The use of clove oil, metomidate, tricaine methanesulphonate and 2-phenoxyethanol for inducing anaesthesia and their effect on the cortisol stress response in black sea bass (Centropristis striata L.)

Juvenile and adult black sea bass (Centropristis striata L.) were exposed to various concentrations of four anaesthetics to determine practical dosages for handling as well as for procedures such as bleeding, ovarian biopsy or tag implantation. In experiment 1, juveniles exposed to either 2.0 mg L^?1 metomidate, 15 mg L^?1 clove oil, 70 mg L^?1 tricaine methanesulphonate (TMS) or 200 mg L^?1 2‐phenoxyethanol (2‐PE) reached stage II of anaesthesia in 3–5 min and could be handled for weighing and measuring. All fish had completed recovery to stage III within 6 min. In experiment 2, the established concentrations of each anaesthetic were tested on juveniles to determine their ability to prevent a reflex to a subcutaneous needle puncture. All of the fish exposed to clove oil (20 mg L^?1) and 40% of the TMS‐treated (70 mg L^?1) fish reacted while none of the fish anaesthetized in metomidate (2.0 mg L^?1) or 2‐PE (200 mg L^?1) responded to the needle puncture. In experiment 3, metomidate (5.0 mg L^?1), clove oil (30 mg L^?1) TMS (125 mg L^?1) or 2‐PE (300 mg L^?1) were all effective for performing an ovarian biopsy or tag implantation on adults. In experiment 4, TMS (125 mg L^?1) exacerbated the cortisol response to a short handling stressor during a 30 min exposure. Fish anaesthetized in 2‐PE (300 mg L^?1), metomidate (5.0 mg L^?1) or clove oil (40 mg L^?1) had increased cortisol levels associated with the handling stressor but there were no further increases during the remainder of the experimental period. The results demonstrate that these anaesthetics are effective for sedation and anaesthesia of black sea bass and that the best choice is dependant upon the procedures to be performed.     

Effects of clove oil and MS-222 on blood hormone profiles in rainbow trout Oncorhynchus mykiss, Walbaum

Clove oil has been demonstrated to be an effective, inexpensive anaesthetic and euthanizing agent for a number of fish species, including rainbow trout, used in aquaculture and fisheries research. However, the potential for clove oil to cause perturbations in important plasma hormone concentrations has not been investigated. The effect of anaesthesia and euthanasia in trout with eugenol (the active ingredient in clove oil) on plasma cortisol, glucose, growth hormone (GH) and two thyroid hormones [tri‐iodothyronine (T₃) and thyroxine (T₄)] was compared with tricaine methanesulfonate (MS‐222) anaesthesia, and stunning by cranial concussion in two experiments. Effects on blood chemistry were different when comparing the particular anaesthetic method being used. Stunning fish significantly increased plasma cortisol and glucose levels (both P<0.05), while euthanizing fish using either clove oil or MS‐222 had no effect on these hormone levels. In contrast, the levels of GH, T₃ and T₄ hormones were unaffected regardless of whether fish were euthanized by stunning, MS‐222 or clove oil. Variation in effects between hormones were observed using clove oil eugenol. In fish sampled 10 min after anaesthetizing with 150 mg L^?1 of eugenol, cortisol levels were significantly decreased (P<0.03), while there were no differences in either glucose or GH levels. Tri‐iodothyronine and T₄ also showed significantly elevated levels (P<0.05) after 10‐min exposure to eugenol. These results highlight the importance of investigating the potential effects of any new anaesthetic or euthanizing compounds on blood plasma parameters, prior to using them in a research setting, or when comparing results to other studies which have utilized alternative anaesthetic compounds.     

