Lice
The "fish louse", Argulus sp., is a crustacean parasite of many species of pond and ornamental fish. Common symptoms for fishes infected with lice include lethargy (due to anemia), paleness, and inflammation and redness surrounding the affected area. Fishes with these parasites will also rub or brush against objects, attempting to remove them on their own.
Anchor worms
Anchor worms (Lernaea spp.) are external copepod parasites that attach to fish under scales.
Symptoms include -
Frequent rubbing or "flashing"
Localised redness.
Inflammation on the body of the fish.T
iny white-green or red worms in wounds.
Breathing difficulties.
General lethargy.
Gill flukes
Gill flukes or Dactylogyrus are parasites, which particularly lodge in the gills of koi. A gill worm consequently is a very dangerous parasite, which will not become larger than 0.1 to 0.3 mm.
The symptoms of infection by gill worms include keeping one gill shut, accelerated breathing, shaking the head, swimming backwards and rubbing gills.
Leeches
Leeches are known to commonly attach to both marine and freshwater fish. They mainly affect the fish by feeding on the blood. They are also known to transmit bacteria and viruses to the host. The feeding or attachment wounds caused by leeches may also serve as sites for secondary pathogenic invaders.
Eye Fluke
Eye fluke, Diplostomum spp, causes cataract in affected fish leading to visual impairment and, ultimately, blindness resulting in affected fish becoming dark, unable to feed, losing condition and having an increased susceptibility to predation. It also causes 'acute cercarial attack' as a consequence of a massive invasion of larval parasites into the body of the fish causing amazingly severe pathology and damage.
Y Grub (Clinostomum spp.)
These worms appear as small, yellow cysts in the flesh or skin of fish. Heavy infestation makes the fish unfit for eating.
Gill Maggots
Gill maggots are the mature females of the parasitic crustacean Ergasilus.
Ergasilus (gill maggots) will appear as grayish black and white parasites several millimeters long infesting the gills. Heavy infestations can cause severe damage, eroding the gill filaments and allowing secondary infections to develop.
Monogenetic Flukes
Monogenetic flukes or Monogeneans are flatworms that are usually found as ectoparasites of fish. Fishes infested with monogeneans may become lethargic, swim near the surface, have clamped fins, seek the corners of aquaria or the sides of the pond, and have diminished appetite. They may be seen rubbing the bottom or sides (flashing) of the tank. Scale loss may occur where the monogeneans are attached, and the skin may vary in color where the parasites have fed. Heavy gill infestations result in respiratory disease. Secondary infections with bacteria and water molds are common on tissue that has been damaged by monogeneans.
Digeneal Flukes
Digenea are common parasites in fish. Migration of the cercaria causes hemorrhages, necrosis and inflammation along the migration path. In case of heavy infestation: Death of the fish may occur especially small fish. White nodules ranged from 1-4 mm in diameter found in skin, muscles or viscera or other parts of the body (called white grub). When the nodules are yellow in color, the resulting syndrome is called Yellow grub disease. When the nodules are black in color, the disease is called black spot disease.
