Breeding Goldfish. The breeding season for the goldfish is in the late spring and early summer. In New Zealand goldfish will generally spawn anytime form early September through to late February. Usually goldfish are over 8 cm long before the sex is recognizable and they will breed. Males will get “nuptial tubercles” on their head, body, and fins when in breeding condition. These tubercles appear as hard white pimples, about the size of a pinhead, and look much like the ich or other parasites. A fish bearing these tubercles is always a male. Their abdomens swollen with mature eggs the ripe females can be easily recognized by their body shape.
For best results keep males and females separated before breeding. Feed them well with a variety of foods – good quality dry food supplemented with live food. When the breeders are well conditioned and ready for breeding prepare an aquarium or pond with mesh water. The ratio we recommend is 3 males to 2 females. The fish will generally spawn with an increase in temperature of about 2ºC. You can either let this happen naturally as weather patterns change, or spawning can be induced by simply raising the temperature a little. Goldfish will breed at any temperature between 10-26ºC, although about 20ºC is the optimum. It is important to remember that it is the change in temperature not the actual temperature, which triggers spawning activity.
Since goldfish scatter sticky eggs haphazardly over the aquarium, it should be well stocked with aquarium plants. Try to arrange the aquarium with floating rooted plants, along with some bottom plants or artificial spawning grass. You can also use soft willow or ponga fronds. As long, as the material used is not abrasive and does not risk injury to the Ash. When the pair is ready to breed it will be noticed that the male will be staying quite close to the female and finally the two come together in a spawning act, at which moment the eggs are laid and the male fertilizes them. the eggs adhere to the first thing they touch as they settle. Infertile eggs are sticky too, but they turn white in a few hours and begin to decay. If possible remove all white eggs. The fertilized eggs are about 1.5 mm in diameter and are amber-coloured when first laid. Spawning is usually large, from about 500 to 2000 eggs, depending upon the size and condition of the female. The parents should be removed immediately after spawning, which usually lasts about 3 hours. Eggs should be incubated for 8 or 9 days at 18ºC. Ten drops of 1% Methylene Blue should be added to each 10 litres of well-aerated aquarium water.
Although the eggs will hatch after 2 – 5 days, the embryo needs 3 days or so to absorb all the yolk. It is important not to feed the fry until after the 3rd day and they have consumed the yolk. Once the fry have digested the yolk, they require copious amounts of live food. Feed them on a diet of newly hatched brine shrimp or JBL Nobilfluid,you can also use boiled egg yolk fed through a stocking and after a week finely powdered dry food may also be fed. Care must be taken not to overfeed fry as excess food will quickly pollute the water and kill all the young fry. Make sure you give the fry plenty of good quality food, good water quality, along with plenty of space to swim in and watch how quickly they will grow!