This study aims to investigate the use of clove oil as an anaesthetic agent for Heterobranchus bidorsalis juveniles and assess the effects on the test fish, using some hematological parameters. Different concentrations of clove oil (0.8 to 1.2 ppm) were used in static water to determine the induction time and recovery time of the test organisms. Behavioral changes of the test fish were observed, the time the fish became immobilized and recovery from anaesthesia was recorded. The results showed erratic swimming, loss of equilibrium, loss of body movement with continued operculum movements, and loss of reflex of the test organisms during the period of exposure at higher concentrations (1.0 to 1.2 ppm) of clove oil. The physiological stress responses of H. bidorsalis juveniles increase when compared with fish in the control experiment. The induction time (119 s) significantly decreased with increasing concentrations of clove oil (1.2 ppm), while the recovery times ranged between 180 to 906 s from lower concentration (0.8 ppm) of clove oil to the highest concentrations (1.2 ppm).There was a positive linear effect (R2=0.95, P<0.05) between the concentration of clove oil and the induction time. The values obtained from hematological responses of the test organisms exposed to different concentrations of clove oil showed that the clove oil caused a concentration dependent changes in the blood of H. bidorsalis juveniles with significant reduction (P<0.05) in the values of packed cell volume (PCV) (26.00 to 16.00), haemoglobin (Hb) (8.70 to 5.90), mean corpuscular volume (MCV) (130.00 to 70.70) and the values of mean corpuscular haemoglobin (MCH) (38.61 to 32.41), and white blood cell (WBC) (29.50 to 73.50) increased significantly (P<0.05) with increasing concentrations of clove oil, while the values of red blood cell (RBC) and mean cell haemoglobin concentration (MCHC) varies with no definite pattern. Clove oil could be used as anaesthetic agent in fisheries because the induction and recovery times were within the recommendation range used in fishery management and does not pose any environmental hazard.
Key words: Heterobranchus bidorsalis, clove oil, anaesthetic effect, haematology examination, induction time, recovery time.
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