The Goldfish
Kept by man for many, many years, Carassius auratus (the Goldfish) is probably the best known of all aquarium/pond fishes. The wild form of this fish is a dull green to brown animal with little to recommend it as a potential aquarium fish, but a mutation occurred which developed lovely gold patches on the body which eventually turned the whole fish gold. The goldfish had been born. Its first recorded breeding in Europe took place in Holland in 1728. In its native China it has been domesticated even longer (since around 800 AD), and many fancy strains have been developed. The standard goldfish is the ideal pond fish, developed from the wild green/grey specimens into the reds and golds we see today
Man has developed a multitude of variants with both single and double tails and various colours. Generally speaking, the singletailed types, including the common goldfish, comets, and shubunkins, are excellent pond fishes. Small specimens of these types also make good hardy aquarium fishes which may live in excess of twenty years. The double-tailed varieties are much more delicate and are best kept at warmer temperatures (10-15°C/50-59°F; thus they will not overwinter in an outdoor pond) in an aquarium, where their fine body shapes and finnage forms can be better appreciated.
Goldfishes are tolerant of most water conditions but a large aquarium is required if you are to keep them well. The old-fashioned goldfish bowl is not suitable: it has limited surface area for the uptake of oxygen into the water, no room for a filtration system, and insufficient swimming space An aquarium is far better to keep a goldfish happy, and there are companies which produce a package which contains everything including the tank and filtration system -you just add fishes, plants, and water. Goldfishes are noted for being messy, greedy feeders that produce a lot of waste. Needless to say they require a very efficient filtration system to cope with this. There is a good range of goldfish foods available but don’t forget to include some vegetable matter as well as live or frozen foods in their diet.
Do not try and overcrowd your fishes as this places a great deal of stress on them. If conditions become too warm and the dissolved oxygen level falls, the fishes will gasp at the surface, their fins will become clamped to their bodies, and signs of fin congestion (bloodshot bases to the finnage) will appear. A partial water change to lower the temperature, and a check on the filtration system, will usually counteract the problem, which could, however, also be indicative that your fishes are overcrowded.
Breeding Goldfishes
Breeding goldfishes is relatively easy. In the garden pond it should occur naturally and some of the fry may survive to maturity. To breed under controlled conditions, condition your chosen pair well on live foods. When ready to spawn the male will develop tubercules on his head, operculum, and pectoral fins; the female will be noticeably rounder.
Use a 100 x 30 x 30 cm (36 x 12 x 12 in) tank with spawning mops suspended in it so that the pair can swim through them, depositing and fertilizing the eggs as they do so. Once spawning is complete the pair can be removed and the eggs left to hatch. Feed the fry copious amounts of small live foods. Allow plenty of space for growing on, and cull the numbers rather than crowding if only limited space is available. Captive breeding has resulted in some, to our way of thinking, horrendous strains being produced. Some have enlarged, bulbous eyes (celestials and bubbleeyes) and these require special care, ensuring there are no sharp objects on which the fishes can damage themselves. Yet others have been bred to enhance cancerous growths on their heads (lionheads).
The choice is yours as ton whether or not you wish to keep these types.