And Anaesthetics For The Controlled Management Of Fresh Water Fishes
Scholar, Faculty of Science, Mahatma Gandhi University, Kerala,
686560, India. Correspondence: firstname.lastname@example.org
is a state caused by an applied external agent resulting in a loss of
sensation through depression of the nervous system.
The use of anesthetics in fisheries and aquaculture research greatly
facilitates in procedures including induction of breeding, handling
during stripping and transport of broodstock. Anesthesia and sedation
is usually essential to minimize stress and physical damage in
handling the fish for routine operations (Summerfelt and Smith, 1990;
1997; Ross et
the use of anesthetics is primarily for the purpose of holding fish
immobile while the animal is being handled for sampling, anesthetics
are also used to lower the level of stress associated with such
choosing an anesthetic a number of considerations are important such
as its efficacy, cost, availability, ease of use and side effects on
fish, humans and the environment (Marking and Meyer, 1985).
Overdosing of an anesthetic or retaining the fish in an anesthetic
bath for too long leads to the fading of ventilation, hypoxia, and
finally, respiratory and cardiac collapse (Tytler and Hawkins, 1981).
wide variety of compounds have been utilized to anesthetize fish
during artificial propagation techniques. The
use of anesthetics in fish has spanned more than the last five
decades and many chemicals (MS-222, benzocaine, quinaldine,
chlorobutanol, phenoxyethanol, metomidate etc.) have been employed in
fresh water fishes.
of anesthetization included induction, maintenance and recovery.
Induction of anesthesia
anaesthetization anaesthetic agents are inhaled through the gills and
rapidly enter the blood. From there they are transported to the
central nervous system and excreted via the gills upon the fish's
return to fresh water. They work by inducing a calming effect
followed by a successive loss of equilibrium, mobility,
consciousness, and reflex action. Respiratory and cardiac failure
follows overdose or exposure. The induction time is the period from
the time when an experimental fish is placed in the anesthetic tank
to the time it does not respond to external stimuli. The
lowest effective concentration is the concentration that produces
general anaesthesia (Stage IV of Anesthesia) within 3 min and allows
the recovery within 10 min (Gilderhus, 1990; Weyl et
stages achieved usually depend on the dose and the length of
the anaesthetic procedure fishes were netted from the holding tank
and placed in experimental tank mixed with the anesthetic solution.
When a fish become anaesthetized, it was immediately taken out and
then put into a recovery tank with fresh aerated water. Each fish was
used only once and then subjected to monitoring for any adverse
effect for another 24 hours. There is a considerable variation in the
response to anaesthetics which can result from individual metabolic
differences, temperatures and physical condition. By careful
observation you will minimized the possibility of an overdose. It is
important to observe the fish at all times and if necessary to
terminate the induction. It is important that anaesthetic and
recovery tanks were prepared ahead of time
anesthesia a number of guidelines were followed such as; Stopped
feeding 24-hour before the experiment, properly aerated anesthetic
baths, same temperature was maintained in bath as well as in holding
tanks and thoroughly aerated recovery bath. It
is critical to monitor water quality in order to reduce anesthetic
mortality; Assuming aeration, DO, pH, and temperature are
appropriate, the important one is ammonia concentrations.
of anaesthetization include induction, maintenance and recovery. A
maximum duration from initial anaesthetic exposure to induction
(stage IV) and the induction stage achieved usually depends on the
dose and the length of exposure. Generally, an ideal anaesthetic
should produce anesthesia rapidly (e.g., less than 3 or 5 min), allow
a speedy recovery, not be toxic to fish and users, leave low tissue
residues, and be inexpensive (Marking and Meyer, 1985; Gilderhus and
Marking, 1987). The anaesthetic induction time is the period from the
time when an experimental fish is placed in the anaesthetic tank
until the time it does not respond to external stimuli. The lowest
effective concentration is the concentration that produces general
anaesthesia within 3 min and allows the recovery within 10 min
(Gilderhus, 1990; Weyl et
of anesthesia and recovery (Iwama et
of gross body movements but with continued opercular movements
in Stage II with cessation of opercular movements
immobilized but opercular movements just starting
opercular movements and gross body movements beginning
regained and pre anaesthetic appearance
occurs when the fish is placed in anesthetic-free water after
induction process. In
most cases the fish will be treated near to the tank or pond and can
be returned to its home for recovery. If this is not the case a
well-aerated recovery tank should be prepared in advance. The
recovery time is the period from the time when an anesthetized fish
is placed in a recovery tank to the time it recovers from
anesthetization with full equilibrium motion.
