Generalities on oysters : biology, culture, environment ...

Being a typically natural product, appreciated since the antiquity, the oyster remains nowadays an exquisite dish.

What is an oyster ?

Classification

Kingdom :	Animal
Phylum :	Mollusc
Class :	Bivalve
Order :	Filibranchia
Suborder :	Anisomyaria
Family :	Ostreidae
Genus :	Pycnodonta, Crassostrea, Ostrea
Species :	Pycnodonta : hyotis, cohlear, numisma... Crassostrea : virginica, gigas, angulata, margaritacea, glomerata, rhizophorae, guyanensis, cucullata... Ostrea : edulis, sinuata, lurida, denselamellosa, chilensis, puelchana, stentina...

The pycnodonta genus gathers the bottom living oysters, they live in places that are always under the sea-level (until 2000m). Their shell is very spherical and made of vacuoles.
The Crassostrea are oysters that live in the tidal area of the coast (the part of the coast that is under water at high tide). The reproduction happens outside of the shell, when an ovule meets, by chance, a sperm cell.
The Ostrea genus lives in permanently submerged areas, or only occasionally dried areas, and it has a different breeding strategy : the fertilization happens inside the shell, and then the larvaes are thrown out to the outside.
Some species caused the arrival of a developed culture. And generally, we can say that the oyster consumption is universal, so much the repartition of the oyster cultures is regular all round the world.

Anatomy of the oyster

The oyster has got two valves (shells): it is a bivalve. It feeds out of plankton

schéma de l'anatomie de l'huître.

Thanks to Laure Robigo for her watercolour drawing

The function of the mantle : It is this slim veil of flesh that secures the growth and the development of the mollusc's shell. It also contributes to the forging of the nacre which recovers the inside of the shell.
The hinge hinge controls the opening of the oyster, while the adductor muscle keep it closed.
The gills have got two separate functions : the breathing and the supply of nutrients towards the mouth of the oyster.
If the oyster is well opened, it happens that we still can see its heart beating, which is situated just above the adductor muscle. The blood of the oyster is colourless.

The biotope of the oyster

Worldwide distribution of the oyster

We can find oysters more or less everywhere in the world, where there is the sea, generally in sheltered places (basins, ponds, lagoons...).
Indeed the various species have managed to adapt themselves to the various environments and biotopes of the world. However, salt is one of the elements that is quasi-indispensable for oysters. Some species are able to stay for 6 months in very low salinities, but generally low salinity is synonymous with death for the oyster. Every specie is adapted to a specific temperature, but even there, strong and sudden variations involve losses.
The oyster also requires a well oxygenated water and rich in food (plankton).

Distribution of the oyster farms in France

Map of the different production places in France
France produces two species of oysters : flat and round ones (Ostrea edulis and Crassostrea gigas). The flat oyster appears in small quantities almost everywhere on the Atlantic coast and also in the Mediterranean. As for the gigas, two places in France are the birthplaces of the gigas : Arcachon and Marennes-Oléron. This fact have led to the development of an interbassin trade. The oysters born in Arcachon are often grown elsewhere : either in Bretagne, in Normandy or at the Leucate lake. Indeed, these places are privileged places of cultures where the environment presents less difficulties for intensive breeding than in the collecting sites.
See also The problems.

Oyster farm of Marennes-Oléron

The Marennes-Oléron basin is a breeding and rearing place since a very long time, it reflects the characteristics of the natural habitat of the oysters in France. This place is sheltered by the Oleron island from the dominant winds (west). Strong tides discover natural benches which are easy to exploit. Moreover, three rivers: the Seudre, the Charente and the Gironde supply fresh water and guarantee an adequate salinity. However, this ideal environment caused the development of other cultures which are harming the oysters : the competitors.

Breeding of the oyster

Larves d'huîtres vues au microscope
Oyster larvaes at the stage of small little ones.

