![]() Crassostrea species, in contrast, are more typically inhabitants of estuaries in which they tolerate wide fluctuations in temperature, salinity, and turbidity. For instance, the European oyster, Ostrea edulis, grows in relatively cool, clear, water of high salinity (Yonge and Thompson, 1976). The ability of oysters to tolerate different environments is species specific. Oysters do not regulate their body temperature or the salinity of their body fluids thus, their metabolic activity is closely tied to the temperature of their surroundings, and the salt content of their blood is the same as that of the ambient water (Shumway, 1996). (1992) reviewed the literature on filtration rates for numerous marine bivalves and found that the relationship between filtration rate and size was similar for all species examined, including several oysters. Rates increase with size, although per unit weight, small oysters filter more water than do large individuals Filtration rates are a function of several environmental factors, including temperature, salinity, and suspended particulate concentration. Some particles, such as microalgae, are sent into the mouth others, such as sediment, are usually rejected and deposited as “pseudofeces” just outside the shell. Other gill cilia trap particles and funnel them toward the palps-large liplike structures, also covered with cilia that surround the mouth and on which particles are sorted. In an action called “pumping,” specialized cilia on the gill draw water into the shell cavity (Newell and Langdon, 1996). During feeding, they relax their single adductor muscle, allowing the two valves of the shell to open slightly. Oysters are plankton feeders they use their gills to filter microalgae and probably bacteria. The shape of the shell is typically dictated by environmental constraints, and they are capable of growing over or around adjacent objects, including other oysters. ![]() Oysters differ from other bivalves in having a highly irregular shell form. ![]() Most oyster species form the basis of local fisheries or aquaculture operations. Adults are intertidal and subtidal bottom dwellers found worldwide. Under the current systematic schema, most commercially important species are classified in three major genera: Ostrea, Saccostrea, and Crassostrea and a number of minor genera (Carriker and Gaffney, 1996). Oysters are members of the family Ostreacea, class Bivalvia, in the phylum Mollusca. ![]()
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