Disease Symptoms

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This page lists the various symptoms that a fish may have and which gives clues to what may be causing the problem.

  • Fish scratching themselves against objects. - Parasite.
  • Fish keeping apart from others of its kind. - Stress
  • Fish appear extra sensitive to noise or extra shy. - Stress
  • Fish not eating or very little. - Stress
  • Fish has split or ragged fins. - Finrot
  • Fish has extra mucus coming from its gills. - Parasite
  • Fish has a gill clamped to its side. - Parasite
  • Fish has red or white lesions or lines on its body or fins. - Nitrite poisoning
  • Fish has swollen abdomen on both sides. - Bloat, Swim Bladder
  • Fish has tiny white spots over the body and fins. - White Spot
  • Fish has fuzzy white or or grey 'cotton-wool' patches on the mouth, skin or fins. - Cotton wool disease
  • Fish has a white patch or growth on the mouth or fins. - Lymphocystis
  • Fish rubbing its mouth up and down against the tank wall. - Stress


The fish has something in its gills or that part of the body. This can be caused by Ammonia, Nitrite or Nitrate levels in the water. This can be caused by Gill or Skin flukes. Could be early signs of White Spot. Parasites can also be on the surface of the fish such as with water fleas, anchorworm, and sea lice. They could be cause by neglected water or a new fish being introduced into the tank.

Swim Bladder Disease[edit]

(SBD) The swim bladder is present in most fish, and is used to keep the fish upright when swimming, and helps them go up and down in the water. Problems can be caused with the swim bladder by over feeding, constipation or an internal infection. Fancy Goldfish and Fancy Betta splendens are prone to this. Symptoms are often teamed with bloating of the stomach area.

The best way to treat a swim bladder problem is to catch it early, if you notice your fish unable to right itself, starve it for one day. Don't worry, fish can go for a surprising length of time without eating. On day 2 feed him with a little cooked de-shelled pea. This acts as a fish laxative. Starve for another day or two. Watch for any improvement.

If you notice any other symptoms it may be more than over-feeding and be an internal parasite or infection. Other symptoms that would hint at this would be a sunken stomach, not eating and hiding in the tank. In this case you will need to isolate the fish and try and treat with Anti-Internal Bacteria medications. But if the fish has gotten that far along it may be too late. Internal infections are notoriously hard to treat in fish.

Bacteria infection[edit]

See Bacteria.

Fungus infection[edit]

It often shows itself as a white cottony growth on fins and should be treated as soon as spotted to minimize fin damage. Bettas are particularly prone to fungal infections and adding Aquarisol to their water every other week is worthy of consideration if they are kept in a bowl or other small tank.


Providing an environment that is noisy, sparse or ever changing (ie reflections, moving ornaments, etc.) will alarm the animal and raise its metabolic rate so that it gets a reduced immune system and therefore more prone to catching diseases. Alway provide a cave or hiding place so that the animal can feel safe and hiden. This will calm the animal and paradoxically will allow the animal to venture out into the open more.

  • Consider hanging a dark background onto the back of the tank or placing dark substrate in the tank.

Virus infection[edit]

There are no cures for virus infections. The best you can do is try to reduce the animals stress or improve its environment so its own immune system can cope with it.

  • Offering alternative nutrition can help.

Water Quality Low[edit]

Allowing the levels of ammonia, nitrite or even nitrate to rise beyond their usual low limits will cause damage to the aquatic animal. Reduce these levels by performing regular water changes to get the levels down and examine why they were high in the first place and correct them so they don't happen again.

If the KH of the tank is low (say less than 2°d) then this can cause pH shifts throughout the day or night causing the animals to suffer serious osmotic stress and it can be fatal.

  • Also looking to the possibility of heavy metals being present in the water and try to keep the level of suspended particles low.


The most important thing to do to reduce bullying is to ensure that you have compatible tank mates and your fish are being kept according to species guidelines. For example, two male bettas cannot be tank-mates no matter how big the tank. There should be one hide or leafy plant per fish in aggressive or semi-aggressive tanks. There should also be enough room for each fish to claim their own territory.

