WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2022 35 ( C O N T I N U E D O N P A G E 3 6 ) being (e.g., pH, temperature, salinity) and a maintenance schedule become important. This study was done with adult milk conch Macrostrombus costatus as a proxy mollusk to the queen conch (Fig. 4). This allowed us to understand idiosyncrasies of the new outdoor seawater nursery recirculating aquaculture system. Likewise, the trial served to fine-tune system design to establish an adequate environment for successful juvenile queen conch rearing and development. Methods Amultilevel seawater nursery recirculating aquaculture system was built for rearing queen conch juveniles (Fig. 5). The system consists of six rectangular tanks in two stacks with three rectangular tanks per stack. Each fiberglass tank is 232 cm L × 51 cmW × 30 cm Hwith a surface area of 1.5 m2 and a volume of 270 L when filled to a water depth of 23 cm, as controlled by a 2-in PVC standpipe. Each tank independently drains through a standpipe into a sump (190 cm L × 77 cmW× 52 cmH) that holds a maximum volume of 360 L of seawater, approximately 25 percent of total system volume (1,613 L). Two submersible pumps (Danner Supreme Magnetic Drive Pump, Model MD92) were selected based on the overall tank system height (2.1 m), idealized flow rate (8 L/min per tank) and tank turnover rate (2×/hr). Each pump was placed in the sump and was designed to lift seawater from the sump to one stack of three tanks. Each tank has four trays (39 cm L × 46 cmW × 15 cmH) that each receive seawater through a spray-bar manifold, designed to provide circulation to avoid water stagnation (Fig. 6). Trays were built with 1.9-cm thick PVC panels for the walls and a window screen (diagonal 1.25-mm size opening mesh) attached to the bottom. Each tray contains approximately 20 mm of 1-3 mm aragonite sand (CaribSea, Inc.) used as a substrate for conch, physical filter to trap feed and biofilter for the system. To test the system, only the bottom two tanks were used for conch rearing. Although the systemwas designed for juvenile queen conch rearing, adult milk conch (n=24) were used to test the nursery system over a 10-wk period (8 December 2021 to 16 February 2022). Adult milk conch collected by Naguabo fishers from different locations on the south coast of Vieques, Puerto Rico were brought to the Naguabo Fishing Association. Once received, sex was determined by holding conch with their aperture facing down, which made it possible to see their reproductive structures as the animal slowly emerged from their shell. Males have a verge located high on the foot and females have a thin egg groove that extends the length of the foot (Fig. 7a, b). FIGURE 4. Measuring an adult milk conch Macrostrombus costatus that was part of the study (Photo: Megan Davis). FIGURE 5. Nursery recirculating aquaculture system used for the study and designed for growing queen conch juveniles (Photo: Chalier Dones-Ortiz). FIGURE 6. Each tank has four trays that each receive seawater through a spray-bar manifold (Photo: Chalier Dones-Ortiz).
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