Fish Parasite Identification Guide (16 Easy Steps)

Identifying fish parasites can be a difficult task without the right guidance and resources.

The underwater world of fish is full of complex and interesting creatures. It is important for people who keep fish as pets, or who work in the fishing industry to be aware of the different parasites that can infect them.

This article provides an fish parasite identification guide with 16 easiest steps to identifying common fish parasitic groups.

Fish parasite identification guide

How To Properly Identify A Fish’s Parasites?

Properly identifying fish parasites can be a bit tricky, as many different types of parasites can infect fish and they can present in a variety of ways.

However, there are 16 steps you can follow to help identify fish parasites:

StepsGuidelineYES/ NOFollow
1.Organism microscopic 2
 Organisms not microscopic, visible in naked eye 4
2Body one celled, or a part of group of similar cells Protozoa
 Body multicellular 3
3Organism worm like, equipped with hooks and hooklets at posterior end of body; external parasites Monogenea
4Organism encysted on external surface of host 5
 Organism not encysted on external surface of host 7
5.Cyst containing one organism 6
 Cyst containing thousands of organisms Protozoa
6.Organism one-called (Ichthyophthirius) Protozoa
 Organism multicellular Digenea
7.Body more or less flattened 8
 Body not flat 13
8.Body segmented 9
 Body un-segmented 10
9.Organism with anterior and posterior suckers, digestive tract present, external parasite only (may occur in mount) Hirudinea
 Organism with single anterior hold fast which may have several suckers, digestive tract absent, intestinal parasites Cestoda
10.Organisms with mouth and gut cavity, no anus, well developed organs of attachment 11
 Organism without mount or gut cavities, poorly developed suckers at anterior end 12
11.Organism equipped with hooks and hooklets at posterior holdfast Monogenea
 Organism lacking posterior hooks, equipped with oral and ventral suckers Digenea
12.Internal organs present, visible with aid of reflected light (Caryophyllidae) Cestoda
 Internal organ absent (larval form) Cestoda
13.Body cylindrical 14
 Body not cylindrical 16
14.Body plastic, organism active; movements eel-like Nematoda
 Body not plastic, form fairly rigid 15
15.Intestinal parasites, organism with numerous spines on proboscis at anterior end Acanthocephala
 External parasites, organism with antler-like protuberances at anterior end (Lernaea) Copepoda
16.Body leaf-like; resembling fish scale (Argulus) Copepoda
 Body viable, with obvious appendages for attachment to gills of host Copepoda


  • A practical textbook of fish parasitology and health management. 2008. By Kirtunia Juran Chandra. UGC.