External Fish Macro-Parasites

(Gill Mites, Aquatic Lice, Gill Flukes, Anchor Worms et. all)

Common Indicators: Issues vary by parasite, but often irritation of the skin, gills etc.

A variety of parasites are possible to infect aquarium fish that are outside the realm of dinoflagellates, protozoans, bacteria and other micro parasites. This article isn’t meant to cover them all nor be a complete reference. However, it is worth briefly surveying a few of the more common offenders.

Flukes (Monogenean Infestation) includes skin fluke, gill fluke and eye fluke. These terms cover a large range of related parasites are common, and varieties affect both freshwater and marine tropical fish in aquaria. Poor water quality in the aquarium can instigate an infestation. Polluted water both provides a rich nutrient culture for them and induces stress on the fish, reducing their resistance. Some common indicators of the disease are pale, patchy coloration on the skin and blisters. Sometimes clamping of the fins can also accompany an infestation. Behavioral signs can include lethargy and hanging on the surface.  Often, flukes can be seen with the naked eye. However, over time the fish’s skin may cover the parasites with mucus, obscuring them.  The parasites survive by eating skin fragments and sucking the blood of the fish.According to Edward J. Noga some common treatments are Praziquantel, Formalin or Copper. Different specific species, according to this text, respond differently to medications and different compounds have various efficacy.

Fish Louse, Sea Lice & Anchor Worms (Copepods) are small aquatic crustaceans. A majority are free-living, but a significant number, around 1,700 species, are parasitic. A majority of these are marine, but a significant number are freshwater parasites. Not all have been identified. Sea Lice and Fish Louse varieties both infest the skin. Anchor worms latch onto the skin, and heavy infections can result in secondary infections and disfigurement. According to Edward J. Noga, Organophosphate is often effective if applied as a bath every 7 days for28 days —although resistant strains have been identififed.

Gill Mites are a common parasite that  feed on the blood and skin particles. Common indicators are the gills being distended and red. Behavioral indicators are lethargy and gasping for breath and hanging near the water surface. The best course for gill mites is prevention: including proper quarantine and inspection of fish to be introduced. I has been suggested that a combination of sterazin and octozin with the treatment repeated in five days to kill new hatchlings.


Bibliography & Further Reading:

Noga, Edward J. “Fish Disease Diagnosis and Treatment.” 2nd Ed. John Wiley & Sons; 2010

Stoskopf, Michael K. “Fish Medicine.” W.B. Saunders; 1993

Brown, Lydia Ed. “Aquaculture for Veterinarians.” Pergamon Press; 1993

Duijin, C. Van,. “Diseases of Fish.” Iliffe Books UK; 1973


Razouls C., de Bovée F., Kouwenberg J., Desreumaux N. “Diversity and Geographic Distribution of Marine Planktonic Copepods.” http://copepodes.obs-banyuls.fr/en; 2005

Advisory: The information contained in this article entry is for informational purposes only, and is not a substitute for consultation with a veterinary professional nor treatment under the supervision of a veterinary professional. New Life International does not guarantee the accuracy or completeness of the information nor of the sources cited as reference. This articles is not a diagnostic tool or reference, nor should be considered treatment advice by New Life International.

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