AUG 02, 2016 09:50 AM PDT

Common Parasite may be Affecting Zebrafish Research

WRITTEN BY: Carmen Leitch
A new report in the Journal of Fish Diseases has raised questions about the husbandry of zebrafish in laboratories everywhere.  The authors suggest that a common parasite could be confounding the results of behavioral assays performed using the fish; critics say not so fast.
In this photo from Oregon State University College of Veterniary Medicine blog, two zebrafish are shown. The bottom fish is infected with a type of Pseudoloma. / Credit: OSU
Zebrafish are a commonly used experimental model organism. They develop very rapidly and are transparent for the first few days of development (drug treatment keeps them transparent for even longer) and they are hardy animals; all those qualities make them good for laboratory research.
Because they are such highly social animals, they are also often used in behavioral studies. It’s been speculated that they’re even better for psychological testing than rodents for some human behaviors.

The new work shows however, that Pseudoloma neurophilia, a neural parasite, has a dramatic effect on zebrafish behavior. The researchers have observed that individual fish carrying a P. neurophilia infection swim closer to one another than non-infected fish do.  That behavior has also been associated with increased anxiety and stress in fish. Lead study author Sean Spagnoli, a veterinary surgeon, explains that the finding casts doubt on data obtained in from previous experiments. If the infection itself might have been affecting shoaling behavior, it’s difficult to interpret the results.

According to 2015 data from the Zebrafish International Resource Center (ZIRC), up to half of all lab facilities might be using some zebrafish infected with the parasite. However, only 28 facilities sent zebrafish to ZIRC for health checks in that year. According to Spagnoli, infection rates hover around 7-10% within a facility, but some tanks have no infected zebrafish while others have many.

“The paper is great, as it raises some doubts about the way behavior may be used to study brain function in zebrafish,” Robert Gerlai, a behavioral geneticist at the University of Toronto Mississauga in Canada, told Nature News. He also advised to remain cautious, as this was only a single study.
Effects of Pseudoloma neurophilia exposure on shoaling behaviour of zebrafish. Exposure to P. neurophilia significantly decreased the average interfish distance with 12 shoals (tanks), six exposed and six controls. *P = 0.026, U-test. / Credit: Journal of Fish Diseases
Gerlai raised concerns about the work as well. He notes that Spagnoli’s team used low-tech methods to measure their fish shoals – rather than using a continuous tracking system, they simply used screen snapshots and measured the distance between each fish. He also added that the researchers didn’t assay for what else may have been affecting the zebrafish.

A geneticist at University College London, Elena Dreosti, told Nature News that the paper’s shows small effects from weak data. “Considerable additional work is needed to know if this is likely to have a significant impact on the type of behavior research that is done by the community working with zebrafish,” she explained.

While Spagnoli agreed that he proven that the parasite was responsible for the alteration in behavior, he thinks the results from their low-tech methodology are enough to be alarming. He hopes that zebrafish investofgators will start taking the time to screen for this parasite. In the meantime he’s assessing what another common microbe in zebrafish facilities, Mycobacterium chelonae, does to behavior.

If you'd like to see why investigators like working with zebrafish, check out the video below that shows how rapidly they develop over 24 hours, and how easy it is to see inside them.


Sources: ZIRC, Nature, Journal of Fish Diseases
About the Author
  • Experienced research scientist and technical expert with authorships on 28 peer-reviewed publications, traveler to over 60 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
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