Abstract
Cyprinid fish farming is a growing sector of the aquaculture industry in the United States, producing fish for ornamental purposes, food, and bait.3 Efficient, safe, and predictable methods of anesthesia are needed to improve handling, transportation, and manipulation of cyprinids. Currently, the most commonly used and only FDA-approved fish anesthetic is tricaine methanesulfonate (MS-222), commonly delivered in a water bath.1 Alfaxalone, a progesterone analogue, is a neurosteroid, which produces anesthesia and muscle relaxation by interacting with the gamma aminobutyric acid (GABA) receptor.2 It is currently registered in several countries for intravenous induction and maintenance of anesthesia in dogs and cats.4,6 There are several reports describing induction and maintenance of anesthesia in fish with alfaxalone as an immersion agent.5,7 The objective of this study was to evaluate the efficacy of a single induction dose and two maintenance doses of alfaxalone delivered by water immersion in the anesthesia of koi (Cyprinus carpio) by investigating dose-related behavioral and physiological responses. We hypothesized that the induction dose (10 mg/L) and both maintenance doses (1 mg/L and 2.5 mg/L) would be safe and sufficient both to induce and maintain stage IV anesthesia. Six adult koi (Cyprinus carpio) with a median weight of 344.5 g (range: 292.0–405.0 g) were exposed to a single induction dose (10 mg/L) and two maintenance doses (2.5 mg/L and 1.0 mg/L) of alfaxalone in a within-subject complete crossover design. Induction and recovery times were measured, and both behavioral and physiological data were collected before and every 5 minutes during and after anesthesia. Serial analysis of acid-base balance and blood lactate concentrations were measured before, during, and after anesthesia to assist with the evaluation of physiological responses to anesthesia in each fish. Median induction time after immersion at an alfaxalone concentration of 10 mg/L was 5.4 min (range: 3.4–9.1 min). Both maintenance (1.0 mg/L and 2.5 mg/L) doses were capable of sustaining the fish at stage IV anesthesia during the 20 min test period, with median recovery times being 11.8 min (range: 1.9–31.8 min) and 26.4 min (range: 16.3–59.6 min), respectively. Median blood pH decreased significantly (p ≤ 0.05) when comparing fish sampled before anesthesia to those sampled at the end of the 20-minute test period. Blood lactate after anesthesia was significantly increased (p ≤ 0.05) in all fish sampled regardless of the maintenance dose. Immersion administration of alfaxalone provided a safe and effective anesthetic protocol for koi.
References
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