Goldfish are such a successful and indeed popular fish for the garden pond because they are so tolerant of a range of pond conditions.
The goldfish is the golden variety of a lowland freshwater carp species whose biology and lifestyle is adapted to slow and still waters.
Such waters will also carry significant levels of minerals and other matter that have washed into the valley through the entire course of the river. It is not surprising therefore that goldfish have been known to live in the meagre conditions afforded by a goldfish bowl.
Although this can give us confidence in our abilities to satisfy the goldfish’s requirements in a garden pond, it by no means should make us blas about keeping them.
Goldfish have specific environmental requirements, and if they are provided, will stimulate them to grow and probably even breed.
Goldfish are tolerant of a massive temperature range from ‘freezing’ to waters above 30oC. They will not be active or generally feed below 8oC. They will feed and grow above this temperature and breed at about 16oC and above. Goldfish will not tolerate rapid changes in temperature and care must be taken when carrying out water changes so as not to unduly stress its inhabitants
Goldfish have a low dissolved oxygen (D.O) requirement compared with some other pondfish. They will gasp at the surface when D.O. drops too low. This is more likely to happen in warmer temperatures when water will hold less D.O. or if the water becomes polluted through overfeeding or after an algicide or other medication has been used.
A healthy D.O. can be maintained by aerating the pond with an air pump and airstone or more simply through a fountain or waterfall.
Fish are constantly excreting toxic waste, which can be a real problem in warmer temperatures when they are actively feeding. A biological filter must be installed if a pond is stocked in excess of natural stocking rates. This will breakdown the toxic ammonia produced by fish into less harmful nitrates, which can be utilised by plants.
Although not an essential requirement for keeping goldfish healthy, plants in a garden pond can perform a number of useful and beneficial roles.
Grazing/Browsing. Goldfish will browse and use some softer submerged weeds as a supplement to their diet.
Oxygenation Submerged aquatic weed will add beneficial oxygen during the day. The tougher Hornwort will not be eaten by goldfish, whereas they will happily graze on Elodea crispa or E. densa.
Spawning Material Submerged aquatic plants provide an excellent spawning material for goldfish. Goldfish release many thousands of tiny adhesive eggs which will stick to submerged weed, and hatch under the protection of this dense vegetation.
The pH can be tested quite easily using a test kit, which are available from aquatic stores. It should be between 7 and 9 and under no circumstances should it drop below 7 to become acidic.
Healthy goldfish will exhibit normal behaviour which will include them actively feeding and swimming. They are gregarious, so any ‘loner’ goldfish are showing atypical behaviour and are likely to be unwell. A simple visual health-check can be carried out by observing the fins of the goldfish. If they are all erect and well displayed, then this is a sign of good heath. If they are clamped, especially the dorsal, then it is likely to be unhealthy.
Goldfish will feed from March through to October, when the water temperature is above 8oC. They will benefit from a floating pellet or stick which enables goldfish to be viewed and inspected at feeding time. Smaller goldfish can be offered flake. They should be fed what they will eat in 5 minutes, being fed several times a day. Look out for foods that offer colour-enhancing properties, improving the colours of goldfish and other pondfish. A quality colour enhancing diet can turn your goldfish into a deeper red!