A NSW Government website

Caring for your pet fish

If you are a fish owner or hobbyist, you should make sure your aquarium and its residents remain happy and healthy. Here are a few things you should remember:

  • Know your fish – Some need special conditions and diet, while others are aggressive and unsuitable for a community tank.
  • Design fishponds so that plants, snails, fish, or eggs can’t escape during heavy rains, and screen all overflow areas.
  • Change the water – Replace about a third of the water in your aquarium at least once a month. Tap water may contain chemicals that harm your fish so make sure you use appropriately treated or aged water, such as using a water conditioner available from your pet shop.
  • Take care cleaning tanks or ponds - Tip wastewater on the garden; place solid waste like plants or gravel in the bin or bury them. Water, rocks and gravel from your aquarium or pond may contain fish and snail eggs, larvae, plant fragments, or diseases.
  • Remove sick fish – Diseased fish can contaminate others so remove them quickly (and dispose in general waste).
  • Don't overfeed – Feed only as much as your fish will eat in one minute and just once a day, or as advised by your pet shop.
  • Don't overcrowd – Overcrowding increases pollution and aggression problems.
  • Watch the sun - Too much sunlight on your tank encourages algae growth.
  • Quarantine live food prior to introducing it to your aquarium or pond, to ensure that any diseases or parasites are not spread to your fish!

Diseases of ornamental fish

Commonly experienced problems in aquaria include "ich" or white spot disease, a skin infection caused by the protozoan parasite Ichthyophthirius multifiliis, which manifests as small white spots over the body and fins; ‘fin rot’, where fishes' fins turn whitish and die back, often following damage or injury, which is caused by bacterial or fungal infection; and various internal or external parasites.

The names commonly given to disease problems encountered by fish hobbyists, such as ‘dropsy’, ‘pop-eye’, ‘fin rot’ and so on, are mostly descriptions of symptoms rather than specific diseases. They may be caused by a wide range of disease agents, most of which are poorly understood. Although some diseases, such as white spot disease, can cause grossly visible signs in fish, the actual cause may not be determined without suitable training and the aid of a microscope, or other specialist diagnostic tests.

A veterinarian should be consulted for disease diagnosis, and gross signs alone should not be used to diagnose and treat suspected disease in fish.

Freshwater finfish pests

While several freshwater pest fish species have long term established populations in NSW, there's been an increase in ornamental fish species reported as established in the wild. These ornamental pest fish introductions are believed to occur through both accidental and intentional release. Some may have been released by owners that no longer want the fish but were unaware of the options available for appropriate disposal, humane destruction of fish, and environmental consequences of release.