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thence to the left side of the vent, and there ends by an opening of
its own.

Now, the air-bladder of all fishes is, to begin with, an outgrowth
from the front part of the alimentary canal, and there are a great
many fishes in which, as in the herring, it remains throughout life in
permanent communication with the gullet. But it is rare to find the
duct so far back as in the herring ; and, at present, I am not aware
that the air-bladder opens externally in any fishes except the herring
and a few of its allies.

There is a general agreement among fishermen that herrings some-
times make a squeaking noise when they are first taken out of the
water. I have never heard this sound myself, but there is so much
concurrent testimony to the fact that I do not doubt it ; and it occurs
to me that it may be produced, when the herrings are quickly brought



THE HERRING. 437

up from some depth, by means of this arrangement. For under these
circumstances the air which the air-bladder contains expands to such a
degree, on being relieved from the pressure of the water, that deep-sea
fishes with a closed air-bladder which are brought to the surface rap-
idly are sometimes fairly turned inside out by the immense distention,
or even bursting, of the air-bladder. If the same thing should hap-
pen to the herring, the like misfortune would not befall it, for the air
would be forced out of the opening in question, and might readily
enough produce the squeak which is reported. The common loach* is
said to produce a piping sound by expelling the air which this fish
takes into its intestine for respiratory purposes.

At the opposite end of the air-bladder there is an even more curious
arrangement. The silvery coat of the air-bladder ends in front just
behind the head. But the air-bladder itself does not terminate here.
Two very fine canals, each of which is not more than a two-hundredth
of an inch in diameter, though it is surrounded by a relatively thick
wall of cartilage, pass forward, one on each side, from the air-bladder
to the back of the skull. The canals enter the walls of the skull, and
then each divides into two branches. Finally, each of these two
dilates into a bag which lies in a spheroidal chamber of corresponding
size and form ; and, in consequence of the air which they contain,
these bags may be seen readily enough shining through the side-walls
of the skull, the bone of which has a peculiar structure where it sur-
rounds them. Now, these two bags, which constitute tjie termination
of the air-bladder on each side, are in close relation with the organ of
hearing. Indeed, a process of that organ projects into the front cham-
ber on each side, and is separated by only a very delicate partition
from the terminal sac of the air-bladder. Any vibrations of the air
in these sacs, or any change in the pressure of the air in them, must
thus tell upon the hearing apparatus.

There is no doubt about the existence of these structures, which,
together with the posterior opening of the air-bladder, were most accu-
rately described, more than sixty years ago, by the eminent anatomist
"Weber ; but I am afraid we are not much wiser regarding their mean-
ing than we were when they were first made known. In fishes in gen-
eral, there can be little doubt that the chief use of the air-bladder is to
diminish the specific gravity of the fish, and, by rendering its body of
nearly the same weight as so much water, to render the business of
swimming easier. In those fishes in which the passage of communi-
cation between the air-bladder and the alimentary canal is closed, the
air is no doubt secreted into the air-bladder by its vessels, which are
often very abundant. In the herring the vessels of the air-bladder are
very scanty ; and it seems probable that the air is swallowed and
forced into the air-bladder just as the loach swallows air and drives it

* See Miillcr, " Ueber Fische welche Tijne von sich geben (" Archiv fur Physiologic,"
1S57, p. 267). The herring is not mentioned in lliillcr's list of vocal fishes.



438 THE POPULAR SCIENCE MONTHLY.

into its intestine. And, as I have already suggested, it may be that
the narrow posterior canal which leads from the air-bladder to the
exterior is a sort of safety-valve allowing the air to escape, when the
fish, rapidly ascending or descending, alters the pressure of the water
upon the contained air.

This hypothesis may be put forward with some show of probability,
but I really find it ditficult to suggest anything with respect to the
physiological meaning of the connection between the air-bladder and
the ear. Nevertheless such an elaborate apparatus must have some
physiological importance ; and this conclusion is strengthened by the
well-known fact that there are a great many fishes in which the air-
bladder and the ear become connected in one way or another. In the
carp tribe, for example, the front end of the air-bladder is connected
by a series of little bones with the organ of hearing, which is, as it
were, prolonged backward to meet these bones in the hinder end of
the skull. But here the air-bladder, which is very large, may act as a
resonator ; while in the Jierring the extreme narrowness of the passages
which connect the air-bladder with the ear renders it difficult to sup-
pose that the organ can have any such function.

