Introduction
An essay was performed to assess the efficacy of clove oil as an anaesthetic for the commercial size of the doctor fish Garra rufa (Heckel, 1843). Several concentrations of clove oil were used to establish the minimum concentration producing desirable anaesthetic effects on this species. Despite the fact that G. rufa is a well known fish, little is known about its rearing and reproduction conditions. Still, there is a high demand for
G. rufa worldwide, not only for recreational purposes in aquariophilia, but mostly for therapeutic/cosmetic treatments related with skin problems. Therefore, it is necessary to study the better ways to handle these animals, without inflicting them anguish, suffering, pain and permanent damages, according to the welfare policies of Directive 2010/63/EC.
Materials and methods
Garra rufa, were purchased and reared in aquaria of 20 l. Each aquarium was equipped with an internal Venturi filtering system and strong aeration. Maintenance consisted on weekly water replacements and fish feeding 3 times per day ad libitum. Fish acclimation lasted 2 weeks. G. rufa, were distributed into groups of 10 fishes, with total length from 3.5 to 5.5 cm. They were subjected to 6 different concentrations of clove oil, from 30 to
130mg l-1, with an increment of 20mg l-1 each time.
The anaesthetic procedures were performed with water from the rearing systems (Ackerman et al., 2005), presenting the following environmental parameters: 20ºC, pH 7.4, NH4+<0.3mg l-1; NO3-<0.4mg l-1, N03-<16.8mg l-1. The fish fasted from the day prior to the trial (Treves-Brown, 2000). The clove oil was firstly dissolved in ethanol at 1:10 ratio. G. rufa were monitored from the moment when they were inserted in a recipient, with the anaesthetic solution and strong aeration. The anaesthesia induction time was measured until the fish laid quiet sideways, on the bottom, and ceased the opercular movements. Then, the fish and were removed, measured for total length, wet weighed and observed for 1.5min, checking for any possible movements. Next, G. rufa were inserted in a recipient with strong aeration and the recovery time was measured until they exhibed perfect buoyancy control and voluntary swimming activity. The daily dose of food was supplied to the fish afterwards (0.04gday-1fish-1) and their behaviour was monitored for 30min.
Results
There were no statistically significant differences between the fish total length, but those subjected to more than 90 mg.l-1 of clove oil were significantly heavier.
All the anaesthesia induction times obtained were statistically and significantly different. Concentrations 30 and 50 mg.l-1 were not effective to induce anaesthesia in less than 5min. The concentrations 70 mg.l-1 and130 mg.l-1 produced faster induction times for the thinner and fatter fish, respectively. It was only possible to maintain anaesthesia for 1.5min in concentrations above 90 mg.l-1, even though some fish were able to produce opercular movements and body contractions, while handling them during that time. In general terms, the anaesthesia recovery time was longer as the clove oil concentration increased, but rarely exceeded 5 minutes. No mortality or illness were observed during the procedures, or on the next following 15 days. The fish revealed appetence for food immediately after returning to their rearing systems, consuming the daily dose in less than 10 minutes.
Conclusion
The clove oil concentration 130 mg.l-1 proved to be the most suitable to handle
Garra rufa, as it produced faster anaesthesia induction, which held for 1.5 minutes and there were no undesirable consequences for the fish welfare. It showed similar anaesthesia induction times similar to those of other cyprinids, as the common carp (Hajek et al., 1997) and goldfish (Perdikaris et al., 1997), as well as salmonids like the rainbow trout (Anderson et al., 1997). For these reasons, a clove oil concentration 130 mg.l-1 is recommended to be used for this species, attending its commercial size (total length of 3.5 to 5.5 cm).
References
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