COMPARATIVE EFFICACY OF FOUR ANESTHETICS ON COMMON CARP CYPRINUS CARPIO

Anesthetics are often used to immobilise fishes in research. Many chemicals have been tested in anesthetisation of fishes and each chemical has its own merits and demerits. In the present study, four anesthetics namely, 2-phenoxyethanol, quinaldine, MS-222, and benzocaine were selected to test the efficiency in anesthetisation of common carp Cyprinus carpia. Results indicated that the induction time of the fish exposed in four anesthetic solutions significantly (P < 0.05) decreased with increasing concentration but recovery time was independent to concentration. The effective concentration which produced anesthesia within 3 minutes and allowed recovery within 5 minutes in common carp were 600 mm3/dm3 (2-phenoxyethanol), 6 mg/ dm3 {quinaldine), 50 mg/ dm3 (MS-222), and 50 mg/ dm3 (benzocaine). A brief comparison about the advantages and drawbacks of the four anesthetics are given in Tab. 4.


INTRODUCTION
Many chemicals are used as anesthetics in research to immobilise fishes and they are necessary to avoid stress caused by manipulation (Marking and Meyer 1985;Gilderhus and Marking 1987;Summerfelt and Smith 1990).Each anesthetic has its own merits and demerits with regard to cost, toxicity, efficacy, safety, manipulation, induction and recovery time.The aim of the present study was to determine the effective concentration of four anesthetics namely, 2-phenoxyethanol (ethylene gtycol monophenyl ether), quinaldine (2-methykminoline), , and benzocaine (ethyl arninobenzocate) in anesthetisation of common carp Cyprinus carpio.These anesthetics have been unverified automated demonstrated to be effective and have been widely used in many fish species (Marking and Meyer 1985;Gilderhus and Marking 1987).In this study, first effective concentration of each anesthetic was determined, then the applying cost of each anesthetic was calculated.
Finally a brief comparisons of their merits and demerits were presented in a form of table.

MATERIALS AND METHODS
Good genetic strains and healthy common carp of a single egg mass were purchased from Fish Farmer's Development Authority (FFDA), Tirunelveli, South India.These fish were acclimatised to laboratory conditions in a 1000-dm 3 cement tank (525 fish) on a laboratory prepared pelleted diet containing 38% crude protein, 7.5% crude lipid, and 33% crude carbohydrate for two weeks.The uniform sized (5.15 ±0.12 g live weight) fish were randomly stocked (25 fish/concentration) into 25 dm 3 glass aquarium filled with 20 dm 3 fresh water containing differeni concentration of anesthetic.The physicochemical characteristics of four anesthetics and their concentrations used in this study are illustrated in Tabs. 1 and 2, respectively.Since quinaldine and benzocaine are sparingly soluble in water, they were first dissolved in 95% ethanol at 1 g/10 cm 3 and 1 g/10 cm 3 , respectively.Crystalline MS-222 is readily soluble in water, so they were dissolved in water 1 g/10 cm 3 before adding to aquaria.Only 2-phenoxyethanol was added directly into the anesthetic tank.
Water temperature, oxygen content, pH and salinity during the acclimatisation and the experiment were about 27 to 29°C, 6 to 7 ppm, 7.3 to 7.8 and 0.5 to 0.7 ppt, respectively.
Table 1 Physicochemical characteristics of four anesthetics used in the study (Hseu et al.1998)The anesthetic induction time is the period from the time when the test fish is placed in the anesthetic tank until the time is stops swimming and its tail stops swinging ( Colourless oily liquid, molecular weight 165.2; melting point 88 to 90°C: barely soluble in water (0.4 g/dm 3 } but soluble in acetone and ethanol and Riple 1989).After the induction time the anesthetized fish were immediately transferred into a recovery tank.The recovery time is the period from the time when an anesthetized fish is placed in a recovery tank until it recovers from anesthetization with full equilibrium motion (Hseu et al. 1998).The effective concentration is defined as the minimum concentration required to anesthetize the fish within three minutes in the anesthetic tank and which allows recovery within five minutes in the recovery tank (Hseu et al. 1998).Data were analysed by one-way ANOVA followed by Tukey type multiple comparisons at five percent level of significant (Zar 1984).