In addition to the singular connection of the ear with the exterior
by the roundabout way of the air-bladder, there are membranous spaces
in the walls of the skull by which vibrations can more directly reach
the herring's ear. And there is no doubt that the fish is very sensitive
to such vibratipns. In a dark night, when the water is phosphorescent
or, as the fishermen say, there is plenty of " merefire," it is a curious
spectacle to watch the effect of sharply tapping the side of the boat
as it passes over a shoal. The herrings scatter in all directions, leav-
ing streaks of light behind them, like shooting-stars.

The herring, like other fishes, breathes by means of its gills — the
essential part of which consists of the delicate, highly vascular fila-
ments which are set in a double row on the outer faces of each of
the gill-arches. The venous blood, which returns from all parts of
the body to be collected in the heart, is pumped thence into the gills,
and there exchanges its excess of ^carbonic-acid gas for the gaseous
oxygen which is dissolved in sea-water. The freedom of passage
of the water and the great size and delicacy of the gills facilitate
respiration when the fish is in its native element ; but the same pecu-
liarities permitting of the rapid drying and coherence .of the gills, and
thus bringing on speedy suffocation, render its tenure of life, after
removal from the water, as short as that of any fish. It may be
observed, in passing, that the wide clefts behind the gill-covers of the
herring have some practical importance, as the fish, thrusting its head
through the meshes of the drift-net, is caught behind them, and can
not extricate itself. In the herring, the upper end of the last gill-cleft
is not developed into a sac or pouch, such as we shall find in some of
its near neighbors.



THE HERRING. 439

The only other organs of the herring, which need be mentioned at
present, are the milt and roe, found in the male and female herring
respectively.

These are elongated organs attached beneath the air-bladder, which
lie, one on each side of the abdominal cavity, and open behind the
vent by an apertm-e common to the two. The spermatic fluid of the
male is developed in the milt and the eggs of the female in the roe.
These eggs, when fully formed, measure from one sixteenth to one
twenty-fifth of an inch in diameter ; and as, in the ripe female, the
two roes or ovaries stretch from one end of the abdominal cavity to
the other, occupying all the space left by the other organs, and dis-
tending the cavity, the number of eggs which they contain must be
very great. Probably 10,000 is an under-estimate of the number of
ripe eggs shed in spawning by a moderate-sized female herring. But
I think it is safer than the 30,000 of some estimates, which appear
to me to be made in forgetfulness of the very simple anatomical con-
siderations that the roe consists of an extensive vascular framework
as well as of eggs ; and, moreover, that a vast number of the eggs
which it contains remain immature, and are not shed at the time of
spawning.

In this brief account of the structure of the herring I have touched
only on those points which are peculiarly interesting, or which bear
upon what I shall have to say by-and-by. An exhaustive study of the
fish from this point of view alone would require a whole course of
lectures to itself.

The herring is a member of a very large group of fishes spread
over all parts of the world, and termed that of the Clujyeidce, after
Clupea, the generic name of the herring itself. Our herring, the
Clupeu harengxis, inhabits the White Sea, and perhaps some parts of
the Arctic Ocean, the temperate and colder parts of the Atlantic, the
North Sea, and the Baltic, and there is a very similar, if not identical,
species in the North Pacific. But it is not known to occur in the seas
of Southern Europe, nor in any part of the intertropical ocean, nor in
the southern hemisphere.

There are four British fishes which so closely resemble herrings,
externally and internally, that, though practical men may not be in
any danger of confounding them, scientific zoologists have not always
succeeded in defining their differences. These are the Sprat, the Allice
and Twaite Shads, and the Pilchard.

