Nematodes are known to feed on plants, bacteria, fungi but many nematode species are known as parasites of men and animals. Usually those parasites are centimeters long but one of the smaller parasites is Camallanus cotti with a length of 15 mm. Camallanus cotti is an intestinal parasite of tropical fish and frequently occurs in aquaria. Related species can be found in temperate and tropical fish world-wide. The anterior end of the worm contains a rasping organ that is used to drill into the intestinal wall and provide anchorage for the worm; they feed with the blood of the fish. These worms can frequently be seen with their posterior 2 mm dangling from the anus of the fish. The picture shows the anterior end of a specimen, collected from aquarium fish.