Signs Of Infection

Small black or brown spots up to 2mm diameter on the body and fins.

Fish Affected

Black Spot, Neodiplostomum cuticola, is confined to cold water species such as Goldfish , Carp and Tench. However, a similar condition, Yellow Spot (Clinostomum sp.) can affect tropical aquarium fish.

Details Of Infection

The spots are the larvae of an intestinal worm. The adult worms live in the intestines of birds that become infected by eating infested fish. Eggs are produced by the adult worms inside the bird's intestines and are passed via droppings to the water where, the eggs then hatch and become free swimming. The free swimming larvae are initially hosted by water snails where upon they are then passed on to fish. When on the fish, the larvae encases itself in a black membrane producing the visible spots. Birds will once again eat infected fish and so the cycle repeats.

Because of the life cycle of the worm, the condition is not infectious between fish.

Treatment

The simplest form of treatment is to break the life-cycle of the parasite either by ensuring that birds do not approach the fish or that no snails are present in the pond.