White Grunt with an Isopod Parasite Attached to it in Cozumel

White Grunt with an Isopod Parasite Attached to it in Cozumel, Mexico

White Grunt (Haemulon plumierii) with a Cymothoid Isopod Attached

White Grunt (Haemulon plumierii) with a Cymothoid Isopod Attached

What is that “thing” attached to that fish?

This white grunt, Haemulon plumierii, has an isopod permanently attached to it below his eye and above his mouth. I found this one while diving on Colombia Shallows, a spectacular dive site, today. The grunt definitely appeared anemic and was showing the effects that its parasite partner is causing. We don’t see many isopods on fish in Cozumel but they aren’t necessarily rare here either.

The cymothoid isopod is a parasitic crustacean belonging to the same group of marine creatures as the lobsters, shrimp, barnacles and crabs. As an ectoparasite, Isopods are ectoparasites meaning that they live on the outside of the host, either on the skin, on fins, in the gills or other body parts of its host fish. They can cause serious tissue damage, slowing development, lethargy due to a loss of blood and eventually the death of its host fish.

Most species of isopods feed only on blood and need a specific host species on which to feed, in the case of this photo – a white grunt, in order to survive. It’s also fairly interesting to know that isopods are also very particular about where they attach themselves to their hosts.

Strange fact: Some types of isopods are called “tongue biters” will actually crawl inside of a snapper’s mouth, sever the fish’s tongue and live in the host’s mouth for the rest of its life. The isopod replaces the fish’s tongue and feeds on scraps of food left in the host’s mouth.

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