Abstract
The present study was carried out to evaluate the potential of the aqueous leaf and freeze-dried leaf extracts of Tephrosia vogelii as tranquilizers on an African catfish, Hetetobranchus longifilis post juveniles (mean weight 115.00±25.00g) obtained from wild stock. They were acclimatized under laboratory conditions for two weeks prior to the commencement of the experiment. The fish were fed once a day at 9.00 hours at 4% body weight during the period of acclimatization. Each tank containing acclimatization water was aerated to enhance dissolved oxygen, and water was changed daily to prevent metabolic waste build up. Experimental fish were starved for 24 hours prior to sedation to prevent regurgitation from the gastro-intestinal tract (GIT). Four healthy Hetetobranchus longifilis were selected randomly from both the control and treatment groups. Each fish was weighted and injected 0.05ml of aqueous and freeze-dried leaf extracts at concentrations of 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06g/l using №. 23 needle and a 2ml heparinized syringe. Injection was done intramuscularly (IM) at the dorsal saddle just above the lateral line behind the operculum. Fish in the control group were injected with distilled water. Injected fish were observed for behavioural responses. The result showed that H. longifilis injected with the freeze-dried leaf extract of T. vogelii passed sequentially through the first three stages of anaesthesia but could not attain total loss of equilibrium (stage 4 of anaesthsia). Behavioural responses included mucus secretion, slow and erratic swimming, excrement discharge, increase in opercular beat rate, strong retension of reflex action, partial loss of equilibrium and colour change. The induction time decreased with increasing concentration of the anaesthetic extract. The recovery time followed the reverse order. The opercular beat rates, before and after sedation in the treatment groups showed increase over that in the control group and it increased with increasing concentration. The result of the experiment with aqueous leaf extract showed that there was no significant difference in opercular beat rate after sedation in all centrations used (P>0.05). The result also showed that at higher concentration (0.06g/l) induction was time 44.67 seconds while at concentration 0.02g/l induction time was 83.70 seconds. In the case of the freeze-dried leaf extract of T. vogelii the induction at concentration 0.06g/l was 49.33 seconds while at concentration 0.02g/l induction time 76.67 seconds.
Highlights
Chemical anaesthetics are widely used for fish anaesthtics
Inspite of the growing number of chemical anaesthetics used in aquaculture, only MS-222 has been approved for use with food fish in the USA by the Food and Drug Administration (FDA) and in the European
The objective of the present study is to investigate the possible use of T. vogelii as a tranquilizer for fish and to compare the effect of the aqueous leaf and freeze dried leaf extracts on H. longifilis
Summary
Inspite of the growing number of chemical anaesthetics used in aquaculture, only MS-222 has been approved for use with food fish in the USA by the Food and Drug Administration (FDA) and in the European. Union (EU) [40, 8] This approval of MS-222 for use on edible fish notwithstanding, fish treated with MS-222 must be held for 21 days as required by law in those countries before human consumption. The restriction of several chemical anaesthetics for use with food fish is because they are not biodegradable, have negative environmental impact and health risks on both the fish and the handler. Inadequacy of chemical anaesthetic has resulted in a renewed interest to develope green (plant–derived) anaesthetics with low environmental impact and health risks [33]. With the advent of modernization many communities are no longer involved in fishing so the plant is becoming extinct
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