This section is from the book "The Goldfish And Its Systematic Culture With A View To Profit", by Hugo Mulertt. Also available from Amazon: The goldfish and its systematic culture.
" Nature my school, the water my field."
Before we enter into the details of the propagation of the fish, it is necessary to learn something about its anatomy.
A study of the accompanying cut (which is merely diagramatic) will greatly assist the reader in getting a clear understanding of the internal arrangement of the several parts with which it is most necessary to be familiar.
We will consider first the scales, as they are almost the first thing to strike the eye. These scales are so arranged upon the surface of the body that they overlap each other just in the manner that a carpenter lays shingles on a roof, being disposed in such a way that the friction incident upon the movement of the fish in the water is reduced to the smallest proportion. As the fish grows older and larger the scales increase in size.
Near the middle of the body and running along each side of the fish, there is a line or row of scales that possess peculiarities distinguishing them from other scales.
These scales are pierced with a tubular aperture, and the tubes of which they are the exit are quite distinct, and form the so-called "lateral line." Through these tubes a slimy substance or mu-cous is exuded, which covers the entire body, seemingly for the purpose of making the fish waterproof and of further reducing the friction in the water. These tubes always point from the ma-trix, or root of the scale, towards the tail of the fish. It is scales of this description that naturalists refer to when seeking to learn the species to which the fish belongs, because the peculiarities of their structure differ in them. (See illustration.)
The next thing most noticeable are the fins, these being named according to their location upon the body of the fish and subserve various purposes. The pectoral fins (fig. a.) are those situated in the place corresponding with the fore-legs of animals, the ventral fins (fig. b.) being placed where the hind-legs of animals are found. The dorsal fin (fig. c.) is that one found upon the back of the fish. That fin situated behind the anus receives its name from that part, and is known as the anal fin (fig d.), while the tail of a fish is properly called the caudal fin, (fig. e.)
Scale From Lateral Line. (Enlarged.)
The water in which the fish lives is very nearly as heavy as the fish itself, the latter then requiring comparatively little strength to move about. The motion necessitating the greatest expenditure of power is that of propulsion forward, and is accomplished by the action of the caudal fin. The pectoral fins are used to change the water in the neighborhood of the gills, thus serving as adjunct respiratory organs. •
The ventral fins are mainly useful as a brake when the fish wishes to come to a sudden stop when in motion, or for a backward movement; the dorsal and anal fins serve the purpose of balancing the body.
The gills, which are organs of respiration, are situated on each side of the head, protected by "opercles" or gill-covers. (fig. f.) The gills themselves consist of bony arches which are covered with a tissue containing a large number of blood-vessels. As a rule there are four of these arches on each side of the head. The life-giving principle that supports animal life is a gas called oxygen, and as this exists in the water, the function of the gills is to extract it. When the water passes through them, as it does when taken in by the mouth of the fish, and is pressed through the gills, it comes in contact with the blood-vessels, the oxygen being absorbed into the blood for the nourishment of that fluid and the body generally.
It will thus be seen that it is not the water that the fish breathes, as many suppose, but the air contained in it, as can be proved by placing fish in water from which the air has been taken, by prolonged boiling or otherwise.
Fish that are kept in a vessel will come up to the surface where the air can be mixed with the water when that in the water of the vessel has become exhausted. It would seem from the fact that as the fish breathes only the air and not the water, that it could just as well live in the open air, where it could get plenty. Such is not the case, however, for the gills are so constituted by nature that they need something to keep them apart, so that their surfaces may be exposed and perform their functions properly, otherwise they would close together, the blood-vessels would cease to absorb the oxygen, resulting, of course, in the death of the fish. It is necessary, then, that a stream of water should constantly flow through them, as it does, the absorption of oxygen then going on as nature intended.