Semi-aggressive and aggressive fish should not be kept in anything smaller than a 76 Litres (20 US G.) unless it is just a single small fish. Bullied fish will often have fins shredded or scales missing. They should be removed and watched for bacterial or fungal infections. If you don't have an extra tank a temporary divider should work. In fish that establish hierarchies some fighting will occur whenever a new fish is added. The decorations should be rearranged and at least one added to give the new fish some place to seek refuge and leave everybody to re-establish new territories instead of defending old ones.

  • Note some fish like Tiger Barbs practise status position in their shoal by using their mouths and body orientation to dominate another of the same species without doing harm. However if kept in groups of less than 4 or 5 the Barb will out of frustration try to dominate other species which may lead to harm as the other fish doesn't respond by performing a submission role and is therefore repeatedly 'attacked' or nipped.


See Dropsy.

Poor nutrition[edit]

Giving the animal the same food day in, day out will always lead to problems. It suppresses the immune system and allows the animal to pick up infections. No one food contains all the required protein, vitamins, amino acids, trace elements. So feed different foods. Bits of raw fish flesh like tilapia, tuna or salmon fillets are very good alternatives to simply feeding flake or pellets. Raw or frozen foods can contain parasites though. Adding conditioning salts to the tank helps to keep parasites down.

Disease Symptom Chart[edit]

Disease Symptom Chart
Disease causing organism Condition Symptoms Likely Causes Remedies
Appearance Behaviour
Bacteria: which may include Aeromonas, Pseudomonas, Flexibacter or Mycobacteriosis Fin Rot or Tail Rot Torn and tattered edges or white edged holes in fins, red streaks in the fin and tail, white edges to the fins and tail. Fish may appear lethargic and tired. Bacteria often infect fish when they becomes stressed, or when their immune system has been compromised.

There are many causes for this including:
Poor water quality.
Physical damage.
Previously unwell.
Introduction of non-quarantined new fish to the tank - harmful bacteria has been transferred to the tank.

Bacteria:usually Flavobacterium columnare (Flexibacter) Mouth Rot Rotting/erosion of the mouth areas. Small grey or white marks on the head, fins, gills and mouth that grow to resemble white 'fungus like' tuff, loss of colour Fish may appear lethargic, They may have clamped fins. Loss of appetite Treatment
Bacteria: which may include Aeromonas, Pseudomonas and Flexibacter Gill Rot Inflamed gills with rotting white patches Fish may appear lethargic and tired, have clamped fins, lose of appetite.
Fish may struggle to breathe (check your waters nitrite levels) and appear to be gasping at the water surface.
Bacteria:Vibriosis Ulcers or red streaks Red areas or open wounds or sores on the body that have been infected Fish may appear lethargic and tired, have clamped fins, lose of appetite. Poor water quality.
Physical damage.
Bacteria:Mycobacteriosis Fish TB Thin appearance, bloated areas in gut area of body, crocked spine, loss of colour, ulcers.
Reproduction stops in females. Guppies and other live-bearers often strongly affected
Very similar symptoms to other bacterial infections above.
Fish often appear lethargic and tired, hide in corners near the bottom. Incurable mostly.
Euthanise animal. This very hardy bacteria lives in the gut and internal organs of the animal so rapidly infects others in the tank. Long term quarantine of several months needed to ensure you don't import it.
Parasites White Spot (Ich) Tiny white spots on the skin and fins, extra skin mucus. Fish may appear irritated and flick against objects;they may look uncomfortable; loss of appetite Parasites often infect fish when their immune system has been compromised.
There are many causes including:
Poor water quality,
Poor food variety,
Adding infected fish,
Over crowding.
Parasites Costia (Ichthyobodo) Cloudiness of the skin caused by excess mucus Fish may appear irritated and flick against objects;they may look uncomfortable; loss of appetite;lethargy;clamped fins, fish may rest on the bottom for long periods. Treatment
Parasites Trichodina Grey patches on skin if highly infected Rubbing against objects, clamped fins, lethargy. Fish may rest on the bottom for long periods if seriously infected. Treatment
Fungus Often Saprolegnia Grey white patches on skin or gills that resemble tuffs of cotton wool Fish may appear lethargic and show a loss of appetite. Poor Water quality.
Fungus is a secondary infection that attacks fish on open wounds from other fish or other injuries, such as ulcers.