Lack of postexposure analgesic efficacy of low concentrations of eugenol in zebrafish.

OBJECTIVE

To test the postexposure analgesic efficacy of low doses of eugenol in zebrafish.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 76 large adult zebrafish (Danio rerio).

METHODS

Fish swimming behavior (median velocity, freeze time, high-speed swimming and distance moved in the vertical direction) was recorded in a 1.6 L video arena before and after exposure to eugenol (0, 1, 2, 5, 10 and 20 mg L). In a second experiment, fish were anesthetized with 2-phenoxy-ethanol and treated with an injection of 5% acetic acid (noxious stimulus), and then exposed to 0, 1, 2 and 5 mg L eugenol. The fish swimming behavior was also recorded.

RESULTS

The higher doses (10 and 20 mg L) reduced the median velocity, high-speed swimming and distance moved in the vertical direction, and increased the freeze time. Zebrafish behavior was not altered by eugenol (1, 2 and 5 mg L) after noxious stimulation.

CONCLUSIONS AND CLINICAL RELEVANCE

The change in the behavior of zebrafish associated with a noxious stimulus can be monitored and is a good model for studying analgesia in fish. Eugenol (10 and 20 mg L) induced zebrafish sedation. The response after a noxious stimulus was not affected by postexposure to lower doses, and thus we cannot recommend its use as an analgesic.