RESULTS AND DISCUSSION
Generally, an ideal anesthetic should produce rapid anesthesia (within 3 or 5 minutes), a quick recovery, not be toxic to fish and users, leave low tissue residue and be inexpensive (Marking and Meyer 1985;Gilderhus and Marking 1987).Results of the present study showed that the induction time of common carp exposed to four anesthetic significantly (P <0.05) decreased within increasing their concentrations (Tab.2).The recovery time was generally within one minute and no mortality was observed during the experimental period.
Among all the four anesthetics, 2-phenoxyethanol was the most conveniently used and no preparation was necessary before treatment of fish.Guo et al. (1995) suggested that 2-phenoxyethanol was more suitable than either quinate of MS-222 to sedate non-food fishes (e.g.ornamental fishes) during live transport.A major drawback of 2-phenoxyethanol is comparatively high anesthetic doses in fishes.The effective anesthetic doses of 2-phenoxyethanol in most fishes ranged from 200 to 600 mm 3 /dm 3 (Tahashima et al. 1982; Gilderhus and Marking 1987; Mattson and Riple 1989: Hseu et al 1994, 1997, 1998; Hseu and   Ting 1995; Weyl et al. 1996).In the present study, the effective concentration of 2-phenoxyethanol for common carp was 600 mm 3 /dm 3 .
Like MS-222, quinaldine depressed the sensory centres of the central nervous system (Locke 1969).Due to its lipid solubility, quinaldine tends to accumulate in the brain (Brandenburger Brown et al. 1972).Atlantic mackerel required 4 to 6 mg/dm 3 to completely anesthetise at 12 to 17°C (Lambert 1982).Tilapia were extremely tolerant to quinaldine and 500 mg/dm 3 was required to completely anesthetise.The effective concentration of quinaldine for goldline sea bream was 9 mm 3 /dm 3 (Hseu et al. 1998).In the present study 6 mg/dm 3 quinaldine was required to anesthetise common carp and it was the lowest effective concentration among the four anesthetics.
In the present study, the effective concentration of MS-222 for common carp was 50 mg/dm 3 and this concentration was half of the effective dosage (100 mg/dm 3 ) of goldline sea bream (Hseu et al. 1998).Many authors suggested that MS-222 should be neutralised with alkali, such as NaOH thus, sea water could act as a buffer to prevent excessive acidification from MS-222 (Ohr 1976;Smit and Hattingh 1979).
Benzocaine has a similar chemical structure of MS-222 but unlike MS-222, it was barely soluble in water (Summerfett and Smith 1990), In some fish, benzocaine is more suitable than MS-222 because striped bass are very sensitive to MS-222 and benzocaine induced, anesthesia very rapidly than MS-222 in white perch.The effective concentrations of benzocaine for striped bass and goldline sea bream were 55-80 mg/dm 3 (Gilderhus et al. 1991) and 50 mg/dm 3 (Hseu et al. 1998), respectively.In the present study MS-222 also was as effective anesthetic for common carp and its effective concentration was 60 mg/dm 3 .
The cost of application of each anesthetic was calculated based on the effective concentration and the price of anesthetic (Tab.3).Among the four anesthetics, the cheapest one was quinaldine and the most expensive one was MS-222 followed by 2-phenoxyethanol.The cost of benzocaine was inexpensive.In general, the recovery time of 2-phenoxyethanol, quinaldine, MS-222, and benzocaine are not very long (Imamuia-Kojima et al. 1987;Allen 1988).Benzocaine and MS-222 are comparatively safety to users (Summerfelt and Smith 1990).Quinaldine is highly irritating the mucus membrane of eyes and respiratory system (Summerfert and Smith 1990).Morton (1990)suggested that the regular usage of 2-phenoxyethanol causes some neurophy sio logical syndrome to users (Tab.4)

Table 2
Induction time and recovery time of common carp exposed in different anesthetics for 10 minutes.MeaniSD (n =10); mean in the same column having the same superscript are not significantly different (P > 0.05)

Table 3
Costs of four anesthetics used with common carp (US $) Price of the maximum package size of each chemical In AldrichCatalog (1998-99)Brief comparison of four anesthetics used with fish *