Despite continued interest and efforts spanning decades, scallop aquaculture along the West Coast of the United States remains a largely nonexistent industry. With the United States being one of the largest net importers of scallops globally, there remains a need to develop scallop aquaculture to meet this domestic demand. Purple Hinged Rock Scallops (Crassedoma gigantea) show a number of traits justifying their development as an aquaculture species including relatively large size, unique life history, and wide geographic range. Unlike other scallop aquaculture industries, the use of wild spat collection is not particularly feasible for the species due to their patchy distribution and unidentified areas for reliable wild spat collection. Reliable and efficient seed production is considered one of the major impediments to the development of the species for aquaculture.
While several hatchery protocols for C. gigantea are available, details regarding optimization of culture conditions are sparse and sometimes conflicting. This study investigated some of these aspects including tank water hydrodynamics and microalgae feeding density. One proposed impediment to C. gigantea larval survival is the kinetic stress due to aeration and water movement. Microalgae cell concentration is a known critical aspect of scallop aquaculture however the literature on the optimal feed concentration for C. gigantea larvae is relatively wide ranging with recommendations varying between 5-80K cells/mL. We conducted a series of range finding experiments to investigate the effect of aeration and feeding rate on larval growth and survival with the goal of determining an optimal range for rearing C. gigantea larvae.
The effects of aeration were tested using nine 135L concial bottom tanks that were fitted with airflow meters to regulate aeration rates between 0LPM and 3.2LPM. Scallop larvae shell length increased significantly over time as a function of increasing airflow and by proxy water movement in the tank (p < 0.001). We did not detect an upper threshold for aeration within our tested range. Our highest air flow treatment (3.2LPM) yielded the largest and fastest growing larvae over the 42-day experiment.
A second range-finding experiment was conducted in ten 135L concial bottom tanks to determine optimal microalgal feeding rates between 0 – 90K cells/mL. Feed concentrations were quantified and replenished to their prescribed densities daily over the course of the 36-day experiment. Larval growth and survival were significantly associated with feed density (p < 0.001). We found the optimal microalgae density to be between 3,000 – 15,000 cells/mL with lower concentrations (3,000 cells/mL) performing significantly better for survival over time and higher concentrations (15,000 cells/mL) significantly better for growth over time.
The results indicate that this species favors aeration rates and hydrokinetic stresses that may be detrimental to larvae of other species of scallops. Similarly, larvae perform better at microalgae densities lower than other commonly cultivated bivalves. Taken together these results show that C. gigantea respond markedly different to culture conditions of other farmed bivalves warranting further research and optimization of hatchery practices in order to generate reliable seed production to support industry development of the species.