G. Brown (George Brown) Goode.

The fisheries and fishery industries of the United States (Volume 1:1) online

. (page 124 of 146)
Online LibraryG. Brown (George Brown) GoodeThe fisheries and fishery industries of the United States (Volume 1:1) → online text (page 124 of 146)
Font size
QR-code for this ebook


the foregoing description of the digestive apparatus of the animal; and the colorless blood-cells,
moving in a thin, watery liquor sanguinw, would, judging from their amoabifonn character, readily
absorb any tinge acquired by the latter from the intestinal juices.

217. LOCAL VARIATIONS IN THE FORM AND HABITS OF THE OYSTER.

Mr. Darwin ("Variation of Animals and Plants," vol. ii, 2d ed., p. 270) writes: "With
respect to the common Oyster, Mr. F. Buckland informs me that he can generally distinguish the
shells from different districts; young Oysters brought from Wales and laid down in beds where
*nn<j'res' are indigenous, in the short space of two months begin to assume the 'native' character.
M. Costa 1 has recorded a much more remarkable case of the same nature, namely, that young



1 Bull, de la Soc. Imp. d'Accliraat., viii, p. 351.



EFFECT OF HEAT UPON OYSTERS. 7 I.",

>lu-lls taken from tin- shores of England and placed in the Mediterranean at once altered their
manner of growth and formed prominent diverging rays, like those on the shells of the projHsr
Mediterranean Ojster. The same individual shell, showing Itoth forms of growth, wan exhibited
before ii soeiety in Paris."

VARIATIONS IN THE SHELL. The statement by Mr. lluckland in regard to the local forms of
Ontrva tduli is- undoubtedly true, as I know from personal observation of speeiinens obtained for
iin- troin various parts of Europe through the efforts of Professor Baird. In some cases the local
differences between the shells from different places were so marked that had a person mixed certain
lot* together indiscriminately without my knowledge 1 could afterwards certainly have sorted out
the more marked varieties. Local influences also very largely determine the " greening" of Oysters,
as I can assert from personal observation of botli the American and Euro|>ean species. Practical
oNstermen affirm that they can readily discriminate the local varieties of Oysters grown in various
noted localities along the eastern coast of the United States. From what I have seen it is very
probable that this may be the case, as one may often observe well-marked differences of form as
well as color.

Local adaptation undoubtedly takes place, for how else are we to account for the fact that
a change in the specific gravity of the water to which the adult has lieen accustomed will kill the
milt? This point has an important practical bearing in relation to the effect of heavy rains iu
diluting the water when the animals are spawning. Might not a marked change in the si>ecitic
gravity of the water at the time of spawning kill all the spermatozoa which are set free, and thus
also prevent the impregnation of whatever mature ova were being thrown out at that time by
the ad ults f

iNFU'ENCE OF TEMPERATURE. Certain it is that temperature has an influence upon the
time of spawning. A lot of Oysters marked "Anglo-Portuguese," which had been transplanted
from Portuguese to English waters, and which I received in the month of March and others
in January last, had the reproductive organs remarkably advanced in development as compared
with specimens of 0. edulix from different parts of England, Wales, Scotland, Holland, and France.
So great was this difference that, although planted for some time in the colder waters of England,
the reproductive organs of the Portuguese form had not apparently had their disposition to
become functionally active at this early season influenced to any great extent. In fact, I obtained
living mature eggs and milt from a number of specimens of this variety, while I looked in vain
for ripe spawn in any of the others of the true O. edvUtt. This would indicate that the influence of
temperature, though not altogether hereditary in this case, was insistent, and had so impressed
itself that the reproductive organs of these Oysters, coming from a warmer latitude, had begun
to mature their sexual products even after transplanting into more northerly and wilder waters
much sooner than the natives of those same latitudes.

