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generation of eels it would seem, so far as we are at present aware, that the
presence of salt water is a necessity, for it has been observed that when these fish
leave rivers and brackish waters for the sea, their reproductive organs have
scarcely begun to develop. But their maturing in the sea must be rapid, because
in five or six weeks they have arrived at a breeding condition. This rapidity of
maturing in the breeding-organs would seem to be the cause of extreme exhaustion.
Consequently, after the breeding-season is over, eels die, similarly to lampreys and
i '( -veral other piscine forms; and this furnishes the explanation why, subsequent
to this period, old eels are not observed reascending rivers." After describing the
appearances of the reproductive organs in fully-developed eels of both sexes, as well
as those of sterile individuals, Day observes that " it becomes necessary to allude
to the localities in which each of these forms may be found. Here, again,
imagination seems to have mixed up fact with fiction, and it has been maintained
that should very young eels be introduced from the mouths of rivers into inland
pieces of water, they invariably develop into fish of the female sex, as it was
supposed males were never to be seen in fresh water. Whether such waters are
really conducive to the destruction of young male eels, appears to be a subject
requiring further elucidation. The female eels are those usually captured when
descending towards the mouths of rivers during the autumn months, while such
as are developing towards a breeding condition do not seem to feed at these,
periods. Males have been usually obtained from the mouths of rivers or in
brackish waters; and Dr. Paul, having discovered that among elvers, or young
eels, captured in such localities were males, ascertained (at least so he asserts) that
when transported to fresh waters, they retained their masculine character, develop-
ing into adults. Some have been captured ten or twelve miles up rivers ; but,
although male eels undoubtedly ascend rivers, their proportionate number to that
of females decreases in accordance to the distance from the sea. Sterile eels are
found in fresh waters, and likewise in those which are brackish, where they may
often be captured feeding, but these fish, of course, cannot increase in numbers
unless they have access to the sea, and consequently above impassable barriers
they die out, should no young be introduced. The migrations of these fishes may
be said to be two annually, adults descending seawards to breed, as they do in the
Severn, about the month of September, although this migration in Norfolk is
asserted t,o begin as early as July. There is likewise an up-stream migration of
young eels, or elvers, in the earlier months of the year up to May or June, or even
later; during this period the banks of .the rivers being in places black with these
migrating little fishes. These young eels have been observed to ascend floodgates
of lochs, to creep up water-pipes or drains; in short, mechanical difficulties scarcely
obstruct them, and they will even make a circuit over a wet piece of ground in
order to attain a desirable spot." In order to give some idea of the vast numbers
of young eels that take part in these migrations, or, as they are popularly called
"eel-fares," it may be mentioned that upwards of three tons of elvers were dis-
patched in a single day from the Gloucester district in the spring of 1886, and
that it has been calculated that over fourteen thousand of these fish go to make a
pound weight. In the previous year the annual consumption of eels was estimated



EEL TRIBE. 449

at a minimum 1650 tons, with a total value of 130,000. It is almost superfluous
to mention that eels pass the greater portion of their time when in fresh water
buried in the mud, from which they issue forth at night to feed. During the cold
of winter large masses of them are not unfrequently found tightly coiled together
for the sake of mutual warmth. The largest species occur in the islands of the
South Pacific and New Zealand, where they inhabit lakes ; specimens from these
regions having been recorded to measure from 8 to 10 feet in length.

Resembling the true eels in the presence of pectoral fins, in the

tail being surrounded by the median fin, and the free tongue, the
gigantic marine forms known as congers differ in being scaleless, in the deep cleft
of the mouth, in the presence of a set of teeth on the outer sides of the jaw placed
so close to one another as to form a cutting edge, and by the dorsal fin commencing
at a point just behind the base of the pectorals. The common conger (Conger
vulgaris), which may grow to a length of 8 feet, appears to be' almost cosmo-
politan in distribution, being as abundant in the seas of Tasmania as it is in
British waters. Congers feed chiefly by night, and prey upon crustaceans, cuttles,
and various kinds of fish, such as pilchards and herrings. Their favourite resorts
are either hollows or crevices in the rocks, or sandy bottoms, in which they can
bury themselves ; and in such situations they are sometimes left by the ebbing
tide. The flesh of these eels is of a highly gelatinous nature, and is said to be
largely employed in soups. Three other species of the genus are known, one of
which is abundant in the Indian Ocean.

