The New International Encyclopædia/Oyster
OYSTER (OF. oistre, ouistre, huistre, Fr. huitre, from Lat. ostrea, ostreum, from Gk. ὄστρέον, oyster; connected with ὄστέον osteon, Lat. os, bone). A sessile bivalve mollusk of the family Ostreidæ, especially any of the numerous species, extinct and extant, of the genus Ostrea. The shells are irregular and unequal; the fixed left valve generally spacious, strongly convex without and excavated within; right valve generally plane or concave externally, always less convex than its fellow: both shells beaked; ligamental area elongate or triangular; hinge toothless; adductor impression single and shell subnacreous.
|ANATOMY OF OSTREA VIRGINICA.|
h, Hinge; l, ligament; d, pg, and s
The oyster of the eastern coast of the United States is Ostrea Virginica, a valuable species of protean characters, formerly much subdivided by systematists and almost impossible to diagnose. The shells are lateral and hinged anteriorly, an elastic pad (ligament) causing them normally to gap. Closely applied to their inner faces and extensible beyond their margins are two thin folds (mantle) of the body-wall, which secrete the shell in successive layers within and on the margins. The mantle encloses a chamber (mantle cavity) open ventrally and posteriorly, into which project on each side a pair of gills, commonly called the ‘beard,’ and in front of these a pair of smaller fleshy lobes (palps). Above the gills and palps lies the body, containing the digestive, reproductive, circulatory, excretory, and nervous systems, and the adductor muscle which closes the shells. The adductor (popularly, the ‘eye’ or ‘heart’) lies somewhat behind the middle of the body, the dark scars on the inside of empty shells marking its attachments. The funnel-shaped mouth lies between the two pairs of palps. A short gullet leads into a spacious stomach, and this into the tubular intestine which opens by an anus above the adductor. Surrounding the stomach is the liver, a large dark green digestive gland opening into the stomach by numerous ducts. In front of the adductor lies the pericardium, containing the two-chambered heart and in proximity to the excretory organ. The simple degenerate nervous system consists of two pairs of ganglia, one above the gullet and the other beneath the adductor, connected by a pair of nerve cords.
The sexes are separate, but without external distinction. The sexual glands when ripe are creamy white organs surrounding the digestive system and opening on each side beneath the adductor. In Long Island Sound spawning occurs from May to August, in Chesapeake Bay from April to October, in South Carolina as early as March, and in Florida as early as February. In oysters transplanted during the spawning season reproduction is often interfered with or arrested. An average oyster will produce 16,000,000 eggs and a very large one 60,000,000. When ripe the sexual products ooze from the genital openings and fertilization results from their accidental meeting in the water. Segmentation results in five or six hours in the production of a ciliated gastrula, a cup-shaped, free-swimming organism, often carried by the currents to found new and remote beds. An embryonic shell soon appears, and the little oyster sinks to the bottom, where, if favorably situated, it becomes attached by its left valve and gradually assumes the adult form. The recently attached spat is 1.80 to 1.90 of an inch in diameter, and its subsequent growth varies with its environment. Single oysters on firm bottom become round and deep, but those in clusters or on soft bottom grow irregular and elongate. On undisturbed natural beds they grow in clusters, and the beds repose, as a rule, on a muddy substratum upon which they have been built up from a comparatively small nucleus by the fixation, year after year, of the young upon the shells of their predecessors.
Oysters live from above low-water mark to a depth of 1.5 fathoms, where the density is between 1.002 and 1.025, the optimum being from 1.011 to 1.022, and in a range of temperature which in Chesapeake Bay extends from 32° F. to 90° F. The embryos and fry require more equable and stable conditions, the temperature required being between 68° F. and 80° F. The best and most productive beds are commonly in strong tidal currents, which desseminate the fry and food and keep the old shells clean enough to catch the spat. Diatoms constitute about 90 per cent. of the oyster's food, the rest consisting of other small plants and animals, and in the breeding season of its own eggs and fry. The latter are eaten by other mollusca also, and from its attachment until it reaches a large size the oyster is preyed upon by starfish, drills (Urosalpinx), drumfish, rays, and other aggressive enemies, while it wages a passive fight against starvation and suffocation with mussels, barnacles, sponges, worms, aquatic vegetation, and other prolific- or luxuriant organisms growing on the beds.
