Many gardeners like the idea of having fish in their ponds to create an added element of interest and perhaps to bring an air of tranquillity to the garden. However, adding fish will also add to the amount of maintenance that the pool will need; you will need to ensure that the water contains enough oxygen and you may have to spend time replacing plants that have become damaged by the fish.

Oxygen

Oxygen levels can be kept to an acceptable level by using plenty of oxygenating plants. However, you may find that in hot weather that the fish become listless and come to the surface of the water gasping, indicating that the oxygen levels are not high enough. You can remedy this by installing a pump and fountain; moving water will increase oxygen levels. Alternatively, gently spray the water surface with a hosepipe.

How Many Fish?

The general rule when stocking a fish pond is that you can have 2 inches of fish for every square foot of surface area. This body length measurement of the fish does not include the tail.

This means that a pond that is 6x4 ft (24 sq ft) can support 48 inches of fish; for example, 8 goldfish that are 6 inches long.

Overstocking the pond will often result in it becoming cloudy as algae will feed on the excess waste.

What Sort of Fish?

Goldfish

Despite their name, goldfish are available in a whole range of colours, from white to many shades of orange and combinations of both. They are easy to look after and hardy, growing to a maximum of about 15 cm (6 in).

Golden Orfe

Orfe are longer and thinner than goldfish and tend to swim much faster. They are usually a very pale gold colour. As they are slightly bigger than goldfish, they will require a little more room. As well as being decorative, golden orfe eat duckweed and will also feed on any insect larvae present.

Koi Carp

Koi carp need a larger and deeper pond than goldfish (at least 1 m or 3ft deep) and much more care. They are available in a range of colours and can grow in excess of 30 cm (12 in). Although young fish may be fairly reasonably priced, mature specimens can be extremely expensive, with enthusiasts paying thousands of pounds for them.

Tench

Tench are a native species sometimes used as pond fish, but as they are bottom feeders, they often stir up the mud at the bottom of the pond making the water cloudy. Consequently, they are only really of use in wildlife ponds, where they are much less damaging to tadpole populations than non-native species.

Adding Fish to a Pond

Fish are best added to a pool in the summer months when the water is warmer, as they become semi-dormant in cool weather and may be much more prone to stress. Do not introduce them for at least a month after planting up, so that the plants (especially the oxygenators) have a chance to establish themselves.

If you are adding a number of fish, it may be better to do this in two stages, 2-3 months apart. This will allow the bacteria levels in the water to become sufficiently high to deal with the increase in fish waste products.

Fish are very sensitive to temperature changes, so you should never release them straight into the pond. Instead, float the bag that they are supplied in unopened on the pool surface until the water temperature inside the bag is the same as in the pool; this should take about an hour. You may need to shade the bag in very sunny weather. Gradually add small amounts of pond water into the bag before finally releasing the fish by gently opening the bag and letting the fish swim out on their own.

Other Aquatic Creatures

It can be a good idea to introduce a number of other water creatures to help keep the pond clean. Mussels, especially the swan mussel, are particularly good scavengers. Ramshorn snails are also useful, but avoid ordinary pond snails as they tend to eat water lily leaves.