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They are one of the best known and most widely cultivated marine animals.
Oysters are highly esteemed sea food and considered a delicacy in USA,
Europe, Japan.
Biology of Oysters
Oysters differ from other bivalves in having a highly irregular shell form. The shape
of the shell is typically dictated by environmental constraints, and they can grow
over or around adjacent objects, including other oysters (NRC 2004).
Oysters are filter feeders, drawing water in over their gills through the beating of
cilia. Suspended plankton and particles are trapped in the mucus of a gill, and from
there are transported to the mouth, where they are eaten, digested, and expelled as
faeces or pseudofeces. Oysters feed most actively at temperatures above 10 °C. An
oyster can filter up to 5 L of water per hour. While some oysters have two sexes
(European oyster and Olympia oyster), their reproductive organs contain both eggs
and sperm. Because of this, it is technically possible for an oyster to fertilize its own
eggs. The gonads surround the digestive organs, and are made up of sex cells,
branching tubules, and connective tissue (Wikipedia 2019h).
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. The ability of oysters to tolerate different environments is species specific. For instance, the
European oyster, Ostrea edulis, grows in relatively cool, clear, water of high salinity. Crassostrea species, in contrast, are more typically inhabitants of estuaries in
which they tolerate wide fluctuations in temperature, salinity, and turbidity.
Members of the genus Crassostrea shed their gametes directly into the water
where fertilization occurs, and larval life is spent entirely in the water column. In
contrast, fertilization, and partial larval development in Ostrea take place in the
interior of the oyster’s shell. Females release eggs within the shell cavity, and fertilization occurs when sperm shed by nearby male oysters get drawn into the female
cavity. The larvae develop partially among the female’s gill filaments, which turn
dark and become gritty as the larvae produce shells and become pigmented. The
female’s unpleasant appearance and texture at this time are the principal reason that
eating Ostrea species is avoided in the summer when reproduction occurs. The larvae of Ostrea species are eventually expelled from the female’s shell cavity and
complete their development in the water column. Oysters that are brooders produce
smaller numbers of offspring than nonbrooders (NRC 2004).
Oyster farming has become an increasingly important global aquaculture activity, accounting for the greatest proportion of molluscan aquaculture production. Out
of 100 known oysters species, only several are widely farmed. The most widely
cultured species are Crassostrea angulata and Ostrea edulis in Europe. Other species are C. iredalei (Philippines); C. gigas (Japan, Korea, West coast of the United
States and Canada); C. commercialis (Australia); C. brasiliana (East coast of
Southern South America); C. chilensis (West coast of South America);
3 Molluscan Shellfish
They are one of the best known and most widely cultivated marine animals.
Oysters are highly esteemed sea food and considered a delicacy in USA,
Europe, Japan.
Biology of Oysters
Oysters differ from other bivalves in having a highly irregular shell form. The shape
of the shell is typically dictated by environmental constraints, and they can grow
over or around adjacent objects, including other oysters (NRC 2004).
Oysters are filter feeders, drawing water in over their gills through the beating of
cilia. Suspended plankton and particles are trapped in the mucus of a gill, and from
there are transported to the mouth, where they are eaten, digested, and expelled as
faeces or pseudofeces. Oysters feed most actively at temperatures above 10 °C. An
oyster can filter up to 5 L of water per hour. While some oysters have two sexes
(European oyster and Olympia oyster), their reproductive organs contain both eggs
and sperm. Because of this, it is technically possible for an oyster to fertilize its own
eggs. The gonads surround the digestive organs, and are made up of sex cells,
branching tubules, and connective tissue (Wikipedia 2019h).
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. The ability of oysters to tolerate different environments is species specific. For instance, the
European oyster, Ostrea edulis, grows in relatively cool, clear, water of high salinity. Crassostrea species, in contrast, are more typically inhabitants of estuaries in
which they tolerate wide fluctuations in temperature, salinity, and turbidity.
Members of the genus Crassostrea shed their gametes directly into the water
where fertilization occurs, and larval life is spent entirely in the water column. In
contrast, fertilization, and partial larval development in Ostrea take place in the
interior of the oyster’s shell. Females release eggs within the shell cavity, and fertilization occurs when sperm shed by nearby male oysters get drawn into the female
cavity. The larvae develop partially among the female’s gill filaments, which turn
dark and become gritty as the larvae produce shells and become pigmented. The
female’s unpleasant appearance and texture at this time are the principal reason that
eating Ostrea species is avoided in the summer when reproduction occurs. The larvae of Ostrea species are eventually expelled from the female’s shell cavity and
complete their development in the water column. Oysters that are brooders produce
smaller numbers of offspring than nonbrooders (NRC 2004).
Oyster farming has become an increasingly important global aquaculture activity, accounting for the greatest proportion of molluscan aquaculture production. Out
of 100 known oysters species, only several are widely farmed. The most widely
cultured species are Crassostrea angulata and Ostrea edulis in Europe. Other species are C. iredalei (Philippines); C. gigas (Japan, Korea, West coast of the United
States and Canada); C. commercialis (Australia); C. brasiliana (East coast of
Southern South America); C. chilensis (West coast of South America);
3 Molluscan Shellfish