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.
(Carassius auratus.) Der Goldfisch. Le poisson rouge.
The goldfish belongs to the carp-family, and by some authors is called Cyprinus auratus, which means gold-carp. A thorough investigation of the subject has led the author to the adoption of the name used in the heading, which is also used by some other authors. Besides being more correct, according to the anatomical structure of the fish, is more distinguishing, as there exists a variety of the European food-carp, known as the golden carp, or cyprinus aureus, which is in no ways identical with the goldfish carassius auratus.
The body of the fish is elongated, compressed upon the sides and entirely covered with a coat of uniformly-sized scales.
The head is short, naked, that is, without scales; the lips well developed and without barbies.
The color is generally an orange-yellow with a golden hue, sometimes marked with white or black; the abdomen may be either white or yellowish.
The name of the entire family, of course, had its origin in the prevailing golden color of the species first introduced into Europe.
The dorsal fin is long, reaching from the middle of the back nearly to the tail; specimens with a short dorsal fin are deformed.
They may sometimes have a divided tail, giving to them, if viewed from behind, the shape of a reversed letter "Y."
The size of the goldfish varies according to the locality in which they are raised, and the circumstances surrounding them, it being possible for them to attain a length of eighteen inches and a height of six inches. It is said that they may live to be a hundred years old, but this may be an exaggeration.
Goldfish enjoy a warm temperature, in bodies of water without a current; just such water as ponds afford suit them best, though they will make themselves at home in streams and multiply exceedingly. They are very hardy, and thrive well under circumstances that would be fatal to many other fish, this quality particularly adapting them for life in the aquarium, specimens having been successfully kept in this way, in good condition and health, from ten to sixteen years. So far as food is concerned, the goldfish will feed upon almost all kinds of vegetable matter, insects, worms, etc., even preying upon small fish, and devouring its own spawn and young. The food is taken in by a sucking motion of the lips; the mouth being toothless, as in all carps, the mastication is accomplished by a few bony tubercles situated in the throat.
In the spring or summer following the one in which they were hatched, goldfish attain their maturity. The size of the fish has nothing whatever to do with the ability to spawn, though a large fish will deposit more eggs than a small one. As an instance, goldfish one inch in length, nine months old, spawned in an aquarium kept in a parlor; all the eggs hatched and the young grew up. In the spring of that year, when the temperature of the water rises above 6o°F., they become lively and vivacious, losing all timidity and precaution, so that they easily fall a prey to their many enemies.
Two, three or more male fish follow a female, chasing her to some shallow place where there is an abundance of water-plants.
They lash the water in a lively way, twisting the posterior portion of their bodies energetically and shooting through the water near its surface with short tremulous movements of the fins. At places they gather together in a compact mass, one tumbling over the other. This is the moment when the female drops her eggs, which are immediately impregnated by the males.
This process is repeated throughout the summer, with intervals of rest during the hottest period. The eggs are of the size of a pin-head, and may be either semi-transparent, yellowish, or brilliant yellow in color. Whether this difference in the color of the eggs has anything to do with the coloring the fish will acquire after it is hatched still remains an open question. With the eggs of the trout the case is different, for the culturist can predict the color of the flesh of the fish when grown up; it is possible that this may also apply to the goldfish. The eggs are covered with some adhesive substance, mucus probably, and adhere to anything they happen to touch. The water-plants in the immediate vicinity of the place where the fish have been rolling about will, upon examination, be found covered very profusely with them.
The young are hatched out in from two to six days, the period of incubation being determined by the temperature of the water and the condition of the weather. Direct sunlight has the effect of hastening the process.
During the first few days the young fish are not able to move about much; they hang or lay about among the water-plants, obtaining subsistence from their yolk-bag, but as soon as this is absorbed they swim around on the search of something to eat.
The color of the skin of young goldfish is at first silvery gray, but at an age of six weeks this color begins to change, becoming darker and assuming a cloudy appearance, finally taking on the permanent color. The whole process is sometimes completed in two days, though in some instances it is deferred until the following spring.
The perfection and rapidity of the coloring process depend upon several causes, foremost among which is the proper selection of specimens from which to breed.
This is a very important consideration, in truth, the prime factor upon which hinges the character of the result.
When hatched, the young fish are further subjected to modification by their surroundings, the temperature of the water, its depth, quality, etc., all exercising more or less influence.
The complete result of the breeding, so far as the coloring is concerned, can not be seen until the change has taken place, when any errors that have been made are at once apparent. Those fish that have failed to receive any coloring are then called silver-fish; should they have turned milky white (albinos), they are known as pearl-fish.
The young, when kept in warm ponds - this means that the ponds are so located that the sun can warm them thoroughly - may grow six inches long in four months. As a general thing, however, the length reached in that time is from two and a half to three inches.
In connection with this may be mentioned that all the young of the same spawning do not grow at an equal rate, some few doubling the average size, while others fail to reach it. The latter are then known as dwarf goldfish, and are much in demand for small aquaria.
Deformities occur oftener in this family of fishes than in any other. Specimens minus a dorsal, anal, or even caudal fin, are frequent; rarer are those destitute of scales or minus an eye or with a lob-sided mouth.
From the habit of the goldfish to seek its nourishment on the bottom of the pond in which it lives, and to its careless sluggishness, caused by its voracious appetite, the goldfish, especially in its younger days, falls the victim of innumerable enemies.
In fact, so easy is it to destroy them, that anything else living in its company in the pond and of sufficient strength to master it, may be set down as its enemy.
When arrived at maturity its peculiar mode of reproduction renders it a welcome prey to enemies that do not live in water. It is likewise subjected to diseases of various kinds, and considering all that, it may be said that it is a mere accident when goldfish multiply to any considerable extent without the protection of man, or that the circumstances under which they increased were exceptionally favorable.