Anaesthetic efficacy of clove oil,benzocaine, 2‐phenoxyethanol and tricaine methanesulfonate in juvenile marbled spinefoot (Siganus rivulatus)

Anaesthetics are used in aquaculture and fisheries to facilitate routine procedures, such as capture, handling, transportation, tagging, grading and measurements that can often cause injury or induce physiological stress. Two experiments were performed to assess the efficacies of four anaesthetic agents, clove oil, benzocaine, 2‐phenoxyethanol and MS‐222 on juvenile marbled spinefoot rabbitfish (Siganus rivulatus). In the first experiment we tested the lowest effective doses that produced induction and recovery times in 3 min or less and 5 min or less respectively. Dosages were 70 mg L^?1 for clove oil, 60–70 mg L^?1 for benzocaine, 400 μL L^?1 for 2‐phenoxyethanol and 100–125 mg L^?1 for MS‐222. In the second experiment, we determined optimal concentrations of the four anaesthetics if they were to be used to transport rabbitfish fry. Anaesthetic concentrations suitable for handling and transport were: 10–15 mg L^?1 of MS‐222, 5–10 mg L^?1 of benzocaine, 5 mg L^?1 of clove oil and 50–100 μL L^?1 of 2‐phenoxyethanol. All anaesthetic agents are acceptable for use on S. rivulatus, however, 2‐phenoxyethanol, MS‐222 and clove oil appear to be more suitable than benzocaine. Further studies need to be conducted on effects of high and low doses of anaesthetic agents on physiology of marbled spinefoot.     

Comparison of the effects of four anaesthetics on biochemical blood profiles of perch

This study investigated the feasibility of using clove oil, 2-phenoxyethanol, or Propiscin as an alternative to tricaine methane sulphonate (MS 222) as a fish anaesthetic, particularly in regard to reducing fish stress. The biochemical blood profiles of perch Perca fluviatilis L. anaesthetized with either MS 222 (100 mg L⁻¹), clove oil (33 mg L⁻¹), 2-phenoxyethanol (0.40 mL L⁻¹) or Propiscin (1.0 mL L⁻¹), and a non-anaesthetized control group were compared. Biochemical profiles were determined from blood samples collected before treatment in controls. For each anaesthetic tested, fish were divided into two groups, one sampled immediately after 10-min anaesthesia and a second, sampled 24 h after 10-min anaesthesia. The values determined in the present study suggested that internal organs and tissues of perch were slightly altered by MS 222, clove oil and 2-phenoxyethanol anaesthesia, but not by Propiscin anaesthesia.     

Efficacy and effects of clove oil and MS‐222 on the immune‐biochemical responses of juvenile rohu Labeo rohita

The present study determined the effective concentrations of clove oil and MS‐222 in juvenile rohu Labeo rohita for quick induction and recovery. The immune‐biochemical responses due to 0, 1 and 24 hr exposure to those anaesthetics were also evaluated. Of four concentrations of the anaesthetics examined, the lowest effective concentration of clove oil and MS‐222 were 50 µl/L and 125 mg/L respectively. Clove oil and MS‐222 significantly increased the myeloperoxidase, total protein and alkaline phosphatase activity at some of the holding durations. However, superoxide anion production (after 0 and 1 hr) and antiprotease activity (after 24 hr) were significantly reduced in fish exposed to clove oil. Serum glucose content was significantly elevated in the MS‐222‐treated group. Furthermore, the clove oil‐treated group showed significantly higher levels of serum Na⁺ and K⁺, while the aspartate and alanine aminotransferase activities were significantly enhanced in the MS‐222 group. The use of both clove oil and MS‐222 is advised as an anaesthetic agent for rohu with a bias towards clove oil, considering its economic and operational feasibility.     

Effects of repeated handling, with or without anaesthesia, on feed intake and growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum)

The effects of weekly anaesthetization with clove oil and tricaine methanesulphonate (MS‐222) on feed intake and growth were examined in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually. Repeated handling without anaesthetics significantly reduced feed intake and weight gain compared with an unhandled control group during an 8‐week experiment. When anaesthetics were used during handling the feed consumption and weight gain were significantly (MS‐222) or not significantly (clove oil) higher than in fish handled without anaesthesia. When compared with the unhandled control group, neither of these two anaesthetics had significant effects on feed intake but, in contrast to MS‐222, repeated anaesthesia with clove oil had a significant negative effect on growth. However, the effects of MS‐222 and clove oil on the growth were not significantly different from each other. Feed conversion ratio (feed/gain) of MS‐222‐anaesthetized fish was significantly higher compared with unhandled control and handled control fish but was not significantly different from fish anaesthetized with clove oil. These results suggest that both MS‐222 and clove oil alleviate handling stress in juvenile rainbow trout, and that these two anaesthetics are rather similar with respect to their effects during repeated exposures.     

