Parasitic infection may have spoiled zebrafish experiments

From Nature:

O. LOUIS MAZZATENTA/NGC

A parasitic infection lurks within many populations of zebrafish.

A common parasite that infects laboratory zebrafish may have been confounding the results of years of behavioural experiments, researchers say – but critics say the case isn’t proven.

Like the rat, the zebrafish (Danio rerio) is used in labs worldwide to study everything from the effects of drugs, to genetic diseases and disorders such as schizophrenia and autism. Since both zebrafish and people are highly social, researchers think that zebrafish may be a better lab model for some human behaviours than rodents.

Zebrafish demonstrate their preference for each other by clustering into shoals – a social behaviour that researchers  measure when they want to test how drugs affect zebrafish stress and anxiety levels, as a proxy for potential human responses. But this behaviour can change when fish are infected with a neural parasite called Pseudoloma neurophilia, scientists from Oregon State University in Corvallis report in a paper published on 11 July in the Journal of Fish Diseases1.

The team say that individual fish infected with P. neurophilia swim closer to each other than do non-infected fish, a behaviour that is also associated with increased stress and anxiety. The finding casts doubt on results from previous experiments, says lead study author Sean Spagnoli, a veterinary surgeon – since the infection may have scrambled researchers’ interpretations of shoaling behaviour.

Spagnoli first heard that a parasite was infecting many laboratory zebrafish when he was working at the Zebrafish International Resource Center (ZIRC) in Eugene, Oregon – a central repository which sends out zebrafish strains to researchers and also tests zebrafish health. P. neurophilia settles in the brain, spinal cord and nerves of zebrafish.

“The paper is great, as it raises some doubts about the way behaviour may be used to study brain function …

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