Tattoo on the heart


17 November 2010
Parasites can sign their name across the hearts of their fish hosts, leaving clues for scientists about patterns of infection, according to University of Queensland Associate Professor Thomas Cribb.
Tom is working with a team of scientists studying parasitic flatworms, commonly known as flukes, in fish on the CReefs expedition to Heron Island.
Most flukes live in the intestines and stomach of their fish host but one group, the blood flukes, lives right in the circulatory system, usually inside the heart. They lay their eggs there, and these eggs are usually carried to the gills, where they hatch and escape from the fish. Tom has recently discovered, however, that some of the eggs can get lost and end up trapped in the heart of the fish instead.
"We keep finding encapsulated blood fluke eggs in the heart tissues of butterfly fishes that do not have any adult worms living in other organs," he says.
"The adult worms are rare, but these old, dead eggs are common – which tells us that almost all the butterfly fish species have a history of infection with the blood flukes.
"It could have been a year or more since the fish was infected, and the adult worms lived out their lives and died – but the eggs are still there, like a tattoo. The eggs may very slowly degenerate, but the fish may never entirely get rid of them," he says.
Tom says this gives researchers clues to the distribution of the flukes.
"We're starting to use this method on other species of fishes when we're not sure if they have been host to parasites.
"We haven't found an adult blood fluke in the emperor fish from around Heron Island, for example – but we will keep looking, because we're finding old eggs in the heart, which suggests the emperor is a host for an unknown blood fluke," he explains.
"It's an interesting way of finding evidence of where infections have been in the past," he says.