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.
"In the morning sow thy seed," says Solomon: - This advice of the Sage of the East has many applications to the affairs of every day life, and amongst other things it may well apply to the subject under consideration, not in its literal sense, but in the spirit of the admonition. As the early morning is the best time to sow seed, so is the morning of the season the best time to spawn the fish, as they are then in their best condition for that process, and besides the young will have a much better opportunity to grow without molestation, their most inveterate enemies not appearing until after the season is further advanced. Thus it is that a greater percentage survives, which, becoming marketable before the main crop arrives, bring higher prices and give the culturist encouragement by a quick return upon his labor and capital.
Again our quotation hits the mark, for the earlier the spawn is taken from the bed the greater will be the reduction of losses, as by leaving it exposed, the spawners themselves devour it.
The early morning is the favorite time for the goldfish to spawn, though it is sometimes kept up until noon. The fish are seen chasing each other and rolling over the material thrown into the water for that purpose. Upon inspection of the loosely floating clumps of roots, we discover that they have adhering to them a great many small round watery-white, creamy or yellow colored balls about the size of a pinhead; these are the eggs of the goldfish. The bunches of roots are then carefully removed from the water, and the individual rootlets bearing the eggs are either cut off with a knife or pair of scissors, or they may be detached with the thumb-nail. Great care must be taken not to disturb the eggs or injure them in any way while detaching the rootlets. They are then placed in a one-gallon candy jar, filled with clear water of the same temperature as that of the bed. Such a jar is best not over-crowded, about one hundred eggs being as many as that capacity can safely and conveniently carry, the object being to give the young fish, when hatched out, plenty of room, both to move about and obtain sufficient fresh water for respiration. When the jars have received their quota of eggs, they are taken into the house or put into some other convenient place selected for the purpose, but in such a situation that they will constantly be under close supervision.
'It is best to set them near a window, within the reach of the morning sun, there to remain untouched until the eggs are hatched.
The time required for the hatching varies from two (2) to six (6) days, it taking place most rapidly in warm weather. The temperature of the water, most advantageous for the hatching is between 6o° F., and 900 F., more or less is dangerous.
This method of caring for the eggs secures to them a more effective guard against enemies, as well as muddy water, heavy rains, and hail storms, all of which would militate against them if hatched in the open air and in the ponds. The candy-jar system furthermore recommends itself for the hatching of the eggs in this, that the whole process is under complete control and offers every facility for close inspection at all times. The jars can be obtained anywhere, are cheap, and are very convenient to handle, in short, just the thing for the purpose. For convenience of study, the marking of dates, names of varieties, etc., together with any notes that it is desired to make, a piece of paper can be pasted upon the outside of the jar, it will always be there, and the record kept upon it can always be seen at a glance.