Oyster is name common to a number of different families of fresh-water bivalve molluscs which dwell in brackish or marine habitats.
A good number of oysters, though not all are in the superfamily named Ostreoidea.
Oysters generally have health benefits as they are rich in zinc which very important for the production of testosterone and maintenance of a healthy sperm.
Despite the fact that men have more testosterone than women, oysters also help and in maintaining and increasing the level of libido in women.
They are great dopamine (hormone responsible for increasing the level of libido in men and women) booster.
Various oysters are either eaten raw or cooked, in some instances, they are used as ornaments or pearls for decoration.
Scientific Classification
- Scientific Name: Ostreidae
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Bivalvia
- Subclass: Pteriomorphia
Types
There are different types of oysters, but we are going to consider only two major types, namely: Pearl oysters and True oysters.
Pearl Oysters
Pearl oysters are those type of oysters that secrete pearls, though some of these pearls are sometimes not valuable.
Two types of pearls, the natural and cultured pearls can be gotten from pearl oysters, although freshwater mussels which are also molluscs, also produce pearls which are valuable commercially.
Notably marine Pinctada maxima is the largest pearl-yielding Oyster, about the size of a dinner plate. Naturally, pearls are usually produced by pearl oysters through the covering of small incursive object with nacre. For years, the pesky object is under covering of nacre layers in order to become a pearl.
Different colors, types and shapes of pearls are contingent on the shape of the original irritant and the natural pigment of the nacre.
A pearl can be cultured by pearl farmers, simply by placing the nucleus inside the Oyster, this nucleus is usually of polished mussel shell. Oysters can produce a perfect pearl within 3 to 7 years.
True Pearls
True oysters belong to the Ostreidae family, and this family consist of edible oysters which primarily
belong to Crassostrea, Magallana, Ostrea, Ostreola, and Saccostrea. Eastern oyster, Pacific oyster, Sydney rock oyster etc are good examples.
Anatomy
Oysters are regarded as filter feeders, by beating their cilia, oysters are able to draw water in over their gills.
Trapped particles in the mucus of a gill, as well as plankton that are suspended, are transported to the mouth where these particles are eaten, digested and excreted as waste product (pseudo feces).
They mostly feed at a temperature 10°C and above. They can filter water up to 5 liters per hour. Surplus nutrients, algae and deposits can cause a body of water to become eutrophic and subject to eutrophication.
There also exist an interchange of gases across the mantles of oysters, in addition to their gills, which are line with thin-walled, small blood vessels.
A minute heart with three chambers, which lie beneath the adductor muscle is responsible for pumping colorless blood to all parts of the body.
Also, two kidneys which are located directly beneath the muscle does the job of expelling waste products from the blood. Oysters also have a nervous system which comprises of two pairs of nerve cords and three pairs of ganglia.
There are some oysters that have two reproductive systems (both sperm and eggs) which makes it technically possible for them to fertilize their own eggs, Example of these is the European and Olympia oyster.
The digestive organs are surrounded by gonads which are made up of branching tubules, sex cells and connective tissue. As soon as the female oyster become fertilized, she dispatches millions of eggs into the water.
The larvae of the Oyster then become suspended in the water column as veliger larvae for about three weeks, after six hours of developing into the larvae, before settling on a bed and then mature into sexual adulthood within a year.
Habitat and Behavior
Oysters, being a linchpin species provide habitat for several marine species. Species of oyster like Saccostrea and Crassostrea mainly dwell in the intertidal zone.
The corners between the hard surfaces of oyster shells provide shelter and a habitat for other small animals. The Oyster reefs are inhabited by barnacles, sea anemones etc.
The reef of an oyster can make the surface area of a flat bottom to increase by 50-fold. The mature shape of an oyster is contingent on the type of bottom to which it is attached originally, though it usually aligns itself with its flared, outer shell tipped upward. Usually, oysters attend a state of maturity within a year.
They breed as males by releasing sperm into the water, during the first year. Next, they breed as females by discharging eggs, this takes place as they advance in growth over the course of two or three years and also develop greater energy reserves.
Another type of oysters known as bay oysters mostly breed from the end of June until mid-August.
An increase in the temperature of water causes some oysters to breed, as a result, a female oyster can discharge 100 million eggs and above, yearly.
Spat are attached oyster larvae which are fertilized that settle in another oyster’s shell. These spats are 1inches long.
Is believed that oysters filter large amounts of water to feed and breathe (exchange O2 and CO2 with water), but they are not open permanently. They constantly close their valves to enter a dormant state, even if they are permanently immersed.
Their behavior follows very strict circatid and circadian rhythms according to the relative sun and moon positions. They have much longer closing periods during low tide than during spring tide.
Mangrove oyster which dwells in the tropics, from the family of Ostreidae grow best on mangrove root.
As Food
Oysters can either be eaten steamed, stewed, fried, broiled, baked or roasted with a variety of drinks to go with. In countries like Malaysia, fried oyster with egg and flour is a common delicacy.
Poached oyster can be served with cream roux on toast.
