Aquarium Fish Tank

Fish Diseases

Fish Diseases and Common Fish Illnesses

So lets get started...in alphabetical order we will start with Anchor Worms.

Anchor Worms

  • Scratching - clearly your fish will want to remove the worm by rubbing against the tank walls, any objects in the tank will also do

  • Whitish-green threads hanging from the fish's skin

  • Points where attached will be marked by inflammation

Anchor Worm on Fish



Infected fish.  The young anchor worms (Lernaea parasite) burrow into the fish’s skin and enter the muscles. Here they begin to develop and release eggs before they die—leaving behind damage, which can become infected.



Common methods include physically removing the parasite and cleaning the wound with an antiseptic like iodine. Also common is bathing freshwater fish in a seawater bath (35ppt) for about 5 minutes for multiple days until the parasite falls off. You can use a medicated bath to prevent secondary infection. Insecticide may also help.





Body flukes

(flatworms approximately 1 mm long)

  • Scratching - clearly your fish will want to remove the worm by rubbing against the tank walls, any objects in the tank will also do

  • Layer of mucus covering gills or body

  • Gills moving rapidly

  • Chewed on or eaten-away gills or fins.

  • Reddened skin

Body Flukes



Poor water quality, overcrowding and/or stress by caused by other species—creates conditions that can lead to destructive outbreaks. Flukes are often present in aquariums but remain harmless under ideal conditions. Avoiding stressful conditions is a key to prevention, but once an outbreak occurs, prompt treatment is critical.


Anti-Parasitic Fish Medication – Such as Tetra Parasite Guard® with praziquantel is effective but must be carefully administered per directions. Alternatively, a wormer that includes flubendazole for fish with parasites and flukes works well too.  Flubendazole works differently to other Fluke treatments by gently starving the parasite; making this product perfectly safe for regular usage.

Secondary infections are also common and can be treated with antibiotics or general cures like Lifeguard® or Fungus Guard®.

Note: Pale fish with drooping fins, rapid respiration and/or hollow bellies indicate more extensive infestation.


Water treatments can be reviewed HERE.



Further Reading

We suggest for updated information a great source is Wikipedia: List of aquarium diseases

Disease Cause Fish Affected Symptoms Treatment
Anchor Worm Lernaea parasite All Visible parasites attached to body leading to ulceration and irritation Remove parasites with forceps and use medicated bath to prevent secondary infection. Insecticide may help
Dropsy Varies from temperature, to indigestion to infection All Bloat, scales stick out Varies depending on the cause
Egg Fungus Fungal Eggs only Fungal growths on eggs Remove affected eggs. Use Methylene blue to medicate the hatching tank.
Fin Rot Bacterial All Erosion at edges of fins Improve water quality, remove fin-nippers and feed Vitamin C - enriched food. Use anti-fungal treatment to prevent secondary infections
Hole-in-the-head Hexamita parasite Discus and Cichlids Pale ulcerated area around head Metronidazole or similar medication. Use food containing Vitamin C
Iridovirus Viral Gouramis, angelfish, Ramirez Dwarf Cichlids and others loss of appetite. Darkening in color. Enlarged abdomen. Occasionally Lymphocystis None
Lymphocystis Viral All Cauliflower-like growths and white areas around the eyes Vaccines may be available
Malawi Bloat Probably viral Lake Malawi Cichlids, especially vegetarian ones Similar to Dropsy Offer a high-fiber diet
Mouth Fungus or Columnaris Flexibacter 
All, especially Livebearers Cottony growth near jaws and loss of appetite. Improve water conditions. Use commercially available antibiotics
Neon Tetra Disease Pleistophora hyphessobryconis 
Neon Tetras Discoloration None
Piscine Tuberculosis Mycobacterium marinum bacteria All Weight loss evident on underparts, with corresponding loss of appetite, papules, discoloration and bulging eyes. Amputation
Pseudomoniasis Pseudomonas 
All Hemorrhages in mouth and ulceration on body Medicated food
Saprolegnia Fungus Fungal All Whitish, fur-like growths Vitamin C enriched food, or a commercial remedy in a medical bath. Check to make sure that your fish doesn't prefer Brackish water
Septicemia or Egtved virus

Piscine novirhabdovirus 

(originally called Viral hemorrhagic septicemia (VHS) virus)

Many fresh and salt water fish

Hemorrhaging, internal and external.  Bulging eyes, bloated abdomens, bruised-looking reddish tints to the eyes. 

May appear listless or limp, hang just beneath the surface, or swim very abnormally, such as constant flashing circling.

Virkon AQUATIC to clean the tank and everything in it to remove it.   

There is no specific treatment or cure for VHS. 

Fish with VHS will die.

Skin or Gill Flukes Gyrodactylus and 
Dactylogyrus parasites
All Labored breathing, scraping against objects, abnormal gill function Commercially available medication
Swim Bladder Disease May be bacterial, or caused by chilling or digestive issues All, especially Balloon Mollies Inability to balance in the water Check water temperature. A medical bath may help.
Velvet Disease Oodinium and other parasites All salt and freshwater fish Brown to gold to green 'dashing' dots, rubbing against rocks while swimming, sporadically dart from one end of an aquarium to another Sodium chloride (table/sea salt), copper sulfate, methylene blue, formalin, malachite green and acriflavin
Vibrosis Vibro bacteria All Discoloration, reddish staining of fins, bulging eyes, lethargic behavior Medicated food
White Spots (Ick) Ichthyophthirius multifiliis parasite All Small white spots, which may ulcerate Raise water temperature slightly and treat water with commercially available remedies