Wow. For my dissertation I’m studying the behavioral effects of a trematode parasite (Euhaplorchis californiensis or EUHA) infecting the brains of California killifish. I was dissecting a killifish to count the number of parasites in its brain case and discovered that this particular head was home to two very large isopods.

The picture below is a California killifish brain (center) and 2 isopods (left and right). The brain is a bit beat up because I was searching in the crevices for EUHA. The isopod on the right is missing its back end.

These parasitic isopods were found underneath the fish’s operculum, which I suppose is the fish equivalent of our cheeks. Look at the size of those isopods! Can you imagine having parasites the size of your brain living in your cheeks!

I believe that findings such as this support my argument that researchers should be paying more attention to the parasites in their study organisms. These parasites were not visible externally, but were easy to find after a quick dissection. It’s hard for me to imagine that parasites of this size living off of a small fish have no effects on its behavior or fitness. I know that learning parasitology may seem daunting, but just a little parasitological knowledge would likely provide major insights into explaining individual differences in behavior. ::Jumps off soapbox::