Evaluating the efficacy of benzocaine and the effects of anesthesia with it on the blood factors of goldfish (Carassius auratus)

Common operations during reproduction and breeding or during research studies often cause stress and physiological responses in fish, which subsequently lead to adverse effects such as immunosuppression, delayed growth, and death. The objectives of this experiment were to evaluate the efficacy of benzocaine as an anesthetic in goldfish (Carassius auratus). Moreover, the effect of anesthesia with effective concentrations of benzocaine and stress caused by manipulation on hematological indicators was studied.

For this purpose, ten fish individually were exposed to 50, 75, 100, 125, 150 and 200 mg/L benzocaine, and time to induction (deep anesthesia) and recovery from anesthesia were measured. In the second experiment, 7 fish were deeply anaesthetized with 125 and 150 mg/L benzocaine. Subsequently, Fish were subjected to stress by acute handling, blood sampling and maintaining them out of the water for 2 min. for assessing possible stress effects caused by acute handling, blood was collected as described above without anesthesia. In control group, fish immediately after netting with their head covered with wet cloth to reduce stress, blood collection was performed by cutting caudal peduncle and lasted less than 15 s.

At concentration of 50 mg/L, benzocaine failed to induce deep anesthesia in fish within the 10 min exposure period whereas at concentrations of 125, 150 and 200 mg/L, all the fish were anaesthetized within 3 min of exposure. Induction and recovery times for benzocaine were significantly dependent on concentrations (P<0.05). Hematological results between groups showed no significant changes in white blood cell count and hematocrit level. Acute handling caused significant increase in hemoglobin, red blood cell count, serum glucose and cortisol levels compared to control and anaesthetized group (P<0.05).

This study demonstrates that rapid induction of deep anesthesia with a relatively high concentration of benzocaine (125 mg/L) block the stress-induced cortisol response with the lowest effects on the hematological and serum biochemical indices in gold fish and therefore would be recommended as eligible dose for handling and hematological studies in this species.