25 July 2010

Tokolosh discovered at the Aquarium!

David Vaughan
Heterocotyle tokoloshei, the tokolosh worm

David Vaughan is the Two Oceans Aquarium’s aquatic animal health researcher. He conducts research into various fish parasites and other health issues affecting aquatic animals at the Aquarium.

The tokolosh is a mythical South African character, best known from the traditional Xhosa and Zulu cultures as the shape-shifting dwarf-like trouble maker that is invisible to adults. The tokolosh is blamed for most mischief and the unexplained and it is therefore fitting that the discovery of a cryptic parasite infecting our giant short-tail stingrays in the I&J Predator Exhibit, and found only in South Africa, was named after him.

For some time I had been baffled by the sudden onset of mysterious symptoms in the rays, including loss of appetite and heavy breathing, but with no outward signs of any stress or injuries. In fact, the rays appeared to be in generally good condition.

The mystery was solved when one of the rays, Olive, was removed from the I&J Predator Exhibit for closer observation in the quarantine area.

Samples of sediment from the ray’s holding tank revealed masses of microscopic eggs belonging to a monogenean flatworm parasite … But where were these worms? Most monogeneans are ectoparasites, which means they are in constant contact with the external environment. The worms on the ray were therefore not likely to be intestinal and had to be in direct contact with the seawater.

I opted to test out a new non-invasive prospecting method of sampling for monogeneans that I had been working on for some time. The method included the experimental application of a drug known to effect monogeneans and other worms, but is given orally while the ray is under general anaesthetic.

The prospecting method was successful, and I recovered approximately 400 000 individual worms that had been living in the ray’s gill tissue. Here the worms could make use of a great food supply by feeding on the gills, while still being in direct contact with the seawater, but remaining invisible to the outside world.

Closer inspection of the microscopic worms revealed that they were a new species to science, a Heterocotyle species belonging to the family Monocotylidae. In collaboration with Dr Leslie Chisholm, a well-known specialist on monocotylid monogeneans, from the South Australian Museum, the new species was described and published in the international scientific journal Acta Parasitologica and was given the name Heterocotyle tokoloshei, the tokolosh worm.

The tokolosh worm was investigated further at the Aquarium to learn more about its lifecycle. Only when I knew more, could I determine what the best treatment strategy would be to control further outbreaks, and to design preventative treatment protocols for any new rays that we might collect in future. The biological information obtained from the results of lab experiments, to determine the effects of water temperature on egg hatching and re-infection rates, provided data for the design of what’s called an integrated pest management strategy, which is already being used with great success.

I can rest easy now knowing that our rays are happy, but this encounter has me considering putting my bed on bricks to avoid further confrontations!

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