Comparison of tricaine methanesulphonate (MS222) and clove oil anaesthesia effects on the physiology of juvenile chinook salmon Oncorhynchus tshawytscha (Walbaum)

This study investigated the feasibility of using clove oil as an alternative to tricaine methanesulphonate as a fish anaesthetic, particularly in fish stress research. The physiological stress responses of juvenile chinook salmon Oncorhynchus tshawytscha (Walbaum) anaesthetized with either tricaine (50 mg L^?1) or clove oil (20 p.p.m.) were compared using unanaesthetized fish as controls. Haematocrit, serum cortisol and serum glucose concentrations, serum lysozyme activity and differential leucocyte counts were measured from blood samples collected before, during and upon recovery from anaesthesia and at specified intervals up to 72 h after recovery. Differences between the two anaesthetic groups were not significant for most of the physiological traits measured. Serum lysozyme activity of control fish, however, was significantly suppressed relative to the treated fish for 72 h after stress. Clove oil may be a safe and cost‐effective alternative to tricaine without significantly affecting study results. Furthermore, clove oil may be more practical for field‐based research, because a withdrawal period is unnecessary, and clove oil does not pose an environmental hazard.     

Effects of water temperature and body weight on anaesthetic efficiency in marbled rabbitfish (Siganus rivulatus)

The effects of four anaesthetic agents, tricaine methanesulphonate (MS‐222) (112.5 mg L^?1), 2‐phenoxyethanol (400 μL L^?1), clove oil (70 mg L^?1) and benzocaine (65 mg L^?1) on juvenile marbled spinefoot (Siganus rivulatus) of three mean body weights (7.3 g, 19.1 g, 55.5 g) and at three temperatures (20, 25, 30°C) were evaluated. In addition, the relationship between body lipid content and efficacy of the four anaesthetic agents was evaluated in juvenile S. rivulatus. Times necessary for induction and recovery were recorded. Significant effects of temperature on induction and recovery times were observed. Induction and recovery times decreased with increasing water temperature. No uniform relationship between body weight of juvenile marbled spinefoot and anaesthetic efficacy was observed. Body fat content was positively correlated with induction time only when MS‐222 was used but did not affect induction times of fish exposed to 2‐phenoxyethanol, clove oil or benzocaine. Recovery times were generally longer for all fish containing more body fat. Results of the study show that anaesthetic efficiency increases with increasing water temperature but is not strongly affected by body weight for juvenile marbled spinefoot. In addition, body fat in fish affected the efficacy of the various anaesthetic agents tested in this study, generally slowing down recovery.     

Essential oil of Aloysia triphylla in Nile tilapia: anaesthesia,stress parameters and sensory evaluation of fillets

The optimum concentration of anaesthetic used to facilitate fish handling can be determined based on induction and recovery time, among other factors. This study aimed to evaluate the effectiveness of the essential oil of Aloysia triphylla (EOAT) as an anaesthetic in the handling of Nile tilapia juveniles. Nile tilapias exemplars were immersed at 0 (control group), 10, 20, 30, 40, 80, 150, 300 and 450 μL L^?1 EOAT to evaluate sedation, anaesthesia and recovery time. The stress response was evaluated by the determination of plasma glucose, cortisol, lactate and paraoxonase levels in anaesthetized (300 μL L^?1 EOAT) and non‐anaesthetized fish. Fillets from both groups were evaluated for organoleptic characteristics (taste and odour). Concentrations of 80–450 μL L^?1 EOAT were effective in inducing anaesthesia. There was a significant reduction in plasma cortisol levels one hour after handling in individuals anaesthetized with 300 μL L^?1 EOAT compared to the control group. Tasters did not detect differences in fillet taste and odour between fish exposed and not exposed to EOAT. A concentration of 300 μL L^?1 EOAT is recommended for handling Nile tilapia because it presents good anaesthetic induction and recovery times, causes a reduction in plasma cortisol levels one hour after handling and does not affect the taste or odour of the fillets.     

