Bluegill fish (Lepomis macrochirus) are a popular sportfish across North America. Research involving bluegill has focused mainly on locomotion, environmental monitoring, bioaccumulation, and toxicology. With fish becoming more popular research models, bluegill use may increase. Consideration for sedation and anesthesia in bluegill is lacking. MS-222 is a commonly used anesthetic in fish that requires a 21-d washout period before entry into the food chain. Other, safer options for anesthesia should be available. In this study, we first determined a suitable MS-222 dose for general anesthesia, then compared it with 2 different concentrations of alfaxalone (5 and 10 mg/L). Both concentrations of alfaxalone were adequate to reach the desired anesthetic plane, although time to effect was dose-dependent and longer in these groups when compared with MS-222. Time to recovery was also prolonged in both alfaxalone groups compared with the MS-222 group. We also assessed anesthetic degradation in the water bath over time. In this study, we show that sedation with alfaxalone at 5 and 10 mg/L is just as effective as MS-222 with no degradation of either anesthetic over the time measured.
Tactile response test using blunt forceps to apply the noxious stimulus to the caudal fin.
Experimental setup. (A) Overview showing the anesthesia tank on the left and the recovery tank on the right. The bluegill in the recovery tank has not yet regained righting reflex. (B) Image capture computer using EthoVision XT to track movement while in recovery tank.
Time in seconds to various anesthetic events. Median for each anesthetic concentration is represented by the following symbols: O = MS-222, + = alfaxalone 5 mg/L, X = alfaxalone 10 mg/L. Boxplot represents the median and the IQR, the marker represents the mean, and the whiskers denote observations falling within a range equal to the first quartile – 1.5 IQR and the third quartile + 1.5 IQR. Small markers outside the whiskers represent extreme observations beyond this range. LORR shows the time to loss of righting reflex for each anesthetic group, which was significantly shorter for the MS-222 group than either alfaxalone group (O = 69.5 s, + = 204.5 s [P < 0.0001], X = 119.5 s [P < 0.0140]). LOSR shows the time to loss of the startle response, which was significantly shorter in the MS-222 group than either alfaxalone group (O = 79.5 s, + = 227.5 s [P < 0.0001], X = 176.0 s [P < 0.0001]). LOTR shows the time to loss of tactile response, which was significantly shorter for the MS-222 group than either alfaxalone group (O = 109 s, + = 326.5 s [P < 0.0001], X = 226.0s [P < 0.0001]).
Time in seconds to OM score. Median for each anesthetic concentration is represented by the following symbols: O = MS-222, + = alfaxalone 5 mg/L, X = alfaxalone 10 mg/L. Boxplot represents the median and the IQR, the marker represents the mean, and the whiskers denote observations falling within a range equal to the first quartile – 1.5 IQR and the third quartile + 1.5 IQR. Small markers outside the whiskers represents extreme observations beyond this range. Minimum OM shows the time to return to normal OM score in the recovery tank, which was not significant between any of the groups (O = 226.5 s, + = 279.0 s, X = 301.5 s). Maximum OM shows the time it took each fish to reach their maximum (highest) OM score. Fish in the MS-222 group reached their maximum score (shallow to absent) more quickly than did the fish in either alfaxalone group (decreased to shallow) (O = 36.0 s, + = 212.5 s [P < 0.0001], X = 159.5 s [P = 0.0002]).
Time in seconds to return to normal after movement to recovery tank. Median for each anesthetic concentration is represented by the following symbols: O = MS-222, + = alfaxalone 5 mg/L, X = alfaxalone 10 mg/L. Boxplot represents the median and the IQR, the marker represents the mean, and the whiskers denote observations falling within a range equal to the first quartile – 1.5 IQR and the third quartile + 1.5 IQR. Small markers outside the whiskers represent extreme observations beyond this range. ROSR shows the time to return of self-righting reflex for each anesthetic group, which was significantly shorter for the MS-222 group than either alfaxalone group (O = 109.0 s, + = 305.0 s [P = 0.0008], X = 368.0 s [P < 0.0001]). RONS shows the return to normal swim, which was significantly shorter for the MS-222 group than either alfaxalone group (O = 282.5 s, + = 839.5 s [P < 0.0001], X = 866.5 s [P < 0.0001]).
Minimum acceleration per minute during the 10-min recovery. Note the significant drop in acceleration in the MS-222 group at the 5-min mark. This coincides with the median recovery time of 4.75 m and normal bluegill resting behavior. Several bluegill in the alfaxalone groups were not fully recovered at the end of the 10 min.
Maximum acceleration per minute during the 10-min recovery. Note the significant acceleration in the MS-222 group slightly before the 5-min mark. This coincides with return to normal swim and a subsequent possible excitatory phase. Acceleration rapidly drops by minute 6 and coincides with normal swim behaviors in bluegill. Several bluegill in each alfaxalone group were not fully recovered at the end of the 10 min. No excitatory phase was noted in these groups during recovery.
Distance moved per minute during the 10-min recovery. The peak at minute 4 in the MS-222 group correlates with the RONS time and an excitatory phase observed around this time. No excitatory phase was seen in either alfaxalone group. Several fish had not fully recovered by the end of the 10 min.
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