Fish are gregarious by nature, so always keep more than one, but do not overcrowd the tank and do not keep incompatible fish together. Some species are carnivorous and may attack, or even eat, the other fish. Contact your local Aquarium Society for advice.
People keeping fish for the first time would be well advised to begin with inexpensive coldwater fish, such as a few hardy goldfish, as they are easier for the novice to care for. A tropical aquarium should be set up only after having experience and success with the maintenance of a coldwater aquarium.
Never keep fish in a round glass bowl, as the mouth of these bowls is comparatively small and only a limited water surface is in contact with the air. This can result in lack of oxygen and dead fish.
An aquarium about 60 x 30 x 30 cm will take about 10 small fish and two water snails. A good rule of thumb is to allow 30 cm² of surface area to every 2 cm of fish, including the tail. An average fish will need 5 litres of water for each centimetre of body length. The fish capacity of the tank will be increased if it is artificially aerated.
Fresh water should be added to the tank when needed, to make up for evaporation. If water in the tank becomes obviously discoloured, it should be changed.
The use of a glass syphon tube and hose will facilitate cleaning. Syphon out about 1/3rd of the water. Get the tube right down into the gravel, work it across the bottom of the tank, and allow the water to run into a bucket. Never undertake a complete water change. Replace with clean, fresh water that has been allowed to stand at room temperature for 24 hours so the chlorine has evaporated. (Better still, collect rainwater and use this).
Do not overfeed your fish as this can kill them, and uneaten food decomposes in the tank. Feed lightly once a day using special food available from pet shops or supermarkets. Occasionally, give a chopped earthworm to prevent constipation.
Overcrowding and polluted water are the principle causes of death in aquarium fish. It is important that the tank is cleaned regularly to remove excreta and excess food, which will foul the water.
Gasping is a sure indication of a fouled tank. Other signs of infection and disease are - fluffy white patches or spots, a general mouldy look with loss of colouration, a rotting tail. These diseases can be fatal, so seek professional advice should they occur. Fish can also get worms and should be treated annually.
There are other ways to keep non-tropical fish and you may prefer to consider them.
Adequate aquatic plants must be placed in the pond to help oxygenate the water and to provide a shade and shelter for the fish, as well as a place for fish to lay their eggs. Rocks also provide good shelter for fish and are decorative. A water filter system is necessary to remove algae and other impurities.
The ordinary goldfish can live for up to 25 years in a natural pond environment, but their lifespan is much shorter when they live in an aquarium.