Fish are not an essential part of a water garden; but most people decide to have them. As with plants, it is best to under-stock rather than over-stock. As a guide, to allow for growth no more than 3-in. (75 mm) length of fish should be added for every square foot of surface area.
Ideally, you should let a few weeks elapse so the plants have a chance to settle down before you put the fish in. You do not need to stick to the common goldfish these days as most aquatic centres have a wide range of other types but, before buying any, you should research the subject.
When you buy your fish, you will usually be given them in a polythene bag partly inflated with air. When you get them back to the pond, you should submerge them, still in the bag, for about an hour (not too long or they will run out of air) to let them become used to the different water temperature gradually, then they can be released gently under water – that will probably be the last you see of them for several days while they recover from their traumatic experience!
You may get casualties, either at the beginning, or from time to time in the established pool, as fish suffer from pests and diseases just as all other living things do. If you see a sick or dead fish, remove it immediately from the pool – a poorly fish must be isolated and can be treated with one of the potions that fish specialists will sell you for whatever condition it is they think yours has got, but it will probably die anyway – they have this unhappy knack — so you may find it less heart-breaking to practise euthanasia by killing it by dashing it hard on to a firm surface — it will be an instant happy release in most cases. Do not flush it down the loo, as I have often heard is done — choking them to death in sewage is not the answer.
feeding. Once the pond is established, there is really no need to offer ‘artificial’ food as in a short while larvae of certain insects will appear in the water and these provide natural nourishment, but if you must, you can give a little supplementary food once a day during summer. In winter feeding should be discontinued altogether.
These are the scavengers of the pool. They can often be introduced as eggs on new plants, though they are generally offered for sale where fish are sold. They are not considered as useful as once thought, as they can damage the plants.
Frogs and newts
These may be temporary summer visitors for breeding purposes. They usually do no harm — in fact, they eat many small garden pests like slugs and the tadpoles eat green algae in the water. Occasionally, they can damage a fish by mistaking it for another frog during the mating season.