Efficacy of benzocaine as an anaesthetic for Crucian carp (Carassius carassius).

Objective: To investigate the anaesthetic induction time and concentrations of stress markers in Crucian carp (Carassius carassius) subjected to different concentrations of benzocaine.

Study Design: Prospective experimental study.

Animals: Thirty-six Crucian carp [body weight 368.3 +/- 22.7 g and length 28.1 +/- 1.9 cm (mean +/- SD)].

Methods: Fish were divided into four groups, initially with nine fish per group. Each group was subjected to one of four final concentrations [0, 25, 50 and 100 parts per million (p.p.m.)] of benzocaine. The times to induction of sedation, to pre-anaesthesia and to anaesthesia were recorded according to the behavioural events observed after exposing the fish to benzocaine. At each stage, blood was collected from the caudal vein of three fish of the group, and these three fish were then euthanized. Plasma cortisol and glucose concentrations in the blood samples were measured as indices of stress response.

Results: Induction times for all stages of anaesthesia decreased significantly with increasing concentrations of benzocaine (1678 +/- 103, 475 +/- 73 and 251 +/- 2 seconds for anaesthesia in 25, 50 and 100 p.p.m., respectively). Plasma cortisol and glucose concentrations were significantly lower in the anaesthetized groups than the control group (p < 0.05), and tended to decrease with an increasing dose of benzocaine. The cortisol concentrations (36.1 +/- 5.8 ng dL(-1)) at the anaesthetic stage for the 100 p.p.m. group were significantly decreased compared with the other groups (67.3 +/- 14.9 ng dL(-1) in 25 p.p.m. and 47.6 +/- 2.6 ng dL(-1) in 50 p.p.m.). Differences in glucose concentrations between benzocaine-treated groups were not significant.

Conclusions And Clinical Relevance: In this study, the fish group exposed to 100 p.p.m. benzocaine had a fast induction time for all monitored stages, low circulating cortisol and glucose concentrations and no immediate mortality.