50 JUNE 2019 • WORLD AQUACULTURE • WWW.WAS.ORG In geoduck hatchery systems, broodstock collection, conditioning, spawning induction, knowledge of time to metamorphosis and settlement and algae culture techniques are like a steeplechase race with many obstacles that the hatchery operator must overcome to win. A fair amount of research has been done on geoduck reproductive biology, larvae and juveniles culture in North America (Marshall 2012, Ferreira-Arrieta et al. 2015, Liu et al. 2017) but very little of this research has been done in a proper pilot-scale or commercial-scale hatchery setting. Seed or spat for geoduck aquaculture development or fishery enhancement in North America are currently produced by only few dedicated small-scale hatcheries, including Taylor Shellfish (Washington State), Alutiiq Pride, OceansAlaska (Alaska), Manatee Holdings, Island Scallop (BC) and Laboratorio Oceanica (Baja California). Geoduck clams follow a simple annual reproductive cycle. In the natural environment, gametogenesis begins in September and spawning occurs from March to July but sperm or eggs can be found in the gonads of some adults during any time of the year (Sloan and Robinson 1984). For hatchery operation, adults (broodstock) are collected from wild sources from October through December. Prior to collecting broodstock, operators need to obtain a permit or certification from relevant regulatory agencies. In the USA, the fishery is jointly regulated by the Department of Natural Resources, Department of Fish and Wildlife and local Native American tribes. The Department of Fisheries and Oceans (DFO) is the main regulatory agency for the Canadian geoduck fishery and the Mexican fishery is managed by SAGARPA-CONAPESCA (Shamshak and King 2015). Broodstock Conditioning and Spawning After wild collection, broodstock need to be conditioned in a controlled environment, including optimum water temperature, salinity and feeding with cultured microalgae. To be used as a diet, microalgae has to meet various criteria, such as ease of culture, high nutritional value with the correct cell size, shape and digestible cell wall to make nutrients available for different life stages (Patil et al. 2005). In practice, hatchery operators use a combination of different algal species that provide balanced nutrition and good growth and survival. The most frequently used algal genera in geoduck hatcheries are Isochrysis, Chaetoceros, Phaeodactylum and Skeletonema (Fig. 5). Lack of experienced and skilled technicians or algologists hinders algae culture as well as quality diet production in geoduck hatchery systems in North America. In most hatcheries in North America, induction of geoduck spawning is conducted from November through early January. Spawning is triggered primarily by an increase in water temperature and the addition of cultured algae to the spawning tank. Broodstock are held in a spawning tank at 13-15 C and then water temperature is increased slightly while adding algal cells to the influent water. Generally, a male spawns first which then triggers spawning in other males and females. Usually relatively few females release eggs during a spawning event. Geoduck females have huge ovaries that contain 10-20 million eggs. Because they are partial spawners, a female will release about 1-2 million eggs during each spawning event (Goodwin and Pease 1989). Eggs and sperm are released into the water where fertilization occurs. However, spawning induction is only the beginning and hatchery operators need to provide a lot of attention and effort during the larval rearing period. Specialized training and observational skills are required to rear the resulting larvae successfully to obtain a sufficient number of juveniles. Larval Rearing Fertilized eggs hatch within 2-3 days, depending on rearing temperature. In North America, most shellfish hatchery operators FIGURE 6. Downwellers for larval geoduck settlement. FIGURE 5. Microalgae tanks for a geoduck hatchery operation.
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