Abstract
This work evaluated the efficiency of clove oil as anaesthetic in handling and transportation of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). In the first experiment, safety concentrations of clove oil were assessed by measuring induction times to anaesthesia. The second experiment evaluated exposure times to anaesthetic. Clove oil efficiency during transportation was evaluated in a 24 h experiment using three concentrations of the anaesthetic (0, 9, and 18 mg.L-1). The most appropriate clove oil concentration to induce surgical anaesthesia was 90 mg.L-1. To biometry or other brief handling, the recommended concentration is 50-60 mg.L-1 as it provides fast recovery. Maximum anaesthesia time should be 10 min. The mortality rate of fish transported using 18 mg.L-1 of anaesthetic was significantly higher than that of the control group at 24 h of transportation and at 96 h after transportation. The fish transported using clove oil as anaesthetic presented more significant Na+ and K+ disorders as compared to the control group. As an anaesthetic, clove oil is efficient in the handling of Nile tilapia in routine fish hatchery procedures, although it should be avoided in the transportation.
Highlights
In Brazil, tilapia farming is usually carried out in two distinct sites: the hatchery station, where reproduction and sex reversion are conducted and juveniles grow up to 5 cm, and growing station, where the 5 cm fish reach harvest size
Clove oil is efficient in the handling of Nile tilapia in routine fish hatchery procedures, it should be avoided in the transportation
Clove oil has been extensively used in several fish species, and the results show that the substance is a good economic alternative to the chemicals normally used in fish anaesthesia
Summary
Ninety Nile tilapia juveniles (1.46 ± 0.38 g, 4.33 ± 0.30 cm) were obtained from a commercial supplier and transported to our research laboratory, where the individuals were acclimated in two 150 L tanks equipped with continuous water inflow and aeration. In the first experimental segment, six different clove oil concentrations were tested (50, 60, 70, 80, 90, and 100 mg.L-1). Recovery time was measured after the induction of anaesthesia at different exposure times with 90 mg.L-1 clove oil. The previously acclimated fish were individually exposed to the anaesthetic for 10, 20, and 30 min (n = 10 for each exposure time). Each fish was transferred to the recovery aquarium and the recovery time measured. The times to reach the different anaesthesia stages under the different clove oil concentrations, as well as the recovery times after exposure to the anaesthetic for different anaesthesia times were evaluated using an analysis of variance (ANOVA) followed by the Tukey test (p < 0.05) (ZAR 1999)
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