Oysters

Oysters, of the Ostreidae family, have a very ancient history. To prove that we have an incredible discovery: a rare specimen containing an ancient pearl, dating back at least 10 million years.

The Chinese were the first to farm this type of mollusk, which was immediately appreciated by the ancient Greeks, who used it in daily life. At the time, oyster shells were even used for voting purposes. Oysters lost their relevance during the Middle Ages, but their value was rediscovered in the Renaissance.

It was Napoleon himself who, in 1853, established a true set of rules for sea fishing, in order to protect this species. From then on, oysters have become one of the most highly appreciated delicacies, especially among international chefs, who include them in their daily menus as a magical ingredient in many gourmet recipes.

Oysters: morphological and biological characteristics

Oysters are bivalve mollusks, with an external shell made of two valves that vary in shape:

The right valve (the upper one) has a generally flat shape and slight serrations (often due to constant exposure to tides) made of horny material (conchiolin);
The left valve, on the other hand, has a more or less deep cavity, resembling the shape of a spoon;
The inner surface of both valves contains the adductor muscle.

The hinge is toothless. As for biological features, oysters belong to a family of species that live in shallow marine waters in various parts of the world. One particularly interesting aspect concerns their sex: oysters are often born male or female but can change over time, alternating between male and female phases (hermaphroditic oysters).

Oysters: nutritional and health benefits

Oysters boast tremendous health benefits, which are closely tied to their nutritional profile. Not only do they offer a unique and exquisite taste, but they are also extremely good for you, as they contain minerals that are essential for the proper functioning of the body. Just think that they’re rich in zinc, calcium, sodium, potassium, phosphorus, iron and several B-group vitamins. According to Humanitas, the nutritional values per 100 grams of oysters are as follows:

10.2 g of protein
0.9 g of fat
5.4 g of carbohydrates
69 Kcal

The calcium and phosphorus content is essential for healthy bones and teeth, helping to strengthen and energize the muscular system. The presence of iron is beneficial for connective tissues and the production of specific hormones, as it’s a key component of hemoglobin.

Omega-3 is widely known for its many health benefits: it has a positive effect on heart, bones and brain, it offers powerful anti-inflammatory action and its supplementation is essential in the treatment of cancer-related conditions. Zinc, on the other hand, helps strengthen our immune system, protecting us from potential bacterial infections. In short, oysters are a true wellness booster!

Types of oysters: main European species

Among the main European oyster species, Crassostrea gigas undoubtedly stands out. Raise your hand if you haven’t heard of it at least once: many oyster varieties belong to this species, also known as the Pacific oyster or cupped oyster.

We’ll also take a closer look at Crassostrea virginica, Ostrea edulis and Saccostrea cuccullata, exploring the specific features that distinguish one from another. Each oyster species has its own unique characteristics, benefits, and traits that are worth keeping in mind when making a purchase. Let’s start with the first one!

Concave Oyster

Crassostrea gigas

FAO Name

OYG

Length

Maximum 16 cm

Distinctive Characters

One of the most distinctive traits is its elongated shape (the oyster is significantly taller than wide). On the surface, you can spot concentric, layered growth lines. The adductor muscle is found on the inner side of one of the two valves, it has an oval shape and is located closer to the central edge of the valve. The two valves are joined by an irregular, wavy line.

Coloring

The outer shell is mostly gray, with radial ribs in brownish or purplish tones. The inner surface is white.

Diffusion

Mediterranean Sea – especially in the Adriatic, French and Spanish coasts;

Eastern Atlantic – especially in the French coasts, British Isles, the Netherlands and Morocco;

Indo-Pacific – originally native to Japanese waters (still considered a highly prized product today);

Indian Ocean – waters around Mauritius;

Pacific Ocean – Hawaii, the Philippines, Thailand, Australia, Tasmania, and New Zealand. On the eastern side: Chile, Costa Rica, from British Columbia to California.

Meats

Tasty and meaty, they can be enjoyed raw or preserved.

Types

Ostrea Regal selection or

Oyster Gillardeau

Cristalda Italian Oyster

Oyster Boudeuse by David Hervé

Oyster Utah Beach

Oyster Tsarskaya

Oyster Special Sentinelles

Oyster Royal by David Hervé

Oyster Fine de Claire

Oyster Desse Blanche

Oyster La Pleaide Poget

Oyster St. Michael

Oyster Mater of Sardinia

Oyster Fine de Claire Verte

Tarbouriech France

Noblesse and Divina

Oyster Marie Morganes

Tarbouriech Italy

Peter Pan Oyster

Ideal Oyster

American Oyster

Crassostrea virginica

FAO Name

CNR

Length

Maximum 22 cm

Distinctive Characters

This species has an oval shape (again, taller than wider). On the surface, you can see growth lines and some radial ribs. The lower valve takes on a long, spoon-like shape. The adductor muscle, located on the inner side of one of the two valves, is oval and positioned closer to the central edge of the valve than to the hinge here as well. The two valves feature broad, irregular undulations.

