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Note for Pet Owners

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

One of the common signs of disease in fish is the appearance of spots on the surface of the skin - but what causes them ?

Spots or patches frequently appear on the surface of fish and they can either lie within or below the scales, or form a swelling which protrudes above the surface of the body.

Spots come in different colors which can be helpful in identifying an underlying cause :

Color of spots Possible causes
White Fish pox; Cryptocaryon; Ichthyosporidium ; Ich (white spot); Nodular disease; normal to get white spots on the pectoral fins and gill plates of male goldfish during breeding time.
Yellow Black spot, Yellow grub 
Black Black spot, Yellow grub 
Red Fish pox; Lymphocystis; Inflammation
Brown Black spot
Grey Cryptocaryon; Ichthyosporidium

Black Spot

Small black or brown spots upto 2mm in size on the body or fins. Caused by a worm. It affects coldwater fish including Goldfish, Carp, Tench and other Cyprinids. 

Cryptocaryon (also called "salt water ich")

Caused by a marine parasite. Causes grey-white nodules about 2mm in size. It irritates so fish rub themselves against objects. 

Fish pox (also called carp pox or skin papilloma)

This is caused by a virus and it forms small white spots which are opalescent. These merge causing large patches and later they turn reddish-grey.  It mainly affects carp.

Ich (white spot)

Caused by a parasite (Ichthyophthirius) - look like small pinhead spots on the fins and body. This disease affects all freshwater aquarium fish. Fish rub themselves against objects. 


Small white nodules appear on the skin. Fish often have a swollen abdomen as well. It is caused by a fungal infection .


Reddening of the skin all over the body is associated with bacterial septicemia. Fish can become very ill and die rapidly. 

Lymphocystis (also called cauliflower or raspberry disease)

Small white nodules occur on the skin and fins and grow to 2mm size tumours. It is caused by a virus. Fish often die from this.

Nodular disease

Sporozoan infections cause cysts (containing the parasite) varying in size from pin-head to pea-size spots. They affect a wide variety of fish. Some affect the balance of fish they infect.

Yellow Grub

Similar to black spot. Causes black or yellow spots in tropical fish. Caused by Clinostomum sp.


Some of these conditions can be treated relatively easily - others cannot. Some of the diseases can survive in the aquarium and re-infect fish later. Some present a serious risk to other fish. So, if you have a fish showing these signs get the advice of your veterinarian as soon as possible. 




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