Ostrea Virginica occurs from the Gulf of Saint Lawrence to the tropics, but between Cape Breton and Cape Cod the Sheepscot River, Maine, is its only locality. It has also been introduced in San Francisco Bay, where it breeds to a limited extent. The yield of Eastern oysters at the beginning of the present century was as follows:
|South Atlantic States||1,612,181||384,934|
|Middle Atlantic States||19,749,677||10,286,556|
|New England States||2,649,072||1,910,684|
The greatest production is in Chesapeake Bay, where the principal yield is from the natural beds. Most of the oysters from New England and from New York and the outer coast of New Jersey are produced by planted beds; the entire yield of the Pacific Coast is similarly derived, and there has been recently a considerable increase in oyster culture in New Jersey, Virginia, and other States. The number of persons engaged in the industry is estimated at upward of 60,000, but as many of them are employed part of the year in other fisheries, farming, etc., definite statistics are not available. Baltimore is the most extensive market and New York has a considerable export trade with Europe.
The native oyster of the Pacific Coast is Ostrea lurida, a small thin-shelled species. It is hermaphroditic, and, like the European oyster, retains its young for a time in the mantle cavity. In 1901 159,340 bushels, valued at $251,192, were marketed, principally on the Pacific Coast.
PACIFIC COAST OYSTER.
The European oyster (Ostrea edulis) is found from Italy to Norway. It is a round thin-shelled species, more shapely than the American species, and hermaphroditic, first female and afterwards male. It is less prolific than its American relative and the young undergo considerable development in the mantle chamber of the mother. It thrives in water of full, or almost full, organic density. The Portuguese oyster (Ostrea angulata) sexually and in its habits more closely resembles Ostrea Virginica.
The oysters of Japan are Ostrea cucullata, which occurs in shallow and moderately brackish or moderately salt water throughout the whole archipelago; and Ostrea gigas, a very large salt water species found in deep water. Many other species of Ostrea are found in temperate and tropical seas throughout the world.
Fossil Oysters. The oyster family appears to have had its origin in some imperfectly known forms, such as Ostrea nobilissima of the Carboniferous. The family is found also in the Permian. In the Triassic it is represented by a strongly plicated form, Alectryonia, which form becomes more prominent in the Jurassic and Cretaceous. There are also the common arcuate shells of Gryphæa and Exogyra in the Jurassic and Cretaceous. Ostrea itself is known in the Mesozoic, but it attained its maximum of size and abundance in the Tertiary. The sandy marls of this period in the Southeastern United States often contain great numbers of very large specimens of oysters, especially of two species, Ostrea Georgiana and Ostrea sellæformis. Consult White, C. A., “A Review of the Fossil Ostreidæ of North America and a Comparison of the Fossil with the Living Forms,” Annual Report of the United States Geological Survey, vol. iv. (Washington, 1883).
Oyster Culture. Owing to the exhaustion of the natural beds and their inability to supply the demand for oysters, it has been found necessary to resort to artificial methods of production, effecting (1) an increase in the number of eggs fertilized; (2) an increase in the surfaces available for fixation, and also of the number of spat attaching; (3) the saving of spat and young oysters which would naturally fall victims to enemies and adverse physical conditions; and (4) the utilization of barren bottoms and naturally unavailable food supplies. But a small part of the area under water suitable for oysters has been utilized by nature, mainly for lack of suitable bodies for the attachment of the young. In the United States such barren bottom is utilized by clearing it of all rubbish and either planting ‘cultch’ to collect the spat, or else young oysters (seed), that they may improve in size, shape, and quality under conditions safer and more favorable than in their original environment. In certain places either method may succeed, but commonly a locality is better adapted to one than the other.
The most suitable bottom for oyster culture consists of firm mud or of a firm substratum with a thin surface of soft mud, but stable sandy bottom is often used with success. Rocky bottom is usually deficient in food, loose sand drifts and covers the oysters, and very soft mud ingulfs and stifles them or produces inferior elongate stock. Mud naturally too soft may be utilized by distributing over it shells, sand, or other material, which, resting on or near the surface, furnishes a firm foundation upon which the growing oyster may repose in security. For spat-collecting it is frequently advantageous to use hard mud, gravel, or rocky bottom in shoal water, ill adapted to adult oysters from deficiency of food. The bottom being properly prepared and its boundaries marked with stakes or buoys, either system may be adopted to accord with circumstances. Generally seed-planting is more certain in its results and yields quicker returns to the grower. Seed-oysters vary from ‘blisters’ ½ inch in diameter to individuals almost ready for market, but ordinarily they are between 1 and 3 inches long. They are obtained from planters making a specialty of seed production or from natural beds, their cost varying from 10 cents to $1 per bushel, the larger culled stock, separate, well shaped, and free from rubbish, bringing higher prices and giving the best results. From 300 to 600 bushels of culled seed per acre are used, a larger quantity of ‘rough’ material being required, as much of it consists of old shells and debris. It is usually sowed broadcast with shovels from boats. Further attention, other than that required to keep the beds clean and free from enemies, is generally unnecessary, especially if culled seed has been used.
