Featured Image: © Nico Smit via pbs.org
By: Katie Gillis
Fish in the ocean have something new to fear…. a parasitic isopod that eventually replaces their tongue.
Cymothoa exigua is a parasitic isopod that infests a host through the gills. The cycle is quite interesting, as the isopods are protandrous hermaphrodites. Basically, this means that these isopod individuals first mature into males, but can then switch sexes to become females. This can be of a particular advantage to the isopods.
First, a juvenile infiltrates the gills of the fish and begins maturing into a male. Then, when a second juvenile enters the gills it stimulates the original isopod to become a female and the second isopod impregnates her.
At this point, the female crawls from the gill chamber of the host fish up through the throat and to the tongue. It is here that the female then uses her legs to anchor to the tongue of the fish.
Photo Credit: Source
The female isopod then spends the rest of her life breeding and feeding from her new cozy perch. She feeds by sucking the blood from the tongue of the fish. In some instances, like in the case of the rose snapper, the isopod will actually consume the tongue of the fish.
The fish then adapts to its new parasitic tongue, using it almost like a prosthetic.
The female isopods, having lost the ability to swim, will also die if they release their host. Females usually die when their food supply has been diminished, after draining all the blood from the tongue.
While there are many other parasitic isopods that target fish tongues, only C. exigua is thought to actually assume the function of a prosthetic tongue. It is the only known case in the animal kingdom of a parasite functionally replacing a host’s organ.
Maybe you think that this doesn’t seem all that bad for the fish. Well, it is. The process is quite uncomfortable for the host, and when the isopod finally detaches itself or dies, the fish will then starve without a tongue, and eventually die as well.
Photo Credit: Tan Heok Hui via Channel NewsAsia
Even though the isopod goes down with the ship, it has successfully raised a new brood of isopods within the safety of its very own protective den with a continuous supply of food.
Scientists aren’t exactly sure when the young are released from the female, but it is thought around the time when the fish school. This would allow the juvenile crustaceans to infest new hosts, thus starting the cycle all over again.
While these isopods do not infest us, they do attack fish we consume, such as snapper. There have been many cases where people have found these isopods still in their hosts when they are preparing meals or after catching the fish. While they are creepy and bizarre, the only ones that need worry are the fish they infest.
Next time you go fishing or buy a fish to cook for dinner, be sure to check the inside of their mouth for isopods! You just may find a female isopod in place of a tongue!