method to grow clams is in the natural environment at controlled densities. Commercial nurseries grow small seed from the hatchery (1–2 mm) to a size suitable for planting in the field (8–10 mm). The pivotal role of the nursery phase to the success of bivalve mariculture has prompted research into improving nursery culture systems. Utilizing recirculation technology can contribute to the development and success of land-based nursery systems that offer higher survival and faster growth than field-based systems. This paper presents baseline excretion data that can be useful in the design of a recirculating system for culturing bivalve Mercenaria seed clams in a land-based system. The total ammonia nitrogen excretion rate based on a 24-h isolation period ranged from 20.0 to 89.4 μg NH 4 N g clam −1 day −1 for Mercenaria seed clams with a shell length ranging from 3.0 to 12.6 mm. The low ammonia production rate combined with the high ammonia tolerance limits of bivalves minimizes the need for a biofilter unit. The BOD 5 loading rate was highly variable and ranged from 0.05 to 0.32 mg l −1 -O 2 g clam −1 day −1 . For the seed clams that were less than 8 mm in shell length, the effluent total suspended solids concentration was three times greater than the larger size clams (10–12 mm shell length). Results indicated the importance of a solids removal mechanism to decrease the BOD 5 loading rate and reduce potential psuedofaeces production.