Silver catfish Rhamdia quelen immersion anaesthesia with essential oil of Aloysia triphylla (L'Hérit) Britton or tricaine methanesulfonate: effect on stress response and antioxidant status

Responses to anaesthesia with essential oil (EO) of Aloysia triphylla (135 and 180 mg L^?1) and tricaine methanesulfonate (MS222) (150 and 300 mg L^?1) were assessed in silver catfish. Exposure to the anaesthetics elicited a stress response in the species. In the case of MS222, it was displayed as a release of cortisol into bloodstream, elevation in hematocrit and plasma ion loss. The EO presented cortisol‐blocking properties, but increased haematocrit and disturbances of hydromineral balance were observed. Liver antioxidant/oxidant status of EO and MS222‐anaesthetized silver catfish was also estimated. The synthetic anaesthetic induced lipoperoxidation, notwithstanding increased catalase contents, whereas the naturally occurring product was capable of preventing the formation of lipid peroxides, possibly due to combined actions of catalase and glutathione‐S‐transferase. Anaesthetic efficacy was also tested via induction and recovery times. Overall, the promising results obtained for the physiological parameters of the EO‐treated fish counterbalanced the slight prolonged induction time observed for 180 mg L^?1. As for 135 mg L^?1, both induction and recovery times were lengthy; despite that, the EO was able to promote oxidative protection and mitigate stress. None of the MS222 concentrations prompted such responses concomitantly.     

Effects of anaesthesia with MS-222, clove oil and CO2 on feed intake and plasma cortisol in steelhead trout (Oncorhynchus mykiss)

We examined the effects tricaine methanesulfonate (MS-222), clove oil and CO₂ on feed intake and cortisol response in steelhead trout, Oncorhynchus mykiss. Even though a body of literature exists about the effects of different anaesthetics on fish, no comparative information seems to be available about their effects on feed intake after anaesthesia, which would be important to know especially in aquaculture research. We anaesthetised juvenile steelhead trout with these three anaesthetics, and then sampled them 4, 24 and 48 h later. Fish in all groups ate relatively well already 4 h after anaesthesia. However, feed intake in fish treated with clove oil or MS-222 was lower than in the controls. There were no differences in feed intake among anaesthetised groups. Plasma cortisol concentrations were elevated 48 h after anaesthetisation, but the treatment means were equal throughout the experiment. Our results support previous findings that clove oil is a reasonable alternative to MS-222.     

Anaesthetic efficacy of MS‐222 and AQUI‐S® in advanced size fry of rohu,Labeo rohita, (Hamilton‐Buchanan)

Anaesthetic agents are very useful for reducing the stress caused by handling, sorting, transportation, artificial reproduction, tagging, administration of vaccines and surgical procedures in fish. The efficacy of two anaesthetics: MS‐222 and AQUI‐S^® were tested on rohu, Labeo rohita advanced size fry. The lowest effective doses that produced induction in 3 min or less and recovery times 5 min or less and meet the most criteria of good anaesthetic characteristics were 125 mg L^?1 of MS‐222, and 30 mg L^?1 of AQUI‐S^® in rohu, Labeo rohita advanced size fry. Induction times were significantly decreased with increased in the concentrations of any of the two tested anaesthetic agents. The lowest doses suitable for transportation of rohu advanced size fry observed were: 10–15 mg L^?1 of MS‐222 and 2.5 mg L^?1 AQUI‐S^®. Both anaesthetics showed promising to be used as anaesthetics for handling and transportation in rohu (Labeo rohita) advanced fry.     