The sprat comes nearest ; indeed, young herrings and sprats have
often been confounded together, and doubts have been thrown on the
specific distinctness of the two. Yet if a sprat and a young herring
of the same size are placed side by side, even their external differences
leave no doubt of their distinctness. The sprat's lower jaw is shorter ;
the shields in the middle of the belly have a sharper keel, whence the
ventral edge is more like a saw ; and tlie ventral fin lies vertically



440 THE POPULAR SCIENCE MONTHLY.

under the front edge of the dorsal fin, or even in front of it ; while in
the herring, though the position of the ventral fin varies a little, it lies
more or less behind the front margin of the dorsal fin. The anal fin
is of the same length as the dorsal, in the herring, longer than the
dorsal in the sprat. But the best marks of distinction are the absence
of vomerine teeth in the sprat, and the smaller number of pyloric
c£Eca, which do not exceed nine, their openings being disposed in a
single longitudinal series.

Shads and pilchards have a common character by which they are
very easily distinguished from both sprat and herring. There is an
horizontal fold of scaly skin on each side of the tail above and below
the middle line." Moreover, they have no teeth in the inside of the
mouth, and their pyloric caeca are very numerous — a hundred or more
— their openings being disposed five or six in a row.

The shads have a deep narrow notch in the middle line of the up-
per jaw, which is absent in the pilchard. The intestine of the shad is
short and straight, like that of the herring ; while that of the pilchard
is long, and folded several times upon itself.

Both of these fishes, again, possess a very curious structure, termed
an accessory branchial organ, which is found more highly developed
in other fishes of the herring family, and attains its greatest develop-
ment in a fresh-water fish, the Jleterotis, which inhabits the Nile. This
organ is very rudimentary in the shad (in which it was discovered by
Gegenbaur *), but it is much larger in the pilchard, in which, so far as
I know, it has not heretofore been noticed. In Chanos and several
other Clupeoid fishes it becomes coiled upon itself, and in Jleterotis the
coiled organ makes many turns. The organ is commonly supposed to
be respiratory in function ; but this is very doubtful.

Herrings which have attained maturity, and are distended by the
greatly enlarged milt or roe, are ready to shed the contents of these
organs, or, as it is said, to spawn. In 1862 we found a great diversity
of opinion prevailed as to the time at which this operation takes place,
and we took a great deal of trouble to settle the question, with the
result which is thus stated in our report :

" We have obtained a very large body of valuable evidence on this
subject, derived partly from the examination of fishermen and of others
conversant M'ith the herring-fishery ; partly from the inspection of the
accurate records kept by the fishery oflicers at different stations, and
partly from other sources ; and our clear conclusion from all this evi-
dence is, that the herring spawns at two seasons of the year, in the
spring and in the autumn. "VVe have hitherto met with no case of full
or spawning herrings being found, in any locality, during what may
be termed the solstitial months, namely, June and December ; and it
would appear that such herrings are never (or very rarely) taken in

* " Ueber das Kopfskelet von Alepocephalus rostralits " (" Morphologisches Jahrbuch,"
Bd. iv., Suppl., 1878).



THE HERRING. 441

May, or the early part of J^ily, in the latter part of November or the
early part of January. But a spring spawning certainly occurs in the
latter part of January, in February, in March, and in April ; and an
autumn spawning in the latter part of July, in August, September,
October, and even as late as November. Taking all parts of the
British coast together, February and March are the great months for
the spring spawning, and August and September for the autumn
spawning. It is not at all likely that the same fish spawn twice in the
year ; on the contrary, the spring and the autumn shoals are probably
perfectly distinct ; and if the herring, according to the hypothesis
advanced above, come to maturity in a year, the shoals of each spawn-
ing-season would be the fry of the twelvemonth before. However,
no direct evidence can be adduced in favor of this supposition, and it
would be extremely difficult to obtain such evidence." *

I believe that these conclusions, confirmatory of those of previous
careful observers,! are fully supported by all the e\'idence which has
been collected, and the fact that this species of fish has two spawning-
seasons, one in the hottest and one in the coldest months of the year,
is very curious.

Another singular circumstance connected with the spawning of the
herring is the great variety of the conditions, apart from temperature,
to which the fish adapts itself in pei'forming this function. On our
own coast, herrings spawn in water of from ten to twenty fathoms,
and even at greater depths, and in a sea of full oceanic saltness. Nev-
ertheless, herrings spawn just as freely not only in the narrows of the
Baltic, such as the Great Belt, in which the water is not half as salt
as it is in the North Sea and in the Atlantic, but even in such long
inlets as the Schlei in Schleswig, the water of which is quite drinkable
and is inhabited by fresh-water fish. Here the herrings deposit their
eggs in two or three feet of water ; and they are found, along with
the eggs of fresh-water fish, sticking in abundance to such fresh-water
plants as Potamogeton.

