How can you tell the age of a fish? This question is often asked and
just so often is the answer unsatisfactory.
A fish is a cold-blooded animal; that is, his temperature is nearly
the same as that of the water in which he lives. His circulation is
sluggish and his appetite is a variable quantity. He has the capacity
to take in large quantities of food at one meal and properly assimilate
it; on the other hand he is able to fast for weeks at a time. He has
his own notions about eating, and it is quite impossible to induce him
to change them, and all this has considerable influence on his rate
of growth. It is out of the question to expect him to grow when he is
fasting; on the other hand he must draw on the fat he has stored up in
his body to furnish him energy for his muscular movements and to carry
on the ordinary functions of nutrition. The fish here has an advantage
over the warm-blooded animals, for he does not need to generate heat
to keep his body at a constant temperature. The amount of food often
eaten at one time is quite remarkable. I remember once of taking nearly
one pound of sunfish from the stomach of a Large-mouthed Black Bass.
This does not indicate that a bass must eat such meals three times each
day, it only shows his capacity to make use of a large quantity of food
when it is abundant and his stomach feels the need of it. A trout is a
good feeder; his stomach and mouth are large, much in size like that
of the black bass. From experiments conducted at Neosho, Missouri, by
Mr. Page, he found that a young trout did best on a daily ration of
solid food equal to about seventy-five per cent of its weight. On this
amount the trout would reach an average length of six inches in one
year. The average amount of solid food consumed daily by a man is from
one and one-half to two per cent of his weight, or more than twice that
consumed by our active, growing young trout. As mentioned before, the
trout is relieved from generating heat to keep his body at a constant
temperature, and at one usually much higher than the medium in which he
lives.
As an example of the ability of fishes to go for some time without
eating, we need only mention our Pacific salmon. There are five species
of these large fishes on the Pacific coast. In the early spring (April)
many of the largest species, the Chinook, start up the Columbia river
for the purpose of spawning. They reach the headwaters of the Columbia
in Idaho early in September. During this journey they eat nothing. We
know they do not eat, for of the thousands caught each year for the
canneries none are found with food in their stomachs; besides, this
organ has become much shrunken. If they did eat on this journey there
would not, I believe, be enough animal and plant life in the Columbia
to furnish each salmon with more than one meal. Now many of them make
the journey against a strong current for more than one thousand miles,
and reach an elevation of about eight thousand feet above the sea.
When they leave the ocean they are in excellent condition, by the time
they have reached their journey's end they are thin and haggard, their
vitality is so reduced that soon after spawning they die--literally
die of starvation. Their eggs hatch during the winter. By the next
winter the young salmon are from four to five inches in length, and by
the following fall or early winter they go to the sea, having reached
an average length of about ten inches. After leaving the fresh water,
which only afforded them a scant subsistence for nearly two years,
the generous ocean gives them plenty of sea room and an abundance of
food, which in a few years prepares them to repeat the long journey
of their parents. We are, in case of most fishes, ignorant of their
life histories, as we are of the salmon's. We know the average rate of
growth of the salmon for the first two years, but we know nothing more
of them until they return to fresh water to spawn.
I mentioned that trout in the Neosho Fish Hatchery grew, under
favorable circumstances, to a length of six inches in one year. It must
not be taken for granted, however, that trout six inches in length are
one year old. In their native streams, in cooler regions, they will not
often attain this length in two or more years.
In general we do not find large fishes in small bodies of water;
neither do we find the fish in our small aquaria growing at an alarming
rate. The fish disdains to outgrow his surroundings; he may feel his
importance, and consider himself in many ways superior to the other
fishes in the pond with him, but he will not permit himself to grow to
such a size as to make the question of securing a living a difficult or
irksome one.
Fishes spawn but once each year, and the time and length of the
spawning season is not the same for all species. With some species
the season is short, while with others it may extend through three
or more months. In the latter case those produced the first part of
the spawning season are at the end of six months much larger than
those which appear at the close. It is therefore evident that the
fishes of any single brood by the end of the year will vary greatly in
size, often to such an extent that the broods of one season cannot be
separated from those of the preceding season; especially is this true
of our smaller species. Mr. Moenkhaus, in making a study of the two
species of darters, the Sand Darter or "Johnny," and the Log Perch,
found by collecting a large, miscellaneous lot of these fishes, from
a given locality, that it was possible to separate them in groups
according to size of one, two or three years of age, which indicates a
quite uniform rate of growth for these two species.
Mr. Voris collected a miscellaneous lot of over five hundred specimens
of the Blunt-nosed Minnow from Turkey Lake in Indiana, varying from
one to three inches in length. These, when separated as far as
possible, according to sizes, did not fall into distinct groups of
different ages. In my own collecting and study of fresh water fishes
I have always been impressed with the difficulty of recognizing the
age of fishes, except that the smallest taken was considered to be
the product of the preceding spawning season. Here is an interesting
question to which but little attention has been given. Any one will
find much interest in studying the rate of growth of fishes under
different circumstances. We know that the rate of growth is in no way
uniform, as is the case with our warm-blooded animals. We also know
that among fishes there is no uniform adult size, as there is in case
of warm-blooded animals (birds and mammals). In general, we cannot
speak of a fish as being full-grown; at the same time there seems to be
a limit of size for each species in each body of water, beyond which
only a few go. The Chinook salmon we mentioned reach an average weight
of twenty to thirty pounds, although individuals are occasionally taken
of forty, sixty or even one hundred pounds weight. These large fishes
are by no means common, the other species of salmon never attain the
size of the Chinook.
