The anesthetic properties of clove oil and tricaine methanesulfonate (MS-222) were tested in a laboratory setting on the southern redbelly dace (Phoxinus erythrogaster), a small cyprinid common to upland streams of the Mississippi River basin. We used southern redbelly dace as a surrogate species to indicate the lowest, most effective anesthetic level for our work with the closely related blackside dace (Phoxinus cumberlandensis), a federally protected species. Concentrations of 20, 40, and 60 mg L-1 clove oil and 20, 40, and 60 mg L-1 MS-222 were used to anesthetize southern redbelly dace at water temperatures of 11, 17, and 21 C, representing a natural range of temperatures encountered in research streams from spring through autumn. For clove oil, induction rates were dependent on dose, temperature, and the interaction between these two variables. Recovery rates, on the other hand, were dependent only on temperature (quicker recovery at warmer temperatures). Clove oil concentrations of 40 and 60 mg L-1 proved to be effective at all three temperatures, inducing stage 4 anesthesia (total loss of equilibrium) at mean times < 3 min while allowing stage 4 recovery (reaction in response to external stimuli) in < 5 min. MS-222 concentrations of 20 and 40 mg L-1 were ineffective for producing anesthesia and the 60 mg L-1 concentration was only slightly effective. No mortalities were observed with either anesthetic. The 40 mg L-1 clove oil concentration was the lowest effective dose at all three temperatures; thus, we recommend this concentration for blackside dace during typical spring, summer, and autumn conditions. Our recent in situ use of 40 mg L-1 clove oil has confirmed its effectiveness and apparent safety for blackside dace.
