Silver carp blood cells parameters challenging with Benzocaine as an anaesthetic in fish

Abstract

Anaesthetics are used with increasing frequency in aquculture, mainly to reduce the stress and to prevent mechanical damage to fish during handeling. In this study, we evaluated the efficacy of benzocaine as an anaesthetic in silver carp (Hypophthalmichtys molitrix), in terms of the time required to become anaesthetized ('anesthetic time') and recovery time. In the first experiment, fish were exposed to various doses of benzocaine (20, 40, 60, 80 and 100 mg/L) and temperatures (15, 24 and 30°C). The second experiment examined the effects of duration of exposure to 120 mg/L of benzocaine. In the third experiment, fish were exposed to 60 mg/L at temperatures of 24oC, 27oC, and 30oC. Stages of anaesthesia like increased respiration, erratic swimming and reduced activity of fish were monitored and also ability of fish handling for intra-peritoneal injection was assessed. A benzocaine concentration of 60 mg/L was considered ideal for quickly induci ng total immobilization and fast recovery. A significant relationship between concentration and temperature (P