Scallop aquaculture is the commercial activity of cultivating (farming) scallops until they reach a marketable size and can be sold as a consumer product. Wild juvenile scallops, or spat, were collected for growing in Japan as early as 1934. The first attempts to fully cultivate scallops in farm environments were not recorded until the 1950s and 1960s. Traditionally, fishing for wild scallops has been the preferred practice, since farming can be expensive. However worldwide declines in wild scallop populations have resulted in the growth of aquaculture. Globally the scallop aquaculture industry is now well established, with a reported annual production totalling over 1,200,000 metric tonnes from about 12 species. China and Japan account for about 90% of the reported production.
Cultured species There are varying degrees of aquaculture intensity used for different species of scallop. Therefore, cultured species can be divided into operations that are commercially well-established, those in the early commercial stages, those in development or experimental stages and those where potential for commercial farming has been expressed. Some species fall under multiple categories in different world regions.
Established commercial operations
Aequipecten opercularis (United Kingdom, northern France and Spain, Norway) Argopecten irradians (China) Sub species A. irradians irradians (eastern USA) Sub species A. irradians concentricus (eastern USA) Argopecten purpuratus (Chile) Chlamys farreri (China) Chlamys islandica (eastern USA) Chlamys nobilis (Japan, China) Mizuhopecten/Patinopecten yessoensis (eastern RussiaJapan, China, Western Canada [hybridized with Patinopecten caurinus]) Pecten fumatus (Australia) Pecten maximus (United Kingdom, northern France and Spain, Norway) Placopecten magellanicus (eastern USA)
Early commercial operations Argopecten ventricosus (Mexico) Chlamys islandica (Norway) Crassadoma gigantea (western North America)
Developmental or experimental
Aequipecten tehuelchus (Argentina) Aequipecten opercularis (Norway) Euvola ziczac (Venezuela) Nodipecten nodosus (Brazil, Venezuela) Patinopecten caurinus (western North America) Pecten maximus (China)
Species with potential Amusium balloti (Australia) Amusium pleuronectes (Philippines) Chlamys varia (northern Europe) Chlamys islandica (northern Europe) Euvola vogdesi (Mexico) Euvola ziczac (Brazil) Flexopecten flexuosus (northern Europe) Nodipecten subnodosus (Mexico)
Other species of note Attempts at cultivation of Chlamys hastate and Chlamys rubida in western North America have been halted due to the small size and slow growth of both species. Initial attempts made at cultivation of Pecten novazelandiae in New Zealand were hampered by large levels of fouling by mussels and by competition from a largely successful natural fishery.
Methods of culture There are a variety of aquaculture methods that are currently utilized for scallops. The effectiveness of particular methods depends largely on the species of scallop being farmed and the local environment.
Spat collection Collection of wild spat has historically been the most common way obtaining young scallops to seed aquaculture operations. There are a variety of ways in which spat can be collected. Most methods involve a series of mesh spat bags suspended in the water column on a line which is anchored to the seafloor. Spat bags are filled with a suitable cultch (usually filamentous fibers) onto which scallop larvae will settle. Here larvae will undergo metamorphosis into post-larvae (spat). Spat can then be collected and transferred to a farm site for on-growing. Spat collectors will be set in areas of high scallop productivity where spat numbers are naturally high. However, to establish where the most appropriate areas to collect spat are, trial collectors will often be laid at a variety of different sites. Well-funded farms can potentially set thousands of individual spat bags in collection trials.
Hatcheries Scallop hatcheries provide a number of advantages over traditional spat collection for supplying seed to aquaculture operations, most notably in selective breeding and genetic manipulation, as well as providing a regular supply of spat at a low price. While initial attempts to culture scallops in hatcheries were fraught with extremely low spawning and high larval mortality rates, a number of successful techniques have now been developed. One of the most important aspects of hatchery rearing is obtaining and maintaining broodstock. Broodstock must be conditioned so to stimulate gonad development leading up to spawning and much research has been devoted to identifying the best diets and water quality requirements for broodstock. Once broodstock have been conditioned, spawning can be induced. This is most commonly achieved by varying water temperature, increasing water circulation, or by an injection of serotonin (a neurotransmitter). Following spawning, scallop eggs will develop into the "D" larval (shelled) stage in 2 to 4 days post-fertilization. As larvae, they continue to grow and can be fed a variety of microalgal diets with mixed algal diets being reported as giving higher growth rates than single species diets. Settlement of larvae in hatcheries typically occurs between 35 and 45 days after fertilization of the scallop eggs when larvae are approximately 250 μm in size. Following settlement, the larvae undergo metamorphosis where they rearrange their body form to begin their life as a seafloor dwelling juvenile scallop. Mortality rates are often highest during metamorphosis as larvae go through a series of behavioral and anatomical changes such as loss of the velum (the larval feeding structure) and development of new filter-feeding mechanisms and gills. Post-settlement spat may be further grown in nursery tanks before being transferred to an on-growing system such as pearl nets.
Grow out stage There are two recognized systems for the grow out stage of scallops. These are hanging culture and bottom culture. Each has its own benefits and drawbacks in terms of cost, ease of handling and quality of the finished product. Enclosed culture systems still have not yet been fully developed in a commercial context and development continues in this area. Such a system would have large advantages over other forms of culture as tight control of feed and water parameters could be maintained.
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