Like this persistent influence of a climate to which certain forms of Oysters have been long
accustomed, the influence of the specific gravity of the water of a certain locality may also be
persistent. The Oysters of Saint Jerome's Creek seem to be adapted to the specific gravity of
the water of the vicinity, so that if artificial sea-water is prepared, differing much in this re-. ml
from the native water, we find that the spermatozoa are immediately killed if put into it. From
this it follows that if the specific gravity to which the adults become accustomed is normal to
their sexual products, may it not be well to look into the effect of such changes upon the health
of the ad ults f

I have met with spawning Oysters in December, such at least in which the spawn was nearly
mature, but this was an exceptional case. I find them in April and May in considerable abun-



744 NATURAL HISTORY OF AQUATIC ANIMALS.

dance; the months of May, June, and July may, however, be regarded as their principal spawning
months. Ripe spawn may be sparingly obtained in the latter part of August, and even np to
the first of October, but the three months mentioned are the periods during which the experi-
mentalist ought to be in the field prepared for work in this, the latitude of Washington. What
amount of variation from this period may be made manifest as we go north or south along the
eastern coast of the United States I am unable to state; and what amount of local variation may
also be due to causes of a purely local character I am also unable to say, not having examined
the Oysters at a sufficient number of localities to make such facts as I may possess of any
value.

218. THE OYSTER-CRAB AS A MESSMATE AND PURVEYOR.

It is many years since Mr. Say named the little Oyster-crab Pinnotheres ostreum, and its habits
since that time seem to have excited but little interest. Professor Verrill, in his observations pub-
lished in the "Report of the United States Fish Commissioner for 1871-'72," records the fact that
it is the female which lives in the Oyster, and that the male, which is smaller and unlike the
female, especially in the form of the abdominal segments of the body, is rarely if ever seen to
occur as a messmate of the Oyster, but that he has seen it swimming at the surface of the water
in the middle of Vineyard Sound. He also says that they occur wherever Oysters are found.
This singular little crab has quite a number of allies which inhabit various living mollusks, holo-
thurians, etc., of which admirable accounts are given by Van Beneden in his work on "Animal
Parasites and Messmates," and also by Semper in his treatise entitled "Animal Life."

QUADRUPLE COMMENSALISM. The Oyster-crab is a true messmate, and it is in the highest
degree probable that the presence of these animals in the mantle cavity of the Oyster is to be
regarded as advantageous rather than otherwise. The animal usually lives between the ventral
lobes of the mantle of its host, into which the four lobes of the gills and palps also depend,
and, as will be seen from the following observations, may be the means of indirectly supplying
its passive protector with a portion of food. During a trip down the Chesapeake in July, 1880,
while I was with the Fish Commission vessel, some Oysters were dredged up by the crew which
contained some Oyster-crabs. In the case I am about to describe the included crab was a female
with the curiously expanded, bowl-like abdomen folded forward under the thorax, partially
covering a huge mass of brownish eggs. Upon examining these eggs, what was my astonish-
ment to find that they afforded attachment to a great number of compound colonies of the
singular bell animalcule, Zoiithamnium arbusculum. Upon further examination it was found that
the legs and back of the animal also afforded points of attachment for similar colonies, and
that here and there, where some of the individuals of a colony of Zoiithamnium had been sepa-
rated from their stalks, numerous rod-like ribriones had affixed themselves by one end. In this
way it happens that there is a quadruple commensalisin established, since we have the vibriones
fixed and probably nourished from the stalks of the bell animalcule, while the latter is benefited
by the stream of water drawn in by the cilia of the Oyster, and the last feeds itself and its protege,
the crab, from the same food-laden current. Possibly the crab inside the shell of its host catches
and swallows food which in its entire state could not be taken by the Oyster, but in any event
the small crumbs which would fall from the mouth and claws of the crab would be carried to
the mouth of the Oyster, so that nothing would be wasted.

We must consider the crab with its forest of bell animalcules in still another light. Since
the animalcules are well fed in their strange position, it is but natural to suppose that they would



