Each year, as the days grow longer in the springtime, mature goldfish begin the process of producing eggs in the females, and milt in the males. Many of these changes are triggered by increasing daylight and warmer water temperatures. The availability of increased food production in the form of bloodworm and gnat larvae, if the goldfish live outdoors, adds to the changes in the fish. The changes which occur in goldfish include a general swelling in the female, as eggs begin to develop, and the appearance of tiny bumps, or “tubercles,” on the leading edges of the pectoral fins, and on the gill covers in males.
In warmer climates, goldfish may begin spawning outdoors at the end of April, but in most other areas, goldfish begin spawning in May or June. In many cases, fish spawn without any apparent indications, especially if fish are kept in a pond, and in a mixed population. For Goldfish kept in aquaria, the signs are present if the fish are closely observed. Spawning will take place early in the morning, usually just before sunrise. Spawning activity seems to be triggered by several factors, including: rainfall on the days preceding spawning; a drop in water temperature of a few degrees; partial water changes; and a full or nearly-full moon.
Spawning will generally last several hours, and thousands to tens of thousands of eggs will be laid, depending on the size of the female. Eggs are generally quite small, round, and sticky. Please see the
following picture of eggs taken in an indoor aquarium, to get an idea of the size and shape. Please remove adult fish after a spawn, if you wish to raise the babies. Adult fish will eat eggs (and fry) after a spawn. Baby fish, once recognized, will not be eaten by mature goldfish. Fish generally recognize babies once they reach ½” to 1” in size.
Eggs will generally hatch in from 4 – 7 days, depending on the water temperature. The fry are quite small at the time of hatching, and feed for the first 3 -5 days on the attached yolk sac. Upon hatching, and for a period of approximately two weeks after hatching, fry will stay attached to the surface on which the eggs were laid, or near the surface of the water. As their swim bladder begins to function, the fry will begin swimming at various levels of the aquarium.
After the fry have depleted their yolk sacs, you should begin to feed them food. Early foods can include the following: newly hatched brine shrimp; boiled egg yolk; and infusorians. For folks that have an outdoor pond, feeding can supplement food that the fry will find in the pond. For people who have fish housed in an aquarium, food will have to be supplied by the owner. After a few weeks, crumbled flake foods, small fry food, crumbled freeze-dried blood worms, daphnia, and brine shrimp can be fed to the fish. During the phase of early development, feed the fish several times a day (perhaps 3 – 5 times daily) in small quantities. It is important to carefully monitor water quality and to make periodic water changes, as some foods (especially egg yolk) can foul the water.
Metallic fish will begin to de-color, that is change from the wild green color, at 2 – 3 months old. For nacreous and matte fish, colors will tend to deepen as the fish mature. More nacreous and Matte fish start out with a mottled white coloration, with reds, blacks, oranges and blues developing as the fish age. Please see the pictures below to get an indication of goldfish development as the fish mature.
If you are raising fry for GoldFish breeding or show purposes, you will need to select fry that meet characteristics which you have established in your breeding program. Fry with deformities such as missing fins, tripod tails (in the case of the double tail varieties), and other physical defects can be given away or disposed of beginning at 6 – 7 weeks. The practice of selecting fish with certain characteristics is known as “culling.” A second culling can occur at 8 – 10 weeks, and will concentrate on coloration and conformity to bred standards. A 3rd culling can be done a 3 months, at which time most fish will begin to exhibit special breed characteristics, such as head growth, eye development, and pearl scales.
It is not unusual for only 5 – 10% of a spawn to remain after the third culling. While some people object to the thought of giving away fish, or culling a spawn, goldfish will not thrive in over crowded conditions. The practice of reducing the population size is necessary for goldfish development and quality. As fish approach 2 – 3 months in age, attempt to feed a larger percentage of live, frozen, or freeze dried food. Increased protein content in the food is required for the development of head growth pearl scales in particular. Avoid feeding floating foods, which, while good for koi, and not very helpful for goldfish, particularly the fullbodied double tail fish. Continued feeding of floating food will cause the goldfish to ingest large quantities of air, and may upset the fishes’ equilibrium. Sinking pellet or granulated food can be fed at 2 -3 months as a supplement to live or frozen food.