13 September 2010
Three-quarters of the threadfin cardinalfish examined in the waters around Lizard Island have myxosporean cysts around their hearts, according to Holly Heiniger.
Holly, a PhD student and researcher at the University of Queensland and the Queensland Museum, is focusing on myxosporean parasites found in fish of the family Apogonidae, or cardinalfish.
The Myxosporea are a class of microscopic parasites. They have a two-stage life cycle, usually involving an invertebrate, such as a polychaete worm, and a vertebrate, such as a fish, reptile, amphibian or mammal. The parasite releases a different type of spore from each host, and species identification is usually based on the size and shape of the spores released by vertebrate hosts.
Holly is particularly interested in the biology and species richness of species from two genera of myxosporeans, Myxidium and Zschokkella. She will study the morphology (the shapes, structure and anatomy), ecology and phylogenetics (the evolutionary relationships between species) of specimens she finds on the CReefs trip to Lizard Island.
"Specimens from these two genera can appear similar based on morphology, and there's been some contention over which species belong to which genera. My work will focus on revising these two genera, so that the taxonomy accurately reflects the species' phylogenetics," Holly explains.
"We're focusing on parasites in apogonids, or cardinalfish, because they are one of the most diverse fish families on the reef, occupying different behavioural and ecological niches; for example, some species are solitary, while others form schools, and different species have different feeding behaviours," she says.
Many reef fish have a pelagic larval stage: that is, young fish live for a time in the water column of coastal and oceanic waters, some distance from shallow coral reefs. Some apogonids, however, do not have a pelagic stage, because they are mouth brooders – the male fish holds the eggs in his mouth to incubate them.
"We're looking at how mouth brooding behaviour in apogonids affects parasite ecology, compared to fish that have pelagic larval stages," Holly explains.
Holly is working with the team of parasitologists on Lizard Island to catch apogonids, and examine specimens through microscope work, taking measurements of all the morphological characters. Samples of the parasites' genetic material will also be analysed, using small subunit of the ribosomal DNA to assist in identifying parasite species.
"On this trip, we've found a number of Myxidium and Zschokkella species in apogonids' gall bladders," Holly says.
"We've also found a high prevalence of myxosporean parasites of the genus Kudoa in the threadfin cardinalfish, Apogon leptacanthus. Approximately 75 to 80 per cent of these fish are infected with cysts surrounding their hearts caused by a species of Kudoa; that's quite a high infection rate."
Holly's work is not, for the moment, concerned with the pathology caused by the myxosporeans, but is focusing on their host-parasite relationships, diversity and biogeography in marine fish.