Anesthesia of rainbow trout with citronellal: Efficacy and biochemical effects

The aim of this study was to assess the anesthetic efficacy and biochemical effects of citronellal on rainbow trout, Oncorhynchus mykiss. The fish were exposed to 200-800 µl/L citronellal to find the anesthesia induction and recovery times. The deep anesthesia stage was reached within 117-613 s, using 800-200 µl/L citronellal, respectively, and all fish recovered within 240-420 s. To assess biochemical responses, the fish were exposed to 200, 400, 600, and 800 µl/L of citronellal and blood-sampled after deep anesthesia. The results showed that anesthesia led to significant elevations in blood erythrocytes, hematocrit, hemoglobin, mean corpuscular volume, plasma lactate, and lactate dehydrogenase; these parameters exhibited increasing trends as citronellal concentration increased. These results along with significantly higher plasma lysozyme activity, cortisol, and glucose levels in 200 µl/L treatment suggest that an increase in citronellal concentration significantly mitigates hypoxia/stress responses in the fish. Significant elevations in plasma alkaline phosphatase activity and malondialdehyde level were observed in the 200 µl/L treatment, which suggests induction of hemolysis and oxidative stress in this treatment. There was a tendency to higher ammonia levels along with the increase in citronellal concentration, which might be due to early ammonia accumulation because of lower opercular movement in the fish. Except for blood hematocrit and mean corpuscular volume, there were no significant differences between the 600 and 800 µl/L citronellal treatments. In conclusion, high concentrations of citronellal are more suitable for trout anesthesia and blood sampling than low concentrations. Based on the present study, 600-800 µl/L citronellal is recommended for trout anesthesia.