Oyster Farming Cycle

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Oyster Farming Cycle

Each step is done in different spots. Their functions are determined by their geographical location, their depth, the bathymetry conditions (water depth) encountered, the risks of siltation, etc.

Refinement : (according to the interprofessionnal agreement of the CNC, in force since 1 January 2001 and the specifications of the PGI Marennes Oléron, in force since 2007)

Breeding – Collection : This is the collection of larva, immediately after reproduction.

Biology and oyster reproduction

Systématic :

The oyster is a bivalve mollusc (2 asymmetrical valves) lamellibranch ( lamellae gills), belonging to the filibranches category, the sub-category of anysomyaires and of the ostreidae family.

Biology :

Adult oysters reproduce sexually. Cupped oysters Crassostrea gigas are oviparous, meaning that the fertilisation of the eggs and the sperms occurs in the water influenced by the currents. They demonstrate alternative sexuality. They function as a male or as a female during a season and then change sex the following year. Some hermaphrodite (having both sexes simultaneously) subsist after the juvenile stage, but they are rare.

Reproduction :

In the month of May-June, oysters mature losing their winter fat reserves that will be replaced by the “milt”. At maturation the gonads swell with gametic products. This is due to the increasing changes in temperature and the salinity of the surrounding water.

As a result of an external shock, often a change in temperature, a mollusc begins to lay by emitting a pheromone (hormone), prompting its fellow oysters to do the same. Male gametes (sperm) and female (eggs) are fertilised in their natural environment, i.e. in the ocean. We talk about external fertilization.

Larval development:

24 to 48 hours after hatching, the larva begins to secrete its shell. It swims (pelagic). After 2 to 3 weeks, the foot appears, that’s when it seeks to cling to anything. It then transforms into a “small oyster”, it is called a spawn.


Around the 14th of July, oyster farmers place collectors (supports) at suitable spots: these supports are of different types. At Marennes-Oléron, they use plastic tubing, threaded and corded plastic plates, piles of slate, slate stakes, threaded and corded pieces of slates, “pleno” (rectangular supports filled with plastic blades).

Slate pieces and plastic tubes

The collectors are used as support for these small oysters which metamorphose when they cling to them.


18 months later, the spawns having grown on the collector, must be detached: the small oysters must be detached. They are called “grattis.”


It lasts 8 to 12 months. Two techniques are used:

“Flat” Concession: harrow and fishing with fork.

1. Either the grattis is directly sowed on the ground of the “flat” fields, and then fished with a fork 12 months later, to put the molluscs in farming. During this period, it is necessary to harrow the oysters so that they do not sink into the mud, they oxygenate well and grow into a nice round form.

2. Or the grattis is put directly in bags on “elevated” spots. The bags are placed on iron tables. They should be regularly turned and tapped to prevent the oysters from growing in length and sticking in the mesh.


It lasts 8 months.

The oysters are put in bags then placed on iron tables and turned at every tide.

The fact that the operation is done on foreshore (zones that uncovers at each low tide) renders the oysters very resistant out of water because the adductor muscle is well developed to retain water in the shell as long as possible. Hence, the Marennes-Oléron oysters stay fresh longer when closed and are of better quality.

At the end of summer, early autumn, the oysters are brought ashore, for maturation.


In order to get the best oysters on the market, EARL BOYARD performs the maturation process in claires. This gives them their fine terroir taste and the specific green colour typical of our region.


After sorting, the oysters are placed in claires. The density and maturation time should be abided by to be able to market under the Protected Geographical Marennes-Oléron Indication (PGI).

The flesh index should be respected, i.e. the quality of flesh according to the total weight of the oyster. It is determined by the interprofessional agreement of the CNC (Replacing the former AFNOR norm) Designation and classification of cupped oysters. Refer to “What products to choose“.

The objective of the maturation process is to improve the taste, texture and colour.

Required qualityMinimum duration of maturation
Density max/m²Index of quality (i)Particularity
Fines de clairesFrom 01/04 to 31/10: 2 weeks
From 01/11 to 31/03: 4 weeks
7 < i <10.5Preferably green
Fines de claires vertes Label RougeFrom 01/04 to 31/10: 2 weeks
From 01/11 to 31/03: 4 weeks
9 < i < 10.5Round, shuttered, fleshy, green. Sold to the consumer in their packaging
Spéciales de clairesFrom 01/04 to 31/10: 2 weeks
From 01/11 to 31/03: 4 weeks
i ≥10.5Round shuttered, fleshy
Pousses en claires Label Rouge4 months– 5/m²i ≥ 12Fattened in claire, very fleshy, characteristic taste of the terroir, not necessarily green


The greenness of the oyster is due to marennine. This is a green pigment produced by a phytoplankton algae, the navicule bleu, Haslea ostrearia. The marennine attaches to the gills when the oyster is submerged.


The final step of these four farming phases is the marketing of the product.

EARL BOYARD Roger et Sons ships all year round.

After this period of maturation, the oysters are washed, sorted and passed in the disgorging unit for 24 hours minimum. It remains to pack them in packages, weighed and counted before shipping to your address. At this instant the oyster is of the age of 4 to 5 years.