The efficacy of MS‐222 as anaesthetic agent in four freshwater aquarium fish species

The efficacy of anaesthetic tricaine methanesulfonate (MS‐222) was evaluated in four freshwater aquarium fish species, Zebrafish (Danio rerio), Guppy (Poecilia reticulata), Discu (Symphysodon discus) and Green swordtail (Xiphophorus helleri). The correct dose of anaesthetic should induce the plane 4 of anaesthesia in less than 180 s, recovery in less than 300 s and must survive when exposed during 30 min to anaesthetic. Fishes were exposed to six concentrations of anaesthetic (75, 100, 125, 150, 200 and 250 mg L^?1) and the time of fish reaching plane 4 of anaesthesia, post exposure recovery, and the percentage of survival when fish were subject to 30 min in the anaesthetic were recorded. The optimal doses varied according to the species: D. rerio – 75, 100 and 125 mg L^?1, P. reticulata – 125, 150 and 200 mg L^?1, S. discus – 75 and 100 mg L^?1 and X. helleri – 125 and 150 mg L^?1. The induction time generally decreased significantly with increasing concentration of MS‐222 for all of the species evaluated. The recovery time had a tendency to increase with the increase of the MS‐222 concentration for D. rerio, P. reticulata and S. discus. On the other hand, X. helleri recovery time decreased with the increase of MS‐222 concentration. MS‐222 proved to be effective in anaesthesia for all the freshwater ornamental species studied. The main results clearly show that the optimal dose to anesthetize is fish species dependent and it is completely wrong to extrapolate optimal anaesthetic concentrations between different species.     

Eugenol as an efficacious anaesthetic for tambaqui, Colossoma macropomum (Cuvier)

Anaesthetics are important in fish culture to reduce handling stress and mortality. Eugenol is a promising anaesthetic because of its low cost, efficacy, safety margin for fish and lack of toxicity to humans. The goal of this study was to establish a protocol using eugenol as a fish anaesthetic for tambaqui Colossoma macropomum (Cuvier), and provide information for regulating authorities on establishing safety dosage protocols for its use. Juvenile and sub‐adult tambaqui were first individually exposed to doses of 35, 50, 65, 85, 100 or 135 mg L^?1 eugenol for 10 min. A second experiment examined the effect of the duration of exposure to eugenol on the time required for recovery and survival of tambaqui. A eugenol dose of 65 mg L^?1 was adequate to induce fish of both sizes into a surgical anaesthetic state, and recovery time was similar for dosages up to 100 mg L^?1. Exposure to the ideal dose (65 mg L^?1) for up to 30 min did not cause fish mortality. Fish blood glucose values were similar for all the tested eugenol doses as well as with the benzocaine control. The results show that eugenol is an efficient and safe anaesthetic for tambaqui.     

Use of MS‐222 (tricaine methanesulfonate) and propofol (2,6‐diisopropylphenol) as anaesthetics for the tetra Astyanax altiparanae (Teleostei,Characidae)

The aim of this study was to evaluate the anaesthetic effect of MS‐222 and propofol and determine their optimal concentrations for safe handling of the tetra Astyanax altiparanae in the laboratory. The fish were separated by length into three classes: I (1.5–5.0 cm), II (5.1–8.0 cm) and III (greater than 8.1 cm). Pilot tests were performed to evaluate the appropriate anaesthetic concentrations for inducing the five possible anaesthetic stages: I – sedation; II – light anaesthesia; III – deep anaesthesia; IV – surgical anaesthesia; and V – spinal collapse. After defining the maximum and minimum concentrations required to induce stage IV anaesthesia, the animals were exposed to five intermediate concentrations (n = 10 fish/concentration) of each anaesthetic for 15 min. The animals were then transferred to clean water to evaluate the time required for recovery. In addition, blood glucose levels were measured for class II and class III fish subjected to the previously defined ideal concentrations for each of the tested anaesthetics (n = 10 fish/treatment). Both evaluated substances are suitable to anaesthetize A. altiparanae. The optimal MS‐222 concentration was 90 mg L^?1, and this result was similar for all three size classes. The optimal propofol concentrations for inducing surgical anaesthesia in the size classes I, II and III were 0.22, 0.23 and 0.27 respectively.     