The heart of the fish lies just behind the head and between the gills (fig. g.). It is a muscular organ consisting of three parts, an auricle, a ventricle, and an arterial bulb. The venous or stale blood is pumped into the gills by the heart, where it receives a fresh supply of oxygen. From the gills it is sent to an arterial trunk, lying along the under side of the vertebral column, (fig. h.) from which it is distributed all over the body of the fish.
As fish have no lungs, they can not possess a voice.
The goldfish is supplied with a divided air-bladder (fig, i. i.) which can be filled or emptied at will. This bladder is a sac formed of a tough membrane, and is situated between the spinal column and the stomach. (fig. k.)
It appears that the air-bladder is either for the purpose of increasing the weight of the fish when empty, and decreasing it when full, thus exercising a modifying influence upon the weight of the fish when compared with that of the water.
The eyes of the goldfish are well developed, but so far as hearing is concerned, opinions differ, and the question is still disputed. It may be stated that if fish hear at all, it is with great difficulty.
It is the custom in some places where fish are kept to call them to their feeding place by the tolling of a bell, and they come, but it is a question whether they come because they hear the sound, or that they see the motion of the person ringing the bell, or that of the bell itself; this, then, can not be cited in proof of the theory that they hear.
Music or the report of firearms does not affect them at all, but the flash from the discharged gun will scare them.
Do fish sleep? Yes.
In the act of sleeping they do not close the eyelids, for the very good reason that they have none; neither do they select the night for the purpose. Goldfish have been seen asleep in the broad sunlight of the forenoon, and the same varieties have also been found sleeping at midnight. Their time for resting then, does not occur at stated periods, but whenever the desire comes upon them. The fish may very easily be observed in slumber, remaining perfectly still, the only motion being that of the breathing apparatus and the pectoral fins, the action being very slow but regular. All the other fins are at rest, and the pupils of the eyes appear to be drawn back. The other senses taste and smell are very well developed.
We come now to the consideration of the process of reproduction. The organs for this purpose are distributed between two individual - the male and the female. The female organs consist of two sacs located immediately below the spinal column on each side of the air bladder, uniting towards the posterior end in a single oviduct which discharges outside, behind the anus (fig 1.). These contain the eggs by thousands and which increase in size when the spawning season arrives, greatly distending the ovarian sacs. The ripe egg when it separates from the ovary, passes through a tube (the oviduct) (fig. m,) the opening of which, as before stated, is outside, immediately behind the anus. (fig. n.)
In the male fish the spermatic organs which are located the same as the sacs in the female, secrete a thick white fluid which contains innumerable small organic bodies, which when discharged and in a fresh condition, move about, enter the egg, impregnate it and start the development of the embryo. These bodies which are called spermatazoa, consist of an anterior thicker part, the so-called head, and the more attenuated part or tail. In the water these little organisms can live but one or two minutes but when taken from the fish and placed in a bottle kept at a proper temperature, they may be preserved alive for six days. This discovery was made by a Russian fish culturist in 1856 and is very important to the artificial propagation of fish as it enables the crossing of different species.
The eggs when first spent in the water have the shape of a slightly pressed in rubber ball, and as soon as they come in contact with liquid, they expand and suck it in through a microscopically small hole. (See illustration.) The spermatic germs of the male being present in this liquid are thus introduced and fertilize the egg.
A - Spermatic Corpuscle. B - Germinative Disk. C - Nutritive Yolk.
The fecundation of the egg consists in the entry of the spermatic corpuscles and the subsequent production of a subdivision of the germinative disc, which phenomenon is called the process of "segmentation" or "furrowing." This is followed by a series of successive changes, of which the final result is the embryo, which, subsisting or being nourished by the yolk, gradually develops into the perfect fish.
The young fish when first hatched is supplied with a sac called the yolk-bag, from which it derives its nourishment during the early period of its independent existence. When this has been exhausted it is then ready to seek other food and this it finds in various microscopic organisms that exist in profuse abundance in the water. As the fish grows larger and gains strength, other and coarser food is sought and devoured.
Fertilization of Fish Egg.