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Common Fish Diseases

Common Fish Diseases

Common diseases that are found in aquarium fish can be caused by a wide range of issues. These may be bacterial infections, fungal infections and even parasites.

Preventing Disease

Fish, like any other pets, can become ill. Thankfully the majority of infections and diseases can be eliminated or prevented by regular careful observation, regular water testing, frequent partial water changes, appropriate living conditions (correct tank size, compatible tank mates), and excellent water quality. Ensuring your fish has the cleanest home possible is often the easiest way to keep them happy and healthy for longer!

Basics of Treatment

There are some standard steps to go through if you notice any illness or irregularities in your fish that can hopefully help to stop any illness or diseases from progressing further.

  • Check your water conditions regularly to ensure your parameters are normal and stable
  • Quarantine any sick fish where possible
  • Do small regular water changes
  • Remove the carbon from your filter
  • Treat with appropriate medication (this varies by the disease/illness)

Common Diseases You May Encounter

White Spot

This nasty parasite is a common fish disease and if left untreated will affect your whole tank and may result in multiple mortalities.

The first visible sign will be small white spots on the fish – as if they have been sprinkled with salt. In the early stages a fish may be seen to rub up against objects as the irritation sets in. Other symptoms may include rapid gill movement, lethargy and settling on the bottom of the tank.

Fin/Tail Rot

This is literally the rotting of a fish’s fins or tail. frayed, and or translucent, often with white edging on the fins. There is often an accompanying loss of appetite and the fish may even settle on the bottom of the tank.

Fin rot can often come on as a secondary infection when a fish is under stress or been nipped/caught their fins on ornaments. This can be initiated by bullying and fin nipping by other fish, but again mostly caused by poor water quality.


Columinaris is a highly contagious bacterial disease causes by gram negative bacteria. It is important to catch and treat it early, as it is often fatal and spreads quickly. This is often confused with a fungal infection because of the appearance of white or grayish white spots on the head.

However this normally starts as a paler area around the head and mouth that lack the normal shiny appearance. These may become yellow/brownish in colour and be tinged red at the edges.

The mouth is normally attacked by this bacteria, although lesions can appear on the back extending down both sides of the body giving the appearance of a saddle.


Dropsy in fish is characterised by a swelling of the abdomen. It often causes the fish scales to stick out and gives the fish a “pine cone” like appearance. They also appear listless and have a loss of appetite.

There are several causes of Dropsy but it is frequently caused by a bacterial infection and it is not usually treatable. Dropsy is also considered a symptom which can be indicative of other issues that your fish might be experiencing.

Swim Bladder Disorder

The swim bladder of a fish is responsible for maintaining buoyancy. The cause of Swim Bladder Disorder is mainly mechanical such as constipation or air gulping at the surface when feeding. It can also be caused by an underlying bacterial or sometimes a fungal infection. It can also be a kidney or liver disorder, and the underlying cause will need to be treated.

This disorder mainly affects those fish with a globoid body shape: such as your fancy goldfish; Orandas and Fantails.


Contact Us

Melbourne Tropical Fish

Factory 2/41-43 Sinclair Rd

Dandenong VIC 3175

(03) 9792 5513


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