The sexuality of the oyster is particular. The oyster shows successive hermaphrodism : its sexual orientation changes year by year. At first, it will be a female and then, the second year, it will become a male. The oyster prepares its gametes in spring, as soon as the temperature exceeds the 10°C. Then, it waits until the water conditions are favourable for the emission of its gametes: a rather hot water (18°C at least) and a good salinity. It is often by a thundery or unsteady weather that the oysters releases their gametes. Then, it often happens that the sea itself becomes white so much the liberation of gametes is important. A single oyster rejects between 20 and 100 million ovules and even more spermatozoids. The gametes randomly meet, transported by marine currents in the marine environment. On the billion larvae thus formed, only 10% survive.

The different species

IThere are a lot of different species, according to the environments, but among those, we will only retain three essential ones :
Ostrea Edulis (flat oyster or belon in certain regions): the edulis is an ancient oyster : it is this one that the Romans consumed, it was indeed very abundant at that time. Of a restricted fertility, it is still bred in many areas throughout the world. Many people are researching it for its strong iodine taste.
Crassostrea angulata (Portuguese oyster) : If you speak about this oyster with certain French oyster producer, that will surely point out some memories to them, good or bad. This history is told to you here.
Crassostrea gigas (Japanese oyster): It is the most produced oyster and you will find it the most of the time on your plate in Europe.
We can quote among the other species : C. virginica (American oyster), cultivated in the USA and in Canada ; C. margaritacea (or rock'n'roll oyster) hot water specie, common in South Africa and Madagascar (Tuléar); C. rhizophorae (oyster fixed on the roots of the mangroves), O. sinuata or luteria (New Zealand oyster).

Properties of this mollusc

Benefits of the oyster

We need to sort the ideas that are often said on its real properties and the reality.

The oyster is a pure sea product and this is why it gathers many marine benefits. Thus, it has indisputable reconstituting and therapeutic qualities. In the past, it was prescribed as a medecine for the children who had a fragile health. It is indeed a source of vitamins, iron, copper and especially of iodine, that are essential elements for the organism. We can also say that some oysters have aphrodisiac virtues, but it is mostly the case for flat oysters, which are rare and expensive.

Nutritious properties table

General Elements	Approximate content of 100g oyster	Average Daily advised contribution	Vitamins	Approximate content of 100g raw oyster	Daily advised average contribution
Energy	65 Kcal	-------	A vitamin (retinol)	75 ug	1 mg
Water	83 g (about 80%)	-------	D vitamin	5 ug	10 ug
Proteins	8,9 g (between 7 and 10 %)	-------	E vitamin	0,85 mg
Glucides	4,7 g (between 1 and 5 %)	-------	C vitamin	5 mg	60 to 90 mg
Saturated fat acid	0,4 g	-------	B1vitamin (thiamin)	0,13 mg	1,3 to 1,5 mg
Monounsaturated fat acid	0,31 g	-------	B2 vitamin (riboflavin)	0,2 mg	1,5 to 2 mg
Polyunsaturated fat acid	0,38 g	-------	B6 vitamin (pyridoxin)	0,11 mg	2 to 2,25 mg
Cholesterol	50 mg	-------	B12 vitamin	16,5 ug	3 to 4 ug
Comestible proportion	0,11	-------	Pantothenic acid	0,6 mg	10 mg
Minerals
Sodium	280 mg		Magnesium	44 mg
Phosphorus	165 mg	350 mg	Potassium	220 mg
Calcium	92 mg	800 mg	Fer	6,3 mg	Man 10 mg Woman 18 mg
Iodize	0,073 mg ?	0,120 mg

Sources : L'encyclopédie des aliments (1996), Répertoire général des aliments (1995) et Alimentation et nutrition humaine (1992)

Ce qu'il faut retenir : les huîtres sont particulièrement riches en vitamine B12 et en fer. Et, d'une façon plus générale, des propriétés revitalisantes leurs sont reconnues. Mais tous ces chiffres ne doivent pas vous faire oublier que ce qui prime dans l'huître, c'est son goût.

About oysters