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.
For the purpose of taking the fish from the ponds, the water in the latter is drained off. But before this is done two or more large-sized clean tin vessels are to be provided - tin buckets or wash-boilers will answer very well. Also two dip-nets must be obtained, the one with a handle about seven feet in length, the other a smaller hand" net. The storage ponds are then prepared for their final purpose, and when this is all correctly done, the movable sections at the outlet of the pond containing the fish are removed one at a time. When the water is sufficiently low, the fish are carefully taken out and at once put into the tin vessels, which have previously been partly filled with clear water, assorting the fish according to size, color, etc., at the same time. When this is completed, the fish are put into their respective quarters in the storage pond with as little delay as possible. It is also at this time that the breeder makes his selection of those fish he wishes to breed from; these ought at once to be put into the winter pond.
During this fishing process it is impossible to avoid making the water muddy, so, to prevent the weakening of the fish, the supply drain is opened, allowing a constant stream of fresh water to flow through the pond.
Again the writer admonishes caution; do the work gently and neatly, as every broken fin or lost scale reduces the value of the fish so injured.
When in their respective ponds, it is not necessary to feed the goldfish, as nature provides them with all the food required for their proper growth and nourishment; but when removed to the storage ponds, additional food in small quantities may be given to them. This may consist of stale (but not moldy) white bread, dried in an oven or the open air, and crushed to resemble fine hominy or corn meal. Either of these, or both, in small quantities is strewn on the water; the fish being unaccustomed to it will eat but little at first, neither will they snap at it immediately. Gradually, however, they take kindly to it, and the quantity may be increased, keeping pace with the appetite they evince for it, giving it to them at a regular hour each day.
This feeding is not intended for the purpose of making them grow, but rather to prepare them for the change of diet that will ensue when transferred to their future homes.
When the fish take such food and thrive upon it, they may be considered domesticated, and can be disposed of as pets, they then being in condition to take readily to the more confined life in an aquarium.
When performing work of any kind on or near the ponds, or other receptacle where fish are kept, or in feeding or handling them, a patient and gentle manner is advisable, as it tends to tame the fish by giving them confidence. On the other hand, if they are frequently scared, they become of a wild, restless nature, and will dart away on the slightest provocation.