Evaluation of quinaldine anesthesia in common carp (Cyprinus carpio): Induction, recovery, and physiological responses.

Quinaldine is a commonly used anesthetic agent in aquaculture for minimizing stress during fish handling and transport. However, limited data are available on its physiological effects in common carp (Cyprinus carpio). The present study aimed to evaluate the anesthetic effects of quinaldine in common carp (Cyprinus carpio) fingerlings exposed to three concentrations of quinaldine viz; 20-mg/L, 40 mg/L, and 60 mg/L. Afterwards, the time required to attain deep anesthesia and full recovery were recorded. Blood and serum samples were collected at various intervals to assess haematological parameters including Haemoglobin (Hb), Total Leukocyte Count (TLC), Total Erythrocyte Count (TEC), Packed Cell Volume (PCV), Mean Corpuscular Haemoglobin (MCH), and Mean Corpuscular Haemoglobin Concentration (MCHC). Biochemical parameters such as total protein, albumin, globulin, glucose, and cortisol were also analysed. Furthermore, superoxide dismutase (SOD) and catalase enzyme (CAT) activities were assessed at different time points. The findings showed that fish exposed to 60 mg/L exhibited rapid induction and prolonged recovery, whereas 20 mg/L resulted in slower induction but faster recovery. Haematological indices reflected a decrease in total Hb, TEC, PCV, MCH, and MCHC, particularly at 60 mg/L of quinaldine. Biochemical parameters showed an increasing trend at higher concentration of quinaldine, notably at 40 mg/L and 60 mg/L. Additionally, SOD and CAT activity of liver and gill showed an increasing trend at higher concentrations. Scanning electron microscopy of gill tissues revealed mucus cell proliferation, sloughed epithelium, and irregular epithelial surfaces at higher doses. Together, these findings suggest that 20 mg/L of quinaldine has a mild and acceptable effect on the gill structure and physiological status of common carp. The findings of this study highlight that 20 mg/L of quinaldine is likely the safe concentration of this anesthetic drug in common carp.