Among the numerous other generic modifications of the family,

we select for notice the serpent-eels (Ophichthys) as an example of a
group in which the extremity of the tail is free, the nostrils are situated at the
extremity of the muzzle, and the tongue is fixed. Teeth are present on the
vomers, those in the jaws being either obtuse, or pointed and arranged in a single
series ; and whereas small pectoral fins are present in some species, in others they
are wanting. Serpent-eels are represented by a great number of species, ranging
over all tropical and subtropical seas, but none attaining any large size. The
difference in the structure of the teeth of the various species may probably be
taken as indicative of a difference in the nature of the food similar to that already
recorded as obtaining among the mursenas.

Only a few words can be devoted to the deep-sea members of

the family, which are represented by several genera. Among these
are certain congers (Syno^liobranchus) occurring in all oceans at depths of from
three hundred and forty to two thousand fathoms, and characterised by the gill-
openings being united into a single longitudinal slit on the under surface of the
body between the pectoral fins ; the gape being very wide, the teeth small, and the
body scaled. In these forms the muscular system is well developed ; but in another
genus (Saccopharynx) it is extremely feeble, except on the head, and the bones
are soft and spongy, The head and gape are of immense size ; the muzzle is short
and flexible ; the weak jaws are armed with long, slender, curved teeth, placed at
intervals ; and the gill-openings are wide and situated on the lower part of the
sides at some distance from the head, the narrow gills being free and exposed.
The long and band-like tail ends in a long tapering filament, and the dorsal and

VOL. V. 29



45



TUBEBLADDERED GROUP.



anal fins are rudimental. As in the last genus, the stomach is capable of great
distention, and specimens which had swallowed fish of many times their own
weight have been found floating in the Atlantic with this organ dilated to its
utmost. In a third type (Nemichthys), from depths between five hundred and two
thousand fathoms in the Atlantic, the exceedingly elongate body is band-shaped,
with the tail tapering to a point, and the jaws produced into a long slender beak.

It has been already noticed that in one of the deep-sea eels the
gill-openings are confluent into a longitudinal slit on the under
surface of the body ; and a very similar condition characterises the second family
(Symbranchidce) of eels, only in this case the slit is transverse. A better dis-
tinction is, however, afforded by the structure of the upper jaw, the margin of
which in the present family is formed entirely by the premaxillas, on the inner
side of which lie the maxillae The paired fins are rudimental, and the vertical



Single-Silt Eels.




HKXC.VL SHORT -TAILED EEL (J liat. Size).

ones wanting . while the scales, if present, are minute ; and accessory breathing-
organs may be developed. An air-bladder is wanting, the stomach has no blind
appendage, and the ovaries are furnished with ducts ; the vent being situated far
behind the head. Whereas the majority of these eels inhabit fresh and brackisl
waters in tropical Asia and America, they are also represented in Australia, whei
one genus is marine. Of the fresh-water forms, the most remarkable is th(
amphibious eel (Ampkipnous cuchict) of Bengal, in which there is an accessoi
breathing-apparatus, the body is scaled, and the pectoral girdle is detached from tlu
skull. There are only three gill-arches with rudimentary lamina 1 , separated froi
one another by narrow sliis; and the additional breathing-organ takes the form
a lung-like sac on each side of the neck communicating with the gill-chamboi
Day states that "this amphibious fish, when kept in an aquarium, niav
observed constantly rising to the surface for the purpose of respiring atmospheric
air direct. It usually remains with the snout close to the surface, and in like
manner lies in ihe grassy sides of ponds and siagnant pieces of water, so that



EEL TRIBE, 451

without trouble it may obtain access to air." Indeed, the chief respiration of
this fish is carried on by means of the two sacs on the sides of the neck, which
can be inflated and emptied at will. In the other two fresh-water genera, one of
which (Monopterus) is confined to the Oriental region, while the other (Symbran-
ckus) has a distribution coextensive with that of the family, there is no additional
breathing-organ, the body is naked, and the pectoral girdle is attached to the
skull. Whereas in the former of these genera the gills are rudimental, in the
latter they are well developed ; and, in the absence of an accessory apparatus, it
seems strange how the one species with rudimental gills manages to breath at
all. The Bengal short-tailed eel (Symbranchus bengalensis) has been selected to
illustrate the external form of the members of this very remarkable family.