Nature seems thus to offer us a hint as to the way in which a fish
like the shad, which is so closely allied to the herring, has acquired
the habit of ascending rivers to deposit its eggs in purely fresh water.

If a full female herring is gently squeezed over a vessel of sea-
water, the eggs will rapidly pour out and sink to the bottom, to which
they immediately adhere with so much tenacity that, in half an hour,
the vessel may be inverted without their dropping out. When spawn-
ing takes place naturally, the eggs fall to the bottom and attach them-
-elves in a similar fashion, but at this time the assembled fish dart
wildly about, and the water becomes cloudy with the shed fluid of the

* " Report of the Royal Commission on the Operation of the Acts relating to Trawling
for Herrings on the Coast of Scotland, 1863," p. 28.

f Brandt and Ratzeburgh, for example, in 1833, strongly asserted that the herring has
two spawning-seasons.



442 THE POPULAR SCIENCE MONTHLY.

milt. The eggs thus become fecundated as they fall, and the develop-
ment of the young within the ova sticking to the bottom commences
at once.

The first definite and conclusive evidence as to the manner in
which herring-spawn is attached and becomes developed that I know
of was obtained by Professor Allman and Dr. JNIacBain in 1862,*
in the Firth of Forth. By dredging in localities in which spent her-
ring were observed on the Ist of March, Professor Allman brought
up spawn in abundance at a depth of fourteen to twenty-one fath-
oms. It was deposited on the surface of the stone, shingle, and
gravel, and on old shells and coarse shell-sand, and even on the shells
of small living crabs and other Crustacea, adhering tenaciously to
whatever it had falle\i on. No spawn was found in any other part of
the Forth ; but it continued to be abundant on both, the east and the
west sides of the Isle of May up to the 13th of March, at which time
the incubation of the ovum was found to be completed in a great
portion of the spawn, and the embryos had become free. On the
2.5th scarcely a trace of spawn could be detected, and nearly the
whole of the adult fish had left the Forth.

Professor Allman draws attention to the fact that " the deposit of
spawn, as evidenced by the appearance of spent herrings, did not take
place till about sixty-five days after the appearance of the herring
in the Firth," and arrives at the conclusion that " the incubation prob-
ably continues during a period of between twenty-five to thirty days,"
adding, however, that the estimate must, for the present, be regarded
as only approximative. It was on this and other evidence that we
based our conclusion that the eggs of the herring " are hatched in at
most from two to three weeks after deposition."

Within the last few years a clear light has been thrown upon this
question by the labors of the West Baltic Fishery Commission, to
which I have so often had occasion to refer.f It has been found that
artificial fecundation is easily i:)ractised, and that the young fish may
be kept in aquaria for as long as five months. Thus a great body of
accurate information, some of it of a very unexpected character, has
been obtained respecting the development of the eggs, and the early
condition of the young herring.

It turns out that, as is the case with other fishes, the period of in-
cubation is closely dependent upon warmth. When the water has a
temperature of 53° Fahr., the eggs of the herring hatch in from six to

* " Report of the Royal Commission on the Operation of the Acts relating to Trawling
for Herrings on the Coast of Scotland, 1863."

f See the four valuable memoirs, Kupffer, " Ueber Laichen und Entwickelung des
Herings in der westlichen Ostsee" ; idem, " Die Entwickelung des Ilerings im Ei " ; Meyer,
" Beobachtungen iiber den Wachsthum des Herings " ; Heincke, " Die Varietaten des
Herings," which are contained in the Jahresbcricht der Commission in Kiel fiir 1874-"76
— 1878. Widegren's essay " On the Herring," 1871, translated from the Danish in U. S.
Commission Reports, 1873-75, also contains important information.



