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A regional shellfish hatchery for the Wider Caribbean – Assessing its feasibility and sustainability
transferred to larval tanks at densities of 10–15 larvae/ml for development into larvae. Rearing temperature for both species was 24 °C, salinity at 36 ppt (ambient) and no aeration was used in the first 24 hr of development. Trochophore larvae are formed within 24 hr of fertilization and D-larvae are developed within two days of fertilization (refer to Figure 1 for life stages). Food is supplemented to the larval culture at the start of Day-1 (trochophore stage) and from here on, larvae are fed daily a food ration consisting of live algal species, cultured on-site. Average yields of D-larvae for calico scallops determined per spawn, range from about 29–58 percent (Sarkis and Lovatelli, 2007). On the other hand, zigzag scallop yields are generally lower and are indicative of the greater sensitivity of this species to handling and bacterial contamination. The range of D-larvae obtained from of fertilized eggs was of about 1–49 percent per spawn over 4-years of operation at a Bermuda bivalve hatchery (see Sarkis and Lovatelli, 2007 for details on culture protocols for both species). Algal Culture The algal culture facility is a vital part of an aquaculture operation. Extreme care must be taken to ensure the production of healthy monocultures of selected algal species. Details on culturing algae are well documented and easily found in the literature. For specific techniques used in Bermuda for the scallop species, see Sarkis and Lovatelli (2007). Several types of algae were cultured as food for scallops namely, Isochrysis galbana, Chaetoceros gracilis, Tetraselmis chuii, Thalassiosira pseudonana. These were found sufficient to satisfy the growth and survival requirements of both scallop species to 2 mm spat. Food ration for Day 1 trochophore larvae was of 7 cells.µl-1, and was gradually increased to approximately 20 cells.µl-1 by the end of the larval life. This was determined to be the optimal ration for both species, based on experimental studies (Sarkis and Lovatelli, 2007). Ration was substantially increased for post-larvae once fixed, resulting in a daily ration Figure 2 of 220 cells.µl-1 for 2 mm spat. For extended nursery Collecting scallop larvae on sieves during rearing to 10mm, the use of commercially available water change in static tank system dry algae was necessary to supply increased volumes needed. Details on suppliers, volumes and species used are given in Sarkis and Lovatelli (2007).
PHOTO: M.M. HELM
Larval rearing Two types of larval systems were used in Bermuda: 1) 1 000 litre insulated tanks for static systems; and 2) 200 litre conical tanks for flow-through. The latter system proved less labour intensive with similar yields of pediveligers larvae. For a new facility, such a flow-through system is recommended (see Sarkis, Helm and Hohn, 2006 for details). Static rearing system Water change is conducted three times a week; at this time, larvae are collected on two sieves of differing mesh size, so that faster growing larvae are separated from the slower growing or dying larvae (Figure 2). Larvae are temporarily placed in small containers (10-litre buckets, while tanks are cleaned and re-filled with treated seawater (filtered twice to 1 µm and heated to 24 °C). Any assessment of larval