Together with four other genera from the fresh waters of Tropical
America, the well-known electric eel (Gymnotus electricus) constitutes
the third and last family of the group under consideration, the leading charac-
teristics of which are as follows. The jaws are formed in the same manner as in
the true eels, and the head is scaleless and without barbels. The dorsal fin is
either totally wanting, or reduced to a fatty rudiment; the anal is extremely
elongated ; pelvics are wanting ; and the caudal is likewise generally absent, the
tail terminating in a point, which, when broken off, can be renewed in the same
manner as in the; blind-worms. The vent is situated in or near the throat ; the
gill-openings are rather narrow; an air-bladder is present; the stomach has a
blind appendage ; and the ovaries are provided with ducts. In the skeleton the
pectoral girdle is attached to the skull. By Professor Cope the typical genus is
considered to be to a certain extent intermediate between the last family and the
eel-like representatives of the cat-fishes.



452 TUBE-BLADDERED GROUP.

As a genus, the electric eel is characterised by the absence of the caudal and
dorsal fins, by the anal extending to the extremity of the tail, the absence of scales,
the single series of conical teeth, and the minute eyes. Abundant in the rivers
and lagoons of certain parts of Brazil and the Guianas, the electric eel grows to a
length of fully 6 feet, and is capable of giving a more powerful shock than any of
the other fishes endued with electric power. It will be unnecessary to give any
description of the electric organs here ; and it will accordingly suffice to mention
that they form two pairs of longitudinal structures lying between the skin and the
muscles ; one pair being situated on the back of the tail, and the other along the
sides of the base of the anal fin. That these organs are capable of giving .shocks
sufficient to kill other fish and small mammals is undoubted ; but Dr. Glinther
considers that the description by Humboldt of the capture of electric eels by horses
driven into water, in order to receive the shocks and thus exhaust the fishes, seems
to be the result of the imagination of some person who related the supposed
incident, or to rest on some isolated incident, since no recent travellers to the
district have found evidence of the existence of the practice.

SECTION NEMATOGNATHI.
THE CAT-FISHES OR SHEATH-FJSHES, Family SILURIDSE.

Although represented only by a single European species, and that confined to
the rivers to the eastward of the Rhine, the great family of cat-fishes is one of
extreme importance in tropical and subtropical countries, its members being extremely
abundant in the fresh waters and estuaries of the Oriental region, as they are in
those of South America. An essential characteristic of the family is the invari-
able absence of scales, the skin being either smooth or covered with bony tubercles
or plates ; and this character, together with the presence of the barbels from which
they derive their popular title, will always serve to distinguish the cat-fishes from
the other great fresh-water family of the carps. In the skull an essential feature is
the absence of a subopercular element to the gill-cover ; while the margin of the
upper jaw is formed mainly by the premaxillas, the maxillas being more or less
rudimental. A rayed dorsal fin may be absent, but the fatty dorsal is generally
present; and when an air-bladder is developed, it may be either free in the
abdominal cavity or enclosed in bone, but always communicates with the ear by
the intervention of the auditory ossicles, which are somewhat lenticular in form.
The skull is characterised by the full ossification of its lateral region, the septum
between the eyes being also bony ; and in many instances the skull is prolonged
backwards by the development of a kind of bony helmet over the nape of the
neck, formed by dermal ossifications overlying some of the bones of the pectoral
girdle. Frequently this shield, as well as the hinder bones of the skull, are
ornamented with a tuberculated sculpture. Many of these fishes have also a
powerful spine at the front of the dorsal fin, which can be locked into a fixed, erect
position by a rudimental spine acting as a kind of bolt at its base, and is itself
articulated to the vertebrae, and also joined by a ring to a second spine, in a manner
similar to that obtaining in the angler-fish. To support this spine certain special
modifications exist in the structure of the pectoral girdle. Some of the genera,