Anaesthesia of Atlantic halibut (Hippoglossus hippoglossus) Effect of pre‐anaesthetic sedation,and importance of body weight and water temperature

The efficacy of the anaesthetic agents benzocaine, metacaine (MS‐222), metomidate, 2‐phenoxyethanol, quinaldine and isoeugenol was studied in Atlantic halibut (Hippoglossus hippoglossus). Fish with an average body weight of 33 g were anaesthetized at 8 °C and fish with an average body weight of 1243 g were anaesthetized at 8 and 15 °C. Agents were tested individually and as combination anaesthesia comprising pre‐anaesthetic sedation, followed by anaesthesia. Induction and recovery times varied in relation to the body weight and water temperature. Large fish had longer induction times and shorter recovery times, and displayed reduced responsiveness to handling compared with small fish. A higher temperature resulted in shorter induction times, longer recovery times and increased responsiveness to handling. Lower dosages were used for all agents in combination anaesthesia. In small fish, this had no effect on the induction times but resulted in shorter recovery times and reduced responsiveness to handling. In large fish, combination anaesthesia resulted in shorter induction times whereas no uniform trend in recovery times and no differences in responsiveness to handling were observed. Neither individual agents nor combinations blocked all reflex reactions to external stimulation in all fish of any treatment group. MS‐222 and benzocaine, used separately or in combination anaesthesia, were the most effective agents in reducing reflex reactions.     

Comparative Efficacy of Anesthetics for the Freshwater Prawn Macrobrachiurn rosenbergii

Abstract— The freshwater prawn Macrobrachiurn rosenbergii is a commercially important culture species in the South Central United States. Two major constraints in the commercial culture of the freshwater prawn in the U.S. are poor survival during live transportation of seed‐stock to growout ponds, and live transportation of pond harvested prawn to distant live markets due to the territorial and cannibalistic nature of prawn. The use of anesthetics could possibly improve transport survival; however, to date anesthetic agents have not been evaluated for use with prawn. Two trials were conducted with juvenile freshwater prawn to compare the efficacy of anesthetics commonly used on fish. The first trial was designed to identify the most promising candidates. In Study 1, tricaine methanesulfonate (MS‐222), 2‐phenoxyethanol, quinaldine sulfate (quinaldine), clove oil, and Aqui‐S^TM were evaluated at 25 and 100 mg/L for 1 h in three replicate 10‐L glass containers, containing five juvenile prawn each. Relative sedation level was determined every 3 min for 1 h, then recovery time and survival were measured. In Study 1, MS‐222 and 2‐phenoxyethanol were determined to be ineffective on prawn at all rates tested. Based on their performance in Study 1, quinaldine, clove oil, and AquiS^TM were evaluated at 100, 200, and 300 mg/L in Study 2. Observations were determined as in Study 1. Clove oil and Aqui‐S^TM induced anesthesia faster and at lower concentrations than quinaldine. At the highest treatment rate (300 mg/L) prawn suffered 60% mortality in the Aqui‐S^TM treatment, 13% mortality in the quinaldine treatment, and 0% mortality in the clove oil treatment and control following a 1‐h exposure to these concentrations. Based on these data, Aqui‐S^TM and clove oil applied at 100 mg/L may be suitable anesthetic treatments for prawn. Additional research is needed to determine optimal time and dose relationships to minimize stress during holding, handling, and transportation of prawn.     

