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Catch of the day in Borneo uncovers new species

Scientists have travelled to Borneo to study parasites infecting sharks and stingrays. The study has led to the discovery of many new species, and the data has been used to help Australian aquaria control the spread of parasite infections in the sharks and stingrays they have on display.

An ongoing project investigating the biodiversity of parasites on sharks and stingrays has seen two researchers from the South Australian Museum travel as far as Borneo to work with local fishermen in finding the freshest and most accurate samples. The researchers – Parasitology Collection Manager Dr Leslie Chisholm and Head of Biological Sciences Associate Professor Ian Whittington – were invited to be a part of the study because of their specialist knowledge in monogenean parasites.

New species of both the host animals and the parasites have been discovered during the project and the data have been useful for services such as helping public aquaria control worm infections, improving the health of animals on display.

The project is funded by United States National Science Foundation’s Biotic Surveys and Inventories Program, and its Chief Investigator is Professor Janine Caira from the University of Connecticut, USA. The parasitologists were thrilled to be invited to be a part of the study as they could use their skills to better map the biodiversity of the region and there was a strong likelihood of uncovering many new species. Only a very small number of records of metazoan parasites existed for sharks and rays of this geographic region before the study.

They worked with fish taxonomists from eight different institutions in the USA, Australia, Indonesia and Malaysia, focusing on the elasmobranchs (sharks and rays) and their metazoan parasites from inshore and freshwater habitats of the island of Borneo. A total of six surveys were conducted over a 6-year period in Malaysian Borneo (2002 – 2004) and Indonesian Borneo (2006 – 2008) during which time approximately 900 specimens of sharks and rays were collected. These were infected by a multitude of metazoan parasites belonging to at least four animal phyla, including all three major groups of platyhelminths (external and internal fluke and tapeworms), as well as annelids (leeches), nematodes and arthropods.

Associate Professor Whittington and Dr Chisholm travelled to Borneo to find and recover the best samples of parasite to bring back to Australia.

“In the small villages, we collected fresh host material from local fisherman who had brought in live or recently dead fish,” said Dr Chisholm.

“Once the host dies, the parasites tend to die as well and because the water temperature is pretty high, things start decomposing quite quickly. The fishermen would go out for us in their little boats overnight and we’d say “we would like these fish species,” then we’d dissect the animals they brought in and look for the parasites.”

The scientists analysed their specimens and data back in our Museum laboratories and continued studying organs and tissues of sharks and rays sent over from the other scientists during other collections. They uncovered some very interesting findings:

“We found that more rays were infected than sharks,” said Dr Chisholm. “This was the first study to look at so many animals and the number of infected sharks was very low ... around six per cent. This has been found in the past but we never knew if it was a true relationship because of the small samples of host animals.”

“This might be a matter of habitat – most rays tend to sit on the bottom and if the eggs of the parasites are shed and land on the sea bed and then hatch out, the parasite larvae might have a better chance of infecting another ray versus a shark, which are commonly swimming around above the sea bed.”

Parasites are important to understand in the context of marine ecosystems globally. They play an important role in the life cycle of marine creatures and have a commercial impact as well.

“On top of doing surveys, I’ve done a lot of work on the biology of the parasites looking at things like how long they take to develop and seeing how they infect hosts, as well as what treatments we can use to get rid of them,” says Dr Chisholm. “So if you know what’s living on the sharks and rays in the wild, then you have a better idea of how to help animals in tanks.

“Parasites can be particularly troublesome in the public aquaria trade, especially on rays. I get a lot of the curators of aquaria around the world saying, “I’ve got a sick ray here, can you identify the parasite? Is there a chance it could infect other fish in the tank and what can we do to get rid of it?””

Dr Chisholm says animals in an aquarium are more likely to get infections because they are in an environment with more stressors.

“Often aquarists go out into the wild to collect these animals. If they put them right into the display tanks without screening them first, they can have problems if the fish was already infected with a few parasites. High explosions of infections can happen for a few reasons. Since the fish are in a recirculating system, the numbers of parasite eggs and larvae can build up to incredible levels very quickly. Also the fish may be more susceptible to infection if they are stressed by being crowded close together, or by people banging on the glass or if the water temperatures are higher than what they’re used to.”

Our parasitologists are passionate about their work, helping us understand and protect our environment and the host animals.

Rather than stay cooped up in a lab, they have had incredible adventures around the world in their profession.

“We’ve been to other amazing places like Mexico and in Australia, Heron Island, Lizard Island, Darwin and Perth, looking at so many different species and working with all sorts of great people,” says Dr Chisholm.

The international data for the shark and stingray parasite project have been published progressively. A summary document will be published when the data is collated.

South Australian Museum