Coloring

The outer shell is generally gray to brownish in color, while the inner surface is white.

Diffusion

Mediterranean – Northern Adriatic Sea. Here, the oyster was introduced through human intervention (anthropic input).

Western Atlantic – This species originates from the North American Atlantic coast. Today, it is found from the Gulf of St. Lawrence in Canada to the Gulf of Mexico, the Caribbean, Brazil, and Argentina.

Eastern Atlantic – Introduced for aquaculture purposes, particularly in the United Kingdom.

Pacific Ocean – Present in Hawaii, Japan, Australia; from British Columbia down to the U.S. coast.

Meats

Flavorful and meaty, these are widely appreciated by international chefs.

FLAT OYSTER

Ostrea Edulis

FAO Name

OYF

Length

Maximum 20 cm

Distinctive Characters

These oysters have a characteristic round shape. It has a notable polymorphism that sets it apart from others. Both valves have the same external outline: the upper one is heavily covered with scales and has barely noticeable growth lines, while the lower one is more convex and larger, with frilled edges.

Coloring

The external color varies from gray to brownish to dark green. The inner surface is white.

Diffusion

Mediterranean – it’s the most widespread and therefore the most common oyster in the region.
Eastern Atlantic – found from Morocco to Norway.

Meats

Tasty and firm, typically eaten raw.

Types

Belon

Belon Flat Oyster

AUSTRALIAN CUPPED OYSTER

Saccostrea Cuccullata

Length

Maximum 20 cm

Distinctive Characters

The shell is robust and highly variable in shape. The upper valve is relatively smooth with slight serrations, while the lower valve is convex with strong radial ribs near the edge. Along the inner margin of both valves, a series of crenulations can be seen, forming the ridges on the lower valve.

Coloring

The outer shell color is described as “off-white” with grayish, brown and purplish hues. The inner surface is white and iridescent, displaying a rainbow-like sheen.

Diffusion

Mediterranean – Eastern Basin (Turkey, Egypt). This oyster arrived from the Red Sea, likely entering through the Suez Canal. Due to human introduction, it is also found in the Venetian Lagoon.

Eastern Atlantic – From Cameroon to Angola.

Indo-Pacific – This species originates from the Australian coast. It is also found along the southern and eastern coasts of Africa, the Red Sea, the Persian Gulf, and as far as Eastern Polynesia (Japan, New South Wales and New Zealand).

Meats

Firm and flavorful, they are almost always eaten raw.

Types of Oysters: the main species found in non-european waters

Let’s now take a look at the main oyster species found in non-European waters, specifically the Kumamoto Oyster, the Australian Oyster and the Chilean Oyster.

KUMAMOTO OYSTER

Crassostrea Sikamea

Distinctive Characters

Compared to Crassostrea gigas, Crassostrea sikamea oysters grow more slowly and reach a smaller size. They also have a deeper left valve. Both valves display more pronounced ridges and frilled edges. Initially classified as a subspecies of Crassostrea gigas, sikamea was officially recognized as a separate species in 1975.

Coloring

The outer shell tends to be gray, brownish, or purplish. The interior is, instead, white.

Diffusion

Pacific Ocean – this species originates from Japanese waters. The first farming experiments were conducted in the waters of Kumamoto, which gave the oyster its common name. It wasn’t until the mid-20th century that they were introduced to the U.S., particularly along the northwestern coast, for aquaculture purposes. From there, greater hybridization occurred with Crassostrea gigas.

Meats

Delicate in flavor, best enjoyed raw.

AUSTRALIAN OYSTER

Ostrea Angasi

FAO Name

OGQ

Length

Maximum 25 cm

Distinctive Characters

This oyster species is recognizable by its robust, oval or triangular shape. The upper valve is flat and displays distinct growth rings, while the lower valve is more convex with more or less pronounced radial ribs.

Coloring

The outer shell can be found in these colors: green-purple, brownish-purple, gray, olive-brown. The interior is white and pearlescent, with darker tinges along the edges.

Diffusion

Pacific Ocean – this species is exclusively found in southern Australian waters, including the western and southeastern coasts. It is also present in Tasmania.

Meats

Tasty and firm, typically eaten raw.

CHILEAN OYSTER

Ostrea Chilensis

FAO Name

OCH

Length

Maximum 9 cm

Distinctive Characters

The shell is known for its sturdiness and has an oval to subcircular shape. The upper valve is flat and scaly, while the lower one is convex. Both valves have growth rings, although the lower valve shows more concentrated striations near the edges.