Efficacy of Chemical Sedatives and Electroanesthesia in Sedating Hybrid Striped Bass and Largemouth Bass

Fisheries professionals sedate fish for a variety of purposes, ranging from simple handling to invasive surgical procedures. Currently, there are few sedative options available to fisheries professionals that are safe, effective, and practical to use.  Tricaine methanesulfonate (MS-222) is currently approved by the U.S. Food and Drug Administration for use as a fish sedative, but it is only approved for four families of fishes and users must adhere to a 21-day withdrawal period.  Carbon dioxide (CO₂) is a low regulatory priority drug that can be used as a fish sedative, but it can be difficult to apply safely and uniformly in the field.  Benzocaine and eugenol are currently being investigated for use as immediate-release fish sedatives, but neither is currently approved for such use.  An alternative option is the use of electricity to temporarily immobilize fishes.  Although the efficacy of chemical sedatives has been investigated for some fishes, few studies have assessed their efficacy in side-by-side comparisons or compared them with ‘electroanesthesia’.  Accordingly, we evaluated the use of MS-222 (150 mg/L), CO₂ (~400 mg/L) benzocaine (150 mg/L), eugenol (60 mg/L), and electroanesthesia (30 Hz, 60-100 V, 25%, 3 sec) to induce hybrid striped bass (HSB, 510 ± 12 g, mean ± SE) and largemouth bass (LMB, 508 ± 21 g) to Stage IV sedation (loss of equilibrium, muscle tone, and responsiveness to visual and tactile stimuli; opercular rate slow but steady).  For both taxa, induction times were shortest using electroanesthesia (HSB = 0.23 ± 0.02 min, LMB = 0.24 ± 0.01 min) and longest using CO₂ (HSB = 2.56 ± 0.10 min, LMB = 3.56 ± 0.17 min); induction times for other chemical sedatives varied, but were under 2 min.  Recovery times varied among sedatives and taxa.  For LMB, recovery was significantly longer for eugenol (4.00 ± 0.31 min post-induction) than for the other sedatives, which were comparable and occurred in ~2-3 min.  HSB exhibited a similar pattern in that recovery times were also longest for eugenol (5.20 ± 0.24 min post-induction), but eugenol was not significantly different from benzocaine (3.95 ± 0.23 min post-induction).  Benzocaine was also equivalent to all other sedatives which yielded recovery times of ~3-4 min.  Our research suggests electroanesthesia may be a suitable tool for quickly inducing sedation in largemouth bass and hybrid striped bass, however, all of the sedative options evaluated were effective in sedating fish within reasonable time frames at the doses/strengths used.