There is an interesting family of fishes in our fresh waters known as
Minnows; these fishes are too small and too full of bones to become
a favorite for the table. They are the most helpless of all our
fresh water fishes, being soft, and, as they are slow swimmers, they
become an easy prey to larger fishes, and form a large part of their
food supply. They have been constantly driven into smaller streams
and shallow water, until they have become exceedingly dwarfed. Their
only use in the economy of fish life seems to be to assimilate small
organisms, converting them into such shape that they can be taken by
the larger fishes. Now the Minnows of all the United States east of the
Rockies are small and, except in case of a few species, they are less
than six inches in length. The predatory fishes, such as the Sunfishes
and Perches, Pike and Pickerel, are their worst enemies. In the Rocky
Mountains there are none of these fishes, and many minnows there grow
to a length of two feet or more. The only enemy of importance they
have is the trout, but the minnow finds a more congenial climate in
the larger bodies of water, too warm for the trout. The struggle for
existence has been a severe one, especially so in our streams where
species of fish are the more numerous. It has greatly limited the
growth of most species beyond an average size, and is in many places
responsible for the fact that often a species may become dwarfed in
certain bodies of water. In the Salmon river in Idaho it was not an
uncommon thing to catch trout of three or four pounds weight. In the
smaller tributaries and in the smaller mountain lakes it was unusual
to catch one weighing over one-half pound, the average being less than
one-fourth pound. I have no doubt that many of those from the small
lakes of one-half pound were as old as the large ones taken from the
Salmon river.
Fish eat and grow very irregularly. The average size of individuals,
which we would ordinarily call adults, for some species, is different
in different bodies of water. Their growth is influenced largely by the
size and depth of the body of water in which they live, also by its
temperature and the amount of suitable food it contains. The value or
extent of each of these influences is imperfectly understood.
The forms of fishes are very numerous. Some are extremely long and
slender, as many of the species of Eels, Pipe-fishes and the like,
while others are extremely short, like Sunfish of the ocean. Others,
like the Trunk Fishes, are nearly equal in all dimensions. The average
form and the one which best suits our idea of a fish, is the Black
Bass, or other fishes of similar pattern. To know the advantages of
these forms one must study the fishes in their native element. The
peculiar forms which many species take are the most noticeable in those
found in the tropics. The struggle for existence there is the most
severe, and it seems as if each species had labored to take on some
peculiar form which would assist most in its preservation. In this
respect color also plays an important factor. It is in the tropics and
among the many species of corals that we find the most highly-colored
fishes.
Many fishes have the power to change their color, and this they can do
in a very short time. The flounders are a peculiar family, the young
when born are symmetrical. Early in life they take on the habit of
their parents and lie on one side, the eye on the underside disdains to
look downwards and so begins to move toward the other side. The bones
of the head suit themselves to this change and soon our flounder has
both eyes on the same side of the head. The upper side is colored much
to resemble sand, and the under side becomes nearly white. The flounder
protects himself by covering his body, except the eyes, with sand.
Flounders live on sandy bottoms, some in shallow water, while others
are found in deepest parts of the ocean. If flounders are placed in an
aquarium and arranged so the light can fall on the under side of their
bodies, this, too, becomes dark, much like the other side.
It is interesting to study the habits of fishes in a small aquarium,
and to especially notice their ability to change color, and how rapidly
they do it. So many persons seem to be saturated with the idea that an
aquarium must have in it one or more gold fish. This seems to me to be
a mistake when our streams contain so many species suitable for the
aquarium which are far more handsome than the gold fish, and which,
if you give them half a chance, will teach you something of interest.
Mr. Ford, of Berwyn, Illinois, has a small aquarium, in his house, in
which he keeps from fifteen to twenty-six species of native fishes.
Among these are several species of Darters, the most beautifully
colored and the most interesting of all our fresh-water forms. Then
there are Minnows, Suckers, Catfishes, Sunfishes, the Pike, Mud
Minnow, Top Minnow, and so on. To one who would know fishes, any one
of these species is more desirable than gold fish. The study of fishes
in an aquarium, such as the one possessed by Mr. Ford, is extremely
interesting. They will teach you much about their habits, besides
giving you many lessons showing their ability to change color and adapt
themselves to their surroundings.
[Illustration: A MOUNTAIN LAKE.
CHICAGO:
A. W. MUMFORD PUBLISHER.]
The Blind Fishes, which inhabit caves in this country, are very
interesting. They have lost their color, if they ever had any, being
white. In many the eyes have become so degenerated as to be entirely of
no service when the fish is in the light. The head is furnished with
tactile organs, which enables them to feel their way in the dark. In
fact, they are well adapted for the life they lead. Dr. Eigenmann tells
us that Blind Fishes were not accidentally swept into caves or driven
there by their enemies, "but entered them deliberately and avoided
coming out into the light." In other words, they preferred "darkness
rather than light." Having simplified eyes and highly developed sense
organs, they were able to live in the dark. The many ages they have
lived in the caves has better fitted them for their existence in total
darkness. The Blind Fishes were not always blind, but have become so
because of their own preferences.
The readers are, if they will only study fishes, sure to find them
extremely interesting. There are a wonderful variety of fishes, each
well adapted for the life it leads. You will find them in the brooks,
creeks, rivers and lakes or ocean, wherever you happen to be, and you
are sure to be highly repaid for all the study or attention you may
give them.
Seth E. Meek.