Behavioral Characteristics of Adult Zebrafish (Danio rerio) after MS222 Anesthesia for Fin Excision

Abstract

The health of laboratory animals is an ethical responsibility of researchers and a critical determinant of experimental outcome. Therefore, all husbandry procedures should be evaluated for their effects on mortality, behavior, and physiology to maximize animal welfare and minimize experimental variability. For adult zebrafish, the excision of a small portion of the caudal fin (that is, 'fin clipping') under MS222 anesthesia is a common procedure to obtain tissue for genotyping. The potential effect of this procedure on behavioral and physiologic assays of feeding, anxiety, and stress has not previously been assessed. Here, we evaluated feeding behavior, anxiety-associated behaviors, and physiologic indicators of stress at multiple time points within 24 h after performing a standard fin-clip procedure under MS222 anesthesia. Within 1 h of the procedure, fin-clipped fish showed a mild increase in anxiety and exhibited reduced feeding; however, these effects were short-lived, and the fish exhibited baseline levels of anxiety and feeding by 6 and 24 h after fin clipping. Together with the zebrafish's ability to regenerate fin tissue and the low mortality associated with fin clipping, our data support the continued practice of this technique under MS222 anesthesia as a routine husbandry procedure that is unlikely to alter experimental outcomes related to feeding, anxiety, or stress.

Figure 1.

Zebrafish show normal anxiety levels within 6 h of fin clipping. (A) Schematic of novel tank. Dashed line indicates the bottom 1/3 and top 2/3 of the tank. (B) Mean latency to normalize position in novel tank. (C) Mean number of freezes per trial. (D) Mean duration per freeze. FC, fin-clipped; CON, sham-procedure controls; dots represent individual fish (black, female; red, male); error bars indicate the SEM for all fish tested. Values at each time point were compared (t test; †, P < 0.01; ‡, P < 0.001) between CON and FC groups.

Figure 2.

Cortisol levels are unaffected by fin clipping. Mean cortisol levels were measured by ELISA. Dots represent individual fish (black, female; red, male); error bars indicate the SEM for all fish tested. CON, control; FC, fin-clipped.

Figure 3.

Zebrafish exhibit normal feeding within 6 h of fin clipping. (A) Schematic of feeding assay. (B) Mean latency to eat the flake food. Dots represent individual fish (black, female; red, male); error bars indicate the SEM for all fish tested. Values at each time point were compared (t test; ‡, P < 0.001) between control (CON) and fin-clipped (FC) groups.