DEVELOPMENT OF THE OYSTER-CRAB. 745

propagate r:ij)i(lly, and that tin- branches of the curious tree-like colonies would also increase in
numbers. The individuals of the colonies multiply in at>out three ways: drat, by liranrliin^ ;
secondly, by splitting lengthwise; thirdly, certain much enlarged and overfed /of.ids divide cn.ss
wise. My the two last modes one-half of the product is often set free, the free animalcules
s<> originated being known as "swarmers." These cast-oft' or free zooids which drop from the
colonies are no doubt carried along by the vortex created by the cilia of the gill and palps, and
hurled into the mouth and swallowed as part of the daily allowance of the food of the Oyster.
\Ve may therefore regard I'innothrrrM, in such instances, as a veritable nursery, upon the body and
legs of which animalcules are continually propagated and set free as part of the food supply of
the Oyster, acting as host to the crab. I do not suppose, however, that such a condition will
always be found to obtain, and it must also be remembered that myriads of Zoiithnniniiim colonies
were dredged up attached to the fronds of the handsome (trinneliu, a red alga commonly found
in certain parts of Chesapeake Hay. Where this plant grows in abundance on the bottom I have
estimated that one might find upwards of a hundred animalcules attached to a square inch of
frond surface, which would indicate an animalcular population of upwards of four millions of
individuals to the square rod, a number as great as that of the human inhabitants of the city of
London.

DEVELOPMENT OF THE OYSTER CRAB. The Oyster-crab undergoes a development and
metamorphosis similar to that of our edible crab, Callinectes, but the body in the Zotea stage
is blotched with dark, branched pigment cells. The eyes also are vastly more developed than
in the adult, where they are partly suppressed from disuse. There is no dorsal spine, nor are
the antcnuary and rostral appendages so well developed as in the Zowa of Callinecte*. After the
young are hatched they probably leave the abdominal covering of the parent, swim out of the
Oyster for a season, and, if female, seek a permanent abode in some Oyster near by, behaving
somewhat like the species described by Semper as inhabiting the water-lungs of certain holothu-
rians. After undergoing further development, the young Pinnotheres reaches the megalops stage
of its development, when it is probable that the choice of its home takes place. After it has
entered the mantle cavity of its host as a diminutive larva, and has grown to be adult, when
it measures a half inch or more in diameter, it is probably ever after a prisoner within the
shell of its mollusc-mi protector. It undergoes a retrogressive metamorphosis as it grows adult,
its eyes become relatively less conspicuous than in youth, and it never has a thick, hard shell
like its allies which live in the open water, but the external skeleton remains almost entirely sott
and chitinous, or in the state in which we commonly find the outer covering of an edible crab
which h;is just molted. This arises apparently from the conditions by which the animal is sur-
rounded; the protection afforded it by its host does away with the need of a thick, hard covering
such as we find inclosing the bodies of its free-swimming allies. Unlike the latter, too, the limbs
of the Oyster-crab are to some extent degenerate and weakened; its chelre or claws are feeble,
and, when removed from its home, seems a very sluggish, helpless sort of creature, without a
particle of the pugnacity of its allies, and if placed on its back will sometimes remain in that
position helplessly heating the air with its weak limbs. This is a remarkable instance, which also
sei\es very admirably to illustrate the principle of degeneration in organic evolution, so ably
dealt with by Prof. E. Ray Laukester.

The Oyster itself is also an example of the effect of disuse in producing retrograde develop-
ment, and even shows signs of gradual adaptation when removed from one locality i> another.
Unlike most other bivalves, the Oyster has no soft muscular foot which it may protrude outward
from between the edges of its valves. No visible rudiment of such a prominence can be found



746 NATURAL HISTORY OF AQUATIC ANIMALS.

iu the adult, though something of the sort, it is asserted by embryologists, appears to be devel-
oped in the larvas. As the Oyster lost its power of locomotion IVom the noa-development of
the foot, due doubtless to a gradually acquired sedentary habit which has become permanent.
the pedal structures have been almost entirely aborted, leaving nothing excepting the poorly
developed pedal muscles described by Dall. There is accordingly little or no evidence of the
existence of a pedal or foot ganglion in the Oyster, because there is no need for one, as in other
forms; it, too, has disappeared with the structure which required its presence.

Returning to the consideration of the Oyster-crab, it is well known that.it is much relished
by many persons. The animal may be eaten alive, and has a peculiar, agreeable sweetish taste.
Recently an enterprising New York party has taken to canning them, the supplies for this purpose
being obtained from some of the large oyster-canning establishments. The ecor.omic value of the
animal as food, although not great, is sufficiently important to demand a passing notice.

219. PHYSICAL AND VITAL AGENCIES DESTEUCTIVE TO OYSTERS.

Most of the observations which follow were made at Saint Jerome's Creek, Maryland, but
inasmuch as the physical and vital enemies of Oysters appear to be similar the world over, I have
no hesitation in reproducing what I have previously published elsewhere. And of physically
injurious agents the black ooze or mud found in the vicinity or on the bottom of many of our
most valuable beds and planting grounds is probably the most to be dreaded if it accumulates
in too great quantity.

