Hatcheries traditionally rely on static culture for shellfish production. This method consists of holding larvae in batch tanks that are drained out two to four times a week. Though a reliable method, static culture is labor intensive, using a lot of resources such as algae and treated ambient water. Additionally, when water quality declines, facilities using batch culture are unable to efficiently reuse water, causing production to stall. As the demand for shellfish production continues to increase, innovative methods for culturing are necessary to support the industry and increase its resilience to environmental disturbances. With its efficient use of space and resources as well as buffering capacity against environmental variation, there is increasing interest in using RAS as a method of shellfish larval production .
A RAS is defined by a closed loop system where water is continuously treated and recycled for an extended period of time without water exchange. In a typical RAS, water from the culture tanks gets directed through a mechanical filter, UV sterilizer, foam fractionator, and biofilter before being directed back to the culture tanks. This method of shellfish culture has been demonstrated experimentally, though is yet to be adopted on a commercial scale.
The Shellfish Aquaculture Innovation Laboratory (SAIL) at the University of Maryland Center for Environmental Science’s Horn Point Laboratory recently refurbished three RAS that were previously used for finfish culture. Refurbishments included adding appropriate mechanical filters, biofilters, and charcoal filters. We then assessed the growt h and survival of Eastern oyster Crassostrea virginica larvae in the RAS in comparison to static culture. Numerous trials were conducted in both 2020 and 2021. In early trials, larvae were clear and would not grow in the RAS, suggesting starvation. Fluorometry assays revealed algae was quickly being removed by RAS filters and limiting larval access to algae. Food availability was subsequently improved by reducing the use of filters from 24/7 down to 2 hours every 5 days. Additional stressors considered were the effects of constant flow on developing larvae. This was assessed by culturing larvae within the RAS under static, constant high-flow, constant-low flow, and semi-continuous treatments. The results from these and other assays will be discussed. The a ssays at SAIL and other locations demonstrate culturing Crassostrea larvae in RAS is certainly possible but refining the culturing process so that it can support commercial-scale production will require more research.