Common fish pests include Trematodes which are flatworms or flukes and Nematodes known as roundworms. Trematodes usually focus on snails or mollusks but in some case affect fish. Gill Flukes appear on the gills of fish and often take blood from the fish. Roundworms can spread quickly accross fish. A sign of a roundworm is a fish that looses weight while eating well.

Some common Nematodes are Capillaria, Eustrongylid nematodes, and Camallanus Nematodes.

All can be treated with Clout, Levamisol, Metronidazole, or Trichlorfon.