The origin of the black ooze at the bottom can be traced directly to the sediment held iu
(suspension in the water which slowly ebbs and flows in and out of the inclosure, carrying with it
in its going and coming a great deal of light organic and inorganic debris, the former part of which
is mainly derived from the comminuted fragments of plants growing in the creek. This seemed to
be the true history indicated by what was noticed in studying the box-collector. The same opinion
is held as to the origin of this mud by both Coste and Fraiche in their works on oyster-culture.

There is probably no worse enemy of the oyster-culturist than this very mud or sediment.
It accumulates on the bottom of the oyster-grounds, where iu course of time it may become dee])
enough to cause, serious trouble. Especially is this true of ponds from which the sea ebbs, and to
which it flows through a narrow channel. The Jailing leaves from neighboring trees in autumn
also contribute to this pollution, as well as heavy rains which wash deleterious materials into it.

Adult Oysters which are immersed in part in this mud struggle hard to shut it out from
their shells. If one will notice the inside of the shells of Oysters which have grown in a muddy
bottom, it will often be seen that there are blister-like cavities around the edges of the valves
filled with mud, or a black material of a similar character. There is not the slightest doubt
in my mind that in these cases the animal, in order to keep out the intruding mud, has had
recourse to the only available means at its command. A great many of the Oysters in the pond
are affected in this manner, but it is extremely uncommon to find shells of this kind in opening
Oysters coining from a hard bottom. It is easy to understand that such efforts at keeping out
the mud from the shell will not only waste the life forces of the animal, but also tend to greatly
interfere with its growth. The importance, therefore, of artificial preparation is apparent, where
it is desirable to establish ponds for the successful culture of this mollusk.

Only in one case have I observed that the mud tended to impair the flavor and color of
the Oyster. In this instance the animal was thoroughly saturated with the black ooze, the very
tissues seeming to be impregnated with the color, the stomach and intestine loaded to engorge-
ment with the mud, the animal manifesting every sign of being in a decidedly sickened condition.



EFFECT OF SEDIMENT UPON YOUNU OYSTERS. 747

Tin- cause of this was probably that the shell with its tenant had sunken too deeply Into the
mud when tin- ingest ion of the black ooze commenced, giving rise to the remarkable change*
which 1 lia\e leconled. No doubt had this condition of things jK'rsisted for long the- animal
would ha\e been smothered by the mud.

Mtru AND THE YOUNG FRY. The accumulation of the slightest quantity of sediment around
a young Oyster would tend to impede its respiration, mid in that way destroy it, yet in the natural
beds there are so few naturally clean places which remain so that it is really surprising that so
many young Oysters pass safely through the critical periods of their lives without succumbing to
tln> smothering effects of mud and sediment. When it is borne in mind that at the time the infant
Oyster settles down and lixes itself once and for all time to one place, from which it has no power
to move itself, it measures at the utmost one-eightieth of an inch, it will not be hard to under-
stand how easily the little creature can be smothered even by a very small pinch of dirt. The
animal, small as it is. must already begin to breathe just in the same way as its patents diil before
it. Like them its gills soon grow as little filaments covered with cilia, which cause a tiny current
of water to pass in and out of the shell. The reader's imagination may In- here allowed to esti-
mate the feeble strength of that little current, which is of such vital im|M>rtance to the tiny Oyster,
ami the ease with which it may be stopped by a very slight accumulation of dirt. Mobiiis esti-
mates that each Oyster which is born has 1 14 ^ooo ' a chance to survive and reach adult age. So
numerous and effective are the adverse conditions which surround the millions of eggs matured by
a single female that only the most trifling fraction ever develop, as illustrated by the above calcu-
lation. The egg of the Oyster, being exceedingly small and heavier than water, immediately falls
to the bottom on being set free by the parent. Should the bottom be oozy or comiosed of
sediment its chalices of development are meager indeed. Irrecoverably buried, the eggs do not
in all probability have the chance to begin to develop at all. The chances of impregnation ure
also reduced, because the male and female Oysters empty their generative products directly into
the surrounding water, whereby the likelihood of the eggs meeting with the male cells becomes
diminished. What with falling into the mud and what with a lessened chance of becoming
impregnated, it is not unlikely that Mobius' estimate is very nearly correct ; but the American
Oyster, whose yield of eggs is much greater, not only on account of its larger size, but also
because the eggs are smaller than those of the Knro|>eaii, has probably still fewer chances of
survival. The vigorous growth of small organisms on surfaces fitted for the attachment of young
Oysters also tends to cause sediment to gather in such places in the interstices of the little
organic forest, where the eggs of the Oyster no doubt often become entombed or smothered by the
crowded growth surrounding them.

