Metomidate has been reported effective as an anesthetic in a variety of commercially important food fish. Significant species variability in dose response and variability due to lowered water pH have been reported. This study investigates metomidate's suitability as a general anesthetic in five species of popular ornamental freshwater fish, Knifefish (Xenanystus nigri), Blue gourami (Trichogaster trichopterus sumatranus), Blue acaris (Aequidens portalegrensis), Platies (Xiphorous maculatus) and Goldfish (Carassium quratus). Groups of healthy fish placed in various concentrations of drug were monitored for anesthetic plane based on standardized assessment of activity and reflex responses. Water temperature and pH were monitored. Optimal doses were determined based upon induction and recovery times correlated with behavior of the fish during the procedure. Significant differences related to acclimation pH were observed. The drug was not suitable for use in Knifefish (prolonged induction and recovery) or Blue gouramis (high mortality) which were acclimated to acidic conditions normally beneficial for these species. Blue acaris acclimated to neutral conditions were sedated in 10 ppm and anesthetized to surgical plane in 30 ppm with an average induction time of 7.5 minutes (S.E. 0.5 min.). Results with Platies acclimated to acid conditions did not replicate previously published results with the same species. This study found doses between 20 and 30 ppm necessary to achieve anesthesia in less than 10 minutes in this species at pH 6. At pH 7.8, 10 ppm provided surgical planes in under 10 min. Goldfish at pH 6.2 were reliably anesthetized with 20 ppm but did not survive 30 ppm induction.

All recoveries were associated with hyperexcitability. The pH of water used for induction was of critical importance and the impact upon cortisol levels in light mammalian studies implicating a block of 11 hydroxylation in cortisol synthesis may not be beneficial.