Initial recovery took a few seconds to minutes, depending on the
concentration of anesthetic administered.
fish fully recover from inhalant anesthetics within 5 minutes;
recoveries extending more than 10 minutes indicate an excessive
anesthetic dosage or a compromised animal (Ross, 2001). As the fish
recovers, respiration increases, muscle tone returns, fin movements
resume and the fish swims progressively until it regains full
there is no sign of recovery within a minute or so, it will be
necessary to try and get water moving over the gill filaments.
Alternatively the fish can be held in the water stream which will
force oxygenated water over the gills. The
fish should be monitored for 24-hours for any adverse effects.
(MS-222), [3-aminobenzoic acidethyl ester methanesulfonate] is the
most widely used fish anesthetic, and it is extremely effective for
rapid induction of deep anesthesia.
It is sold as a powder which readily mixes with water. It may be
prudent to check the pH of the water after addition of MS-222 to
ascertain adequate buffering has been achieved. It
is a white crystalline powder that is easily dissolved in water, with
a solubility of 1.25 g/mL water, at 20 oC.
Dose is related to species, size and density of the fish, as well as
water temperature and hardness, but in general, anesthetic doses are
usually between 25 to 100 mg/L. TMS is also known as MS-222,
TM18Finquel, Tricaine, tricaine methanesulfonate and Metacaine.
[p-aminobenzoic acid ethyl ester] has two forms: a crystalline salt
with water solubility of 0.4 g/L, or a freebase fo The efficacy of
benzocaine has been shown to be affected by the size of the fish,
where the smallest fish require the lowest dose, as well as by the
temperature of the water (Gilderhus, 1989). Reported doses range from
25 B 100 mg/L with doses for salmonids falling in the range between
25 B 45 mg/L (Gilderhus, 1989). Benzocaine must be dissolved in ethyl
alcohol first at 0.2 g/mL. Benzocaine is also known as TM1Anesthesin,
TM14Anesthone, TM2Americaine, ethyl aminobenzoate, Orthesin and
(2-PE) [1-hydroxy-2-phenoxyethane] is a colourless, oily, aromatic
liquid with a burning taste, and has solubility in water of 27 g/L at
(Merck and Company, 1989). The efficacy of 2-PE varies with the size
of the fish and with the temperature of the water (Sehdev et
1963). While the effective dosage for salmonids is in the range of
200 B 300 μL/L, the lethal dose is as low as 500 μL/L, which leaves
little margin for safety. 2-phenoxyethanol is also known by the names
phenyl cellosolve, phenoxethol, phenoxetol, ethylene glycol
monophenyl ether, and beta-hydroxyethyl phenyl ether.
may be dissolved in water by injecting the solution through a fine
gauge needle underwater and mixing. Isoflurane is utilized for human
anesthesia in a vaporized form. It is very safe and has been utilized
for extensive surgical procedures in koi. It is a controlled
substance and expensive. While safe and effective, more economical
alternatives are available to immobilize koi for venipuncture
oil, as commonly sold, varies from lot to lot in the strength and
composition of its components. The major active ingredients are
85-95% eugenol with the balance isoeugenol and methyleugenol. It is
inexpensive and readily available without a prescription. A starting
dose might be 0.5 ml per gallon of water. As clove oil does not mix
readily with water, steps must be taken to ensure the oil is evenly
mixed with the water in the anesthesia water. Some put a measured
amount of clove oil in a vinyl bag, add water and shake vigorously.
This is then mixed with the rest of the water in the anesthesia tub.
Another approach is to mix the clove oil with ethanol then add it to
the water in the anesthesia container.
[propyl-DL-1-(phenylethyl) imidazole-5-carboxylate hydrochloride] is
a crystalline powder which resembles metomidate and etomidate
structurally, and is freely soluble in both fresh water and salt
water. It is stable in solution for long periods and is 100 times
more soluble than TMS (Thienpont & Niemegeers, 1965). Propoxate
is 10 times more potent than TMS. Effective concentrations range from
0.5 mg/L to 10 mg/L (Summerfelt & Smith, 1990). A level of 0.25
mg/L is safe for anesthesia of lengths up to 16 hours. Ross &
Ross (1984) recommend a dose of between 1 and 4 mg/L to anaesthetize
fish resulting in induction times ranging from 30 seconds for higher
[1-(1-phenylethyl)-1H-imidazole-5-carboxylic acid methyl ester] is a
watersoluble powder which has the properties of a hypnotic, or
sleep-inducing, drug. Etomidate
[1-(1-phenylethyl)-1H-imidazole-5-carboxylic acid ethyl ester] is