" In addition to the active, animate enemies of the Oyster, the beds suffer seriously, at certain
times, from the elements. . . . Great storms will sweep the Oysters all off the beds, bury
them under shifting sand or mud, or heap upon them the drifting wrack torn from the shores.
Beds which lie at the mouths of rivers are liable to be injured by floods also, which keep the
water wholly fresh, or bring down enormous quantities of silt and floating matter, which settle*
on the beds and smothers the Oysters. .

" A few years ago a large tract of peat was drained at Grangemoutb, Scotland. The loose
mud and moss was carried down the drains tqiou an oyster-bed in the estuary; the consequence
was that the Oysters were covered over with mud and entirely destroyed. Nothing is so fatal to
Oysters as a mud storm, except it be a sand storm. The mud and the sand accumulate in the
Oyster's delicate breathing organs and suffocate him.

North of Long Island an enemy is found which does not exist in the milder south, in the



748 NATURAL HISTORY OF AQUATIC ANIMALS.

shape of 'ground-ice' or 'anchor-frost.' It is little understood, though often experienced, and I
was able to collect only vague data in regard to it. It appears that in hard winters the bottom of
the bays freezes solid in great patches, even at a depth of fifteen or twenty feet. The mud freezes
so hard that rakes cannot be pressed into it; and if a stronger implement, like a ship's anchor, is
able to penetrate it. the crust comes up in great chunks. These frozen patches are sometimes
forty feet square and continue unthawed for long periods. When such 'anchor-frost' takes place
at an Oyster-bed, of course the mollusks are frozen solidly into the mass, and few of them ever
survive the treatment. To the Cape Cod planters this is a serious obstacle to success." 1

INTERFERENCE OF OTHER ANIMAL LIFE. We have called attention to the probable inter-
ference of small organic growths to the fixation of the young fry; in practice it is found that the
larger organic growths which establish themselves on the collectors also become injurious. The
two most conspicuous types are the sessile ascidians or tunicates and the barnacles. 1 have
frequently found Inlly one-half of the surface of a slate covered with a dense colony of ascidians;
in this condition a great percentage of available surface is lost which ougUt to serve for the
attachment of spat. The surfaces so occupied would also be comparatively clean were it not for
these organisms, which actually become a serious annoyance. They, like the Oyster, affix
themselves to the slates while still in the free-swimming larval stage, since the surfaces designed
for the Oyster are equally well adapted to them. The barnacles, which also affix themselves in
great numbers, become a nuisance for the same reason. The larval barnacle is an extremely
active little creature, and dashes about in the water with great rapidity. As soon as it has
completed this stage of its growth it betakes itself to some object, to the surface of which it
attaches itself by the head end, when a singular change takes place, at the end of which it is
found that it has begun the construction of the curious conical shell which it inhabits. They
grow very rapidly, so that in a couple of months the shell will already measure over half an inch
in diameter. In this way further inroads are made upon the room which should be taken up by
Oysters.

Of course the larger types are not alone in taking up space, since infusorians, bryozoans,
polyps, etc., are also culpable, as well as algae, such as diatoms and the higher torms. The only
remedy for this accumulation of animal growths on the surfaces of the shites and other collecting
apparatus will be to have the frames which hold the slate in position so arranged that each tile,
shingle, or slate can be removed, in order that It may be readily overhauled and these organisms
removed from the surfaces which it is desired shall remain clean. This work would have to be
done at intervals of every two or three weeks, and (hould be conducted with great caie, so as uot



Online LibraryG. Brown (George Brown) GoodeThe fisheries and fishery industries of the United States (Volume 1:1) → online text (page 124 of 146)