Crustacean Invasion

08 Feb, 2023

Parasitic copepods and isopods that sometimes attack marine aquarium fishes

By Jay F. Hemdal

Excerpted from the March/April 2023 Issue of CORAL Magazine

Two lessons: On rare occasions, some very strange predators can appear, uninvited, in the marine aquarium. And: Things are not always what they seem to be!

Some 40 years ago, I was watching a group of Purple Firefish (Nemateleotris decora) being held in a wholesale livestock facility. One fish had a yellowish tangle of “tubes” protruding from its abdomen. At the time, I had recently learned that some collectors in the Indo-Pacific were utilizing tiny harpoons to capture gobies for the aquarium trade. The idea was that, rather than using cyanide, the collector would spear the fish in a fin or other non-critical location in order to capture it. Indeed, Mandarin Dragonets would show up at wholesalers with tiny holes in their fins from being captured in this manner. Going back to the Firefish—I jumped to the presumption that this particular fish had been speared in the gut, and these were its intestines protruding out. Visually, that all made sense back then, but the reality was, as I later learned, that the “intestines” were just the egg case of a copepod parasite.


Colin, Patrick 1975 Neon Gobies.  TFH Publications, Neptune New Jersey.

Dugdale, W., Metzger, K.  2016  Health Impacts of Cymothoid Parasitic Isopods on Symphodus tinca and Boops boops Hosts in the Northwestern Mediterranean Sea.  University of California, Santa Cruz     

Grutter, A.S. and Bshary, R.I.  2003  Cleaner wrasse prefer client mucus: support for partner control mechanisms in cleaning interactions. Proc. Biol. Sci.

Hemdal, J.F. 2023 Diseases of Aquarium Animals. In-press.

Narvaez, P. Morais, R.S. Vaughan, D.B., Grutter A.S., Hutson K.S. 2022.  Cleaner fish are potential super-spreaders.  J. Exp. Biol.

Vaughan, D.B., Grutter, A.S., Hutson, K.S. 2018.  Cleaner shrimp are a sustainable option to treat parasitic disease in farmed fish. Nature

Related Posts

About the author

Avatar photo
James Lawrence

James Lawrence is editor & publisher of CORAL Magazines and Microcosm, Ltd., publishers of a number of critically acclaimed and bestselling books in the aquarium field. He is the recipient of national and international awards for journalism, design, and publishing excellence. James Lawrence lives and works in Shelburne, Vermont.

Leave a reply