CAT-FISHES. . 453

such as the one represented by the eel-like cat-fish, have additional breathing-
organs ; in this particular instance taking the form of a branched structure attached
to the gills. On the other hand, in the sac-gilled cat-fishes (Saccobranchus), there
is a long sac running down the muscles of the back behind the proper gill-chamber.
Through this breathing-sac blood is carried from and returned directly to the
heart ; and in consequence of this arrangement these fishes can remain alive for
hours or even days apart from water, so that they are able to traverse spaces
where aquatic respiration is impracticable. Among the Indian representatives of the
family it is somewhat curious that whereas most of the forms dwelling far in the
interior of the country near and in the hills have the air-bladder ossified, this is
not the case with those inhabiting the rivers of the plains and the sea. The
majority of the cat-fishes are inhabitants of the fresh waters and estuaries of the
tropical and subtropical regions of the globe ; but, as we have seen, one species is
found in those of Eastern Europe, while a considerable number enter the sea,
although generally keeping near the coasts. They are found not only in rivers,
but likewise in lagoons and marshes. Day writes that " they mostly prefer muddy
to clear water, and the more developed the barbels the more these fishes appear to
be adapted for an inland or muddy fresh-water residence. The wider and deeper
the rivers, the more suited they are for the Siluridce, consequently the larger forms
are comparatively rare in the south of India, whilst they abound in the Indus,
Jumna, and Ganges, as also in the Irawadi and other Burmese rivers." It may be
added that they are equally common in the muddy waters of the La Plata River.
" Owing to their usual resort," continues the same writer, " these fishes appear to
employ their feelers in moving about in muddy places, and consequently have less
use for their eyes than forms that reside in clear pieces of water. This is one
reason why the size of the eye as compared with the length of the head is much
greater in the young than in the adult. The eye, in fact, atrophies, instead of
increasing in size in proportion with the remainder of the head. In some species
the skin of the head passes over the eye without any trace of a free orbital margin.
In the genus Arius, and some allied marine forms, the males appear to carry their
ova in their mouths, perhaps until the young are produced. Many of these fishes
are credited with causing poisonous wounds, and we frequently find such cases
admitted into hospitals. The injuries may be divided into two classes, namely, those
in which the wounds are of a distinctly venomous description, and those in which
the jagged spines occasion intense inflammation, often of a dangerous character."
The flesh of the cat-fishes is of an inferior quality, and generally eaten only by the
lower classes. All the members of the family are very tenacious of life, and
extremely difficult to kill. Geologically cat-fishes date from the lower Eocene
London Clay, where they are represented by the extinct Sucklandium, apparently
allied to an existing African genus ; while in the higher Eocene of the south of
England there occur species referred to the existing genus Arius, An extinct
genus has also been described from the Eocene of North America; and in the
Eocene of Sumatra, as well as in the Pliocene of India, the fossil forms belong to
existing genera, and some of those from the latter deposits even to species still
inhabiting the same country. Numerically the cat-fishes form an exceedingly
large family, the existing types constituting considerably over a hundred genera,



454 . TUBE-BLADDERED GROUP.

many of which contain a multitude of species. In this work only a very few
of the genera can be even mentioned, some of those selected including the largest
members of the family.

Clarias anauillaris is a well-known representative of the first
Eel-Like Cat-Fish. ,..,.,., i i i u i

subfamily, in which the long dorsal and anal tins extend nearly

throughout the length of the trunk. It belongs to a minor group confined to
Africa and the Oriental region, and characterised by the dorsal fin being either
composed of weak rays throughout its length, or with its hinder portion modified
into a fatty fin.