The system of spat-collecting is often extremely productive, though sometimes, for reasons not well understood, it results in complete failure. Spat will attach to almost any clean solid body, but certain materials, from their shape, structure, or cheapness, possess advantages which commend them. The most widely used and one of the best forms of cultch consists of the clean shells of the oyster itself. They are cheap, readily obtainable in all oyster regions, and, owing to their size and shape, can be used with success on bottom too soft for most other materials. The principal objection to them is that so many spat sometimes attach to a shell that they have no room for growth, and scallop (Pecten), jingle (Anomia), and other small fragile shells are sometimes preferable, as they catch the spat in smaller clusters and tend to break up as the oysters grow, but, owing to their lightness, they cannot be used in strong currents. The cost of oyster shells is from 2 to 5 cents per bushel, and sometimes they may be had for the hauling. Coarse gravel, pebbles, and crushed stone are used to a considerable extent in Long Island Sound and vicinity, but require a harder bottom than shells. The particles average about the size of a walnut or smaller, and as but few spat attach to each, the oysters are well shaped, less laborious to cull, and a larger proportion survive. This material costs from 5 to 8 cents per bushel and the cost of planting is about the same as of shells, ½ to 5 cents per bushel, according to local conditions.
Shells, stones, and gravel are distributed, like seed, from boats or scows. From 250 to 600 bushels per acre are used, soft bottom requiring more than hard. If there are extensive beds of adult oysters in the vicinity, and especially if the currents set from them to the spat-beds, they can be depended upon to supply the fry, but if not, adult oysters should be used in the proportion of 30 to 60 bushels per acre. The brood oysters should be planted several months before the spawning season, but the cultch should not be put down until spawning is about to begin, that it may be free from slime and sediment when the fry is ready to fix, even a thin coating of sediment being sufficient to suffocate the young oyster at that period.
Some planters allow the beds to remain unworked until the crop is ready to market, but to produce oysters of superior shape and quality, the clusters should be taken up and separated as soon as they can be culled without injury. It frequently happens that good localities for obtaining a set are not favorable to the production of marketable oysters, and in this case the culled young may be transplanted with advantage and profit to beds possessed of an environment more favorable for the adults. Whether cultch or seed be planted, the beds should be closely watched to protect them from enemies which sometimes work havoc unsuspected until the time comes to market the crop.
The United States Fish Commission is experimenting with a system of fattening oysters artificially, by using fertilizers to stimulate the production of oyster food in ponds. Good results have been attained, but the commercial feasibility of the method has not yet been demonstrated. The alleged method of fattening oysters by feeding with corn meal is worthless. ‘Plumping’ them by placing in fresh or nearly fresh water is a bloating and not a fattening treatment, and is less resorted to than formerly. Oysters should not be planted or bedded in the vicinity of sewage contamination, as they may thereby become sources of disease infection, but there is no danger to be anticipated from the consumption of oysters from beds remote from sources of contamination. Green oysters are sometimes placed on the market. There are three types of greenness, two of which are perfectly harmless. The third type is evidently a pathogenic condition, correlated with the presence of copper; but, while the affected oysters are poor in quality, it is not demonstrated that they are dangerous.
1, Unfertilized egg shortly after mixture of spawn and milt; spermatozoa are adhering to the surface. 2, Same egg a few minutes after fertilization; polar body at broad end. 3, Optical section of egg 27 hours after impregnation, showing two large cells, covered by a layer of small ectodermal cells. 4, Optical section of an older egg, now become flattened from above downward. 5, An embryo with well-developed larval shells.
In England oyster culture is practically along the same lines as in the United States. Shells are used to collect the spat, and seed-oysters are planted in favorable places, notably on the bottoms controlled by the Whitstable Company, a coöperative corporation. On the Continent the methods are more elaborate, the low price of labor and the high price of oysters, as well as the restriction of the area upon which they can be grown, tending to encourage an intensive system of culture. Tiles and fascines are generally used as spat-collectors, and especially in Holland and France a system of ponds or ‘claires’ is used for growing and fattening. Japanese methods somewhat resemble those of France and Holland in the recognition of a distinction between the bottoms used for spat-collection and for growing, although ponds are not used. Bamboo branches in regular arrangement are used for spat-collectors and the oysters are usually twice transplanted, first to a place favorable for rapid growth, and finally to beds especially rich in food, where they fatten.
Bibliography. Huxley, Oysters and the Oyster Question (London, 1883); Ingersoll, The Oyster Industry (Washington, 1887); Brooks, The Oyster (Baltimore, 1891); Dean, Report on the European Methods of Oyster Culture (Washington, 1893); Moore, Oysters and Methods of Oyster Culture (Washington, 1897); Herdmann and Boyce, Oysters and Disease (London, 1899); Pottier, Les huitres comestibles et l'ostréiculture (Paris, 1902). Also the reports of the several State oyster commissions, and especially the United States Fish Commission Reports and Bulletins.
- Value to oystermen and growers.