The common neural parasite Pseudoloma neurophilia is associated with altered startle response habituation in adult zebrafish (Danio rerio): Implications for the zebrafish as a model organism

Abstract

The zebrafish’s potential as a model for human neurobehavioral research appears nearly limitless despite its relatively recent emergence as an experimental organism. Since the zebrafish has only been part of the research community for a handful of decades, pathogens from its commercial origins continue to plague laboratory stocks. One such pathogen is Pseudoloma neurophilia, a common microparasite in zebrafish laboratories world-wide that generally produces subclinical infections. Given its high prevalence, its predilection for the host’s brain and spinal cord, and the delicate nature of neurobehavioral research, the behavioral consequences of subclinical P. neurophilia infection must be explored. Fish infected via cohabitation were tested for startle response habituation in parallel with controls in a device that administered ten taps over ten minutes along with taps at 18 and 60 minutes to evaluate habituation extinction. After testing, fish were euthanized and evaluated for infection via histopathology. Infected fish had a significantly smaller reduction in startle velocity during habituation compared to uninfected tankmates and controls. Habituation was eliminated in infected and control fish at 18 minutes, whereas exposed negative fish retained partial habituation at 18 minutes. Infection was also associated with enhanced capture evasion: Despite the absence of external symptoms, infected fish tended to be caught later than uninfected fish netted from the same tank. The combination of decreased overall habituation, early extinction of habituation compared to uninfected cohorts, and enhanced netting evasion indicates that P. neurophilia infection is associated with a behavioral phenotype distinct from that of controls and uninfected cohorts. Because of its prevalence in zebrafish facilities, P. neurophilia has the potential to insidiously influence a wide range of neurobehavioral studies if these associations are causative. Rigorous health screening is therefore vital to the improvement of the zebrafish as a translational model for human behavior.

Expansion of the Known Host Range of the Microsporidium, Pseudoloma neurophilia

“…In addition, we provide an example of a natural infection associated with clinical disease in a population of laboratory fish, P. promelas. Previous studies have demonstrated the impact of P. neurophilia on zebrafish on common research endpoints such as behavior 19 and fecundity. 20 Similar studies need to be performed on other fish species to determine the impact of nonprotocol-induced variation due to subclinical P. neurophilia infection when they are used in research.…”

Facility Design and Health Management Program at the Sinnhuber Aquatic Research Laboratory

“…5,6 For example, a recent study indicated that background infections could impact zebrafish behavior. 7 One of the most tangible benefits is increased insurance against a catastrophic colony loss due to a virulent pathogenic outbreak. Although the number of serious pathogens affecting zebrafish continues to increase, diagnostic technology has advanced to the point that there is no longer an excuse to not stay on top of it.…”

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

“…More commonly, it is associated with reduced growth and decreased reproductive fitness. 18 Infection with this organism was recently shown to alter behavioral testing conducted with infected fry, 19 and intramuscular granuloma development and myonecrosis associated with infection may display autofluorescence interfering with imaging studies. 20 This agent can be vertically as well as horizontally transmitted, and most currently used protocols for embryo surface disinfection with sodium hypochlorite do not prevent horizontal transmission to offspring.…”