The wcls (Silurus glanis), shown in the larger figure of the
illustration on p. 436, is the typical representative of the second
subfamily, in which the rayed dorsal fin is but little developed, and if present at
all occupies only the hinder region of the trunk ; the fatty portion being small or
wanting. The anal fin is not much shorter than the caudal region of the backbone,
and the pelvic fins are behind or below the dorsal. In the wels and its congeners the
short dorsal has no pungent spine ; the fatty fin is wanting ; there arc two upper and
two or four lower barbels ; the head and body are naked : and the tail-fin is rounded.
The wels itself, which is confined to the European rivers eastwards of the Rhine,
has six barbels, of which the upper pair are considerably longer than the head, and
commonly attains a length of from G to 9 feet, although it occasionally grows to
13 feet. In colour the head, back, and edges of the fins are bluish black, the sides
greenish black spotted with olive-green, and the under-parts reddish or yellowish
white with blackish marblings. Frequenting rivers and lakes with muddy
bottoms, the wels feed on fishes, frogs, and crustaceans, but it will also sei/e and
pull down ducks, geese, or other birds swimming on the surface. The spawning-
time is in the middle of summer, when these fish resort to the shallows in order
to deposit their eggs on the stems and leaves of water-plants.

Yarreii's Cat- Another gigantic species is Yarrell's cat-fish (JB(jrinH yarretti),

Fish, etc. from the large rivers and estuaries of India and Java, which attains
a length of fully 6 feet, and from its huge head and mouth is one of the ugliest
fishes in existence. The only member of its genus, it belongs to a subfamily in
which the rayed dorsal fin is short, and situated in the hinder part of the body in
advance of the pelvics; and there is always a fatty fin, which may. however, be
short: and the anal is shorter than the caudal region of the backbone. When
nasal barbels are developed, they belong to the hinder nostrils. In the group of
genera to which Yarrell's cat-fish belongs the front and hinder nostrils are placed
near together, with a barbel between them; and in this particular form there are
eight barbels, and the upper surface of the head is naked. This gigantic species is
of especial interest on account of its fossilised remains occurring in the Pliocene
deposits of the Siwalik Hills in North-Eastern India.

The well-known genus Ai-!x, from all the tropical regions of the world,
belongs to another group of the same subfamily, in which the front and hinder
nostrils are close together, but have no barbel, although the hinder-pair are provided
with a valve. The Tropical American genus Pimeforfug is the typical representa-
tive of a third group of the same subfamily, in which the two pairs of nostrils are,
equally devoid of barbels, but are placed at a considerable distance apart. The



CAT- FISHES. 455

largest species is the leopard cat-fish, or suravi (P. pati\ from the rivers of
Argentina and Uruguay, growing to a length of 6 or 7 feet, and having the
yellowish skin marked with a number of black spots, like a hunting-leopard.
Somewhat curiously, this genus is represented by two outlying species from West
Africa. The best known representative of the fourth and last group of genera in
this subfamily is the bay ad (Bagrus bayad) of the Nile ; the group being easily
recognised by the circumstance that while the two pairs of nostrils are remote from
one another, the hinder have barbels. Both species are confined to the Nile, but
the allied Chrysicthys ranges all over Tropical Africa, and Macrones and Rita
are Oriental forms. In these forms the short dorsal fin has a pungent spine, and
the head and neck are generally protected by a tuberculated bony shield.
Electric Cat- On account of the property from which they derive their name

Fishes. brief mention must be made of the electric cat-fishes (Malapterurus)
of Tropical Africa, belonging to a subfamily in which the rayed dorsal fin, when
present, is short and confined to the hinder region of the body, while the pelvic fins
are inserted behind. From their allies these fishes are distinguished by the total
absence of the rayed dorsal, so that they have only a fatty dorsal immediately in
front of the tail (which is rounded), and opposite the anal. The head and body are
smooth, the pectoral fins have no spine, and there are six barbels. The species
inhabiting the Nile grows to about 4 feet in length.

Mailed Cat- The only other members of the family, which space admits of

Fishes. mentioning, are the mailed cat-fishes (Callichtkys, Loricaria, etc.),
constituting a subfamily mainly confined to Tropical and South America, although
represented by a few Oriental forms. In all these fishes there is always a rather
short rayed dorsal fin, beneath or in front of which the pel vies are generally
inserted. The gill-membranes are confluent with the skin of the isthmus, and the
gill-openings constricted to small slits. The pectoral and pelvic fins are placed
lorizontally ; and the vent is in front of, or only slightly behind, the middle of the
length of the body. Among these fishes the species of the genus Callickthys,
rhich are confined to the rivers on the Atlantic side of South America, belong



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 48 of 62)