Minimally invasive evaluation of the anaesthetic efficacy of MS‐222 for ornamental discus fish using skin mucus biomarkers

Skin mucus has been demonstrated to provide stress biomarkers for evaluating the physiological status, providing new convenient and non‐invasive methods to detect stress response in fish. Here, we investigated the anaesthetic efficacy of tricaine methanesulphonate (MS‐222; 75–115 mg/L) for discus Symphysodon aequifasciata (34.27 ± 4.46 g; 8.10 ± 0.59 cm) using skin mucus stress biomarkers. The induction time, recovery time and respiratory frequency were also determined. According to the criteria for anaesthesia and recovery, discus fish to reach stage A3 (deep anaesthesia) within 3 min and to reach stage R4 (full recovery of normal behaviour) within 5 min were observed at 95–105 mg/L MS‐222. Respiratory frequency increased first and then decreased during MS‐222 exposure and increased after recovery. At 10 min after deep anaesthesia, a lower mucus glucose was only observed at 115 mg/L MS‐222. No change in mucus cortisol and increased lactate were observed in all treatments. Increased mucus protein was observed at 75, 85 and 95 mg/L MS‐222. At 10 min after recovery, increased mucus glucose and decreased mucus protein were observed at 85, 95 and 115 mg/L MS‐222, but increased mucus cortisol only at 115 mg/L and lactate only at 75 and 105 mg/L MS‐222. At 24 hr after recovery, mucus glucose returned to the initial level only at 75, 95 and 105 mg/L MS‐222, while cortisol at 75 and 85 mg/L and protein and lactate at 75 mg/L respectively. Overall, the effective dose of MS‐222 for discus fish has been suggested to be 95–105 mg/L.     

Physiological responses associated with capture and crowding stress in matrinxãBrycon cephalus (Gunther, 1869)

The dynamics of plasma cortisol, blood glucose, plasma chloride and liver glycogen were investigated in matrinxã (Brycon cephalus) submitted to capture and various periods of crowding. A total of 400 fish (700±22 g weight) were distributed in four ponds divided into four 50‐m² squares (25 fish/square, 350 g L^?1), where they were acclimated for 30 days. On the sampling day, after 24 h without food, all fish from three squares were transferred to the fourth square. Six fish were sampled before the procedure (control group, zero time) and 1, 3, 6 and 24 h after the capture and crowding. Each sampling was performed in a different pond to prevent additional stress. Fish were anaesthetized and blood and liver collected for biochemical analysis. Water temperature, pH, dissolved oxygen, alkalinity, ammonia and nitrite levels were within acceptable levels for matrinxã rearing. Slight but not significant increases were verified in plasma cortisol and blood glucose levels, as were decreases in plasma chloride and liver glycogen levels. The results suggest that matrinxã is highly tolerant to the procedures of capture and short‐term crowding.     

The anaesthetic effect of camphor (Cinnamomum camphora), clove (Syzygium aromaticum) and mint (Mentha arvensis) essential oils on clown anemonefish,Amphiprion ocellaris (Cuvier 1830)

The aim of this study was to evaluate the use of clove (Syzygium aromaticum), camphor (Cinnamomum camphora) and mint (Mentha arvensis) essential oils as anaesthetics during the management of clown anemonefish (Amphiprion ocellaris). For 15 min, the animals were subjected to concentrations of 5, 10, 20, 27 and 35 μL L^?1 of clove oil, 17, 35, 50, 70 and 100 μL L^?1 of mint oil, and 200, 400, 500, 550 and 600 μL L^?1 of camphor oil (tested in 10 animals per concentration). A control group (without anaesthetic) and a complementary group, which was exposed to ethanol, were also evaluated. After exposure to the anaesthetic, the fish were transferred to clean water to assess recovery. The mortality and feeding behaviour of the fish were then observed for 48 h after exposure to the oils. All of the essential oils produced an anaesthetic effect on A. ocellaris. The 27, 70 and 500 μL L^?1 concentrations of clove, mint, and camphor oils promoted surgical anaesthesia after 310.5, 312.0, and 535.0 s (medians) respectively. The recovery times of fish exposed to these same concentrations were 396, 329.5 and 229 s respectively. The decision of which oil to use is dependent on the management situation and the consideration of the induction and recovery times of each essential oil.