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Alfaxalone, a synthetic neuroactive steroid, has been tested as an immersion anesthetic in ornamental fish, but its safety and efficacy in sport fish have not been investigated. In the current study, we compared the physiologic and behavioral effects of alfaxalone with those of tricaine methanesulfonate (MS222) for anesthesia of rainbow trout (Oncorhynchus mykiss) via water immersion. We also analyzed alfaxalone-exposed tissues to determine residue clearance times. Fish were anesthetized for 10 min by immersion in low-dose alfaxalone (Alow; 5 mg/L induction, 1 mg/L maintenance), high-dose alfaxalone (Ahigh; 5 mg/L induction, 2 mg/L maintenance), or MS222 (MS; 150 mg/L induction, 100 mg/L maintenance). Fish received all 3 treatments, separated by a washout period of at least 18 d in a blinded, complete crossover design. We hypothesized that immersion in Alow or Ahigh would provide a stable plane of anesthesia in rainbow trout, with dose-dependent time to recovery, and that opercular rates and depths of anesthesia would be equivalent to that of MS222. The time to anesthesia induction was longer for alfaxalone than MS222 but averaged less than 100 s. The time to recovery from anesthesia was also longer for alfaxalone than MS222, with significantly shorter recovery time for Alow than for Ahigh. All treatments decreased opercular rate and response to noxious stimuli. Alfaxalone residue clearance was greater than 80% from all tissues within 1 h, greater than 99% from muscle within 4 h, and 100% from all tissues within 36 h after exposure. We conclude that alfaxalone immersion at 5 mg/L for induction and 2 mg/L for maintenance provides a safe, viable alternative to MS222 for the anesthesia of rainbow trout.

Alfaxalone anesthesia and residue clearance profiles in rainbow trout Alfaxalone, a synthetic neuroactive steroid, has been tested as an immersion anesthetic in ornamental fish, but its safety and efficacy in sport fish have not been investigated. In the current study, we compared the physiologic and behavioral effects of alfaxalone with those of tricaine methanesulfonate (MS222) for anesthesia of rainbow trout (Oncorhynchus mykiss) via water immersion. We also analyzed alfaxalone-exposed tissues to determine residue clearance times. Fish were anesthetized for 10 min by immersion in low-dose alfaxalone (A(low); 5 mg/L induction, 1 mg/L maintenance), high-dose alfaxalone (A(high); 5 mg/L induction, 2 mg/L maintenance), or MS222 (MS; 150 mg/L induction, 100 mg/L maintenance). Fish received all 3 treatments, separated by a washout period of at least 18 d in a blinded, complete crossover design. We hypothesized that immersion in A(low) or A(high) would provide a stable plane of anesthesia in rainbow trout, with dose-dependent time to recovery, and that opercular rates and depths of anesthesia would be equivalent to that of MS222. The time to anesthesia induction was longer for alfaxalone than MS222 but averaged less than 100 s. The time to recovery from anesthesia was also longer for alfaxalone than MS222, with significantly shorter recovery time for A(low) than for A(high). All treatments decreased opercular rate and response to noxious stimuli. Alfaxalone residue clearance was greater than 80% from all tissues within 1 h, greater than 99% from muscle within 4 h, and 100% from all tissues within 36 h after exposure. We conclude that alfaxalone immersion at 5 mg/L for induction and 2 mg/L for maintenance provides a safe, viable alternative to MS222 for the anesthesia of rainbow trout.

Systemic isosporosis (formerly atoxoplasmosis), is a protozoal infection that causes death in nestling and fledgling passerine birds impacting ex situ breeding and reintroduction programs. Because current antemortem diagnostic tests lack sensitivity, a qPCR was developed for detection of Isospora spp. using primers and a fluorescent-tagged MGB probe targeting the large subunit (28s) ribosomal RNA gene (assay efficiency = >100%; sensitivity =