THE HERRING. 4+3

eight days ; the average being seven days. And this is a very inter-
esting fact when we bear in mind the conclusion to which the inquiries
of the Dutch meteorologists, and, more lately, those of the Scottish
Meteorological Society, appear to tend, namely, that the shoals prefer
water of about 55°. At 50° Fahr., the period of incubation is length-
ened to eleven days ; at 46° to fifteen days ; and at 38° it lasts forty
days. As the Forth is usually tolerably cool in the month of March,
it is probable that Professor AUman's estimate comes very near the
truth for the particular case which he investigated.

The young, when they emerge from the egg, are from one fifth to
one third of an inch in length, and so extremely unlike the adult
herring that they may properly be termed larvae. They have enormous
eyes, and an exceedingly slender body, with a yelk-bag protruding
from its fore-part. The skeleton is in a very rudimentary condition ;
there are no ventral fins ; and, instead of separate dorsal, caudal, and
anal fins, there is one continuous fin, extending from the head along
the back, round the tail and then forward to the yelk-bag. The intes-
tine is a simple tube, ciliated internally ; there is no air-bladder, and
no branchiae are yet developed. The heart is a mere contractile vessel,
and the blood is a clear fluid without corpuscles. At first the larvae
do not feed, but merely grow at the expense of the yelk, which gradu-
ally diminishes.

Within three or four days after hatching, the length has increased
by about half the original dimensions, the yelk has disappeared, the
cartilaginous skeleton appears, and the heart becomes divided into its
chambers ; but the young fish attains nearly double its first length
before blood-corpuscles are visible.

By the time the larva is two thirds of an inch long (a length which
it attains one month after hatching), the primitive median fin is sepa-
rated into dorsal, caudal, and anal divisions, but the ventral fins have not
appeared. About this J)eriod the young animal begins to feed on small
Crustacea ; and it grows so rapidly that, at two months, it is one and a
quarter inch long, and, at three months, has attained a length of about
two inches.

Nearly up to this stage, the elongated, scaleless little fish retains
its larval proportions ; but, in the latter part of the third month, the
body rapidly deepens, the scales begins to appear, and the larva passes
into the "imago" state — that is, assumes the forms and proportions
of the adult, though it is not more than two inches long. After this,
it goes on growing at the same rate (eleven millimetres, or nearly
half an inch) per month, so that, at six months old, it is as large as a
moderate-sized sprat.

The well-known " whitebait " of the Thames consists, so far as I
have seen, almost exclusively of herrings, under six months old, and as
the average size of whitebait increases, from March and April onward,
until they become suspiciously like sprats in the late summer, it may



444 THE POPULAR SCIENCE MONTHLY.

be concluded that they are the progeny of herrings which spawned
early in the year, in the neighborhood of the estuary of the Thames,
up which these dainty little fish have wandered. Whether it is the
general habit of young herring, even of those which are spawned in
deep water, to migrate into the shallow parts of the sea, or even into
completely fresh waters, when such are accessible, is unknown.

In the " Report on Trawling " (1863) we observe :

" It is extremely difficult to obtain any satisfactory evidence as to
the length of time which the herring requires to pass from the embry-
onic to the adult or full condition. Of the fishermen who gave any
opinion on this subject, some considered that a herring takes three,
and others that it requires seven years to attain the full or spawning
condition ; others frankly admitted that they knew nothing about the
matter ; and it was not difficult, by a little cross-examination, to satisfy
ourselves that they were all really in this condition, however strongly
they might hold by their triennial or septennial theories. Mr. Yarrell
and Mr. Mitchell suppose with more reason that herring attain to full
size and maturity in about eighteen months.

"It does not appear, however, that there is any good evidence
against the supposition that the herring reaches its spawning condition
in one year. There is much reason to believe that the eggs are hatched
in, at most, from two to three weeks after deposition, and that in six
to seven weeks more (that is at most ten weeks from the time of lay-
ing the eggs) the young have attained three inches in length. Now, it
has been ascertained that a young smolt may leave a river and return
to it again in a couple of months increased in bulk eight or ten fold,
and, as a herring lives on very much the same food as a smolt, it ap-
pears possible that it should increase in the same rapid ratio. Under
these circumstances nine months Avould be ample time for it to enlarge
from three to ten or eleven inches in length. It may be fairly argued,
however, that it is not very safe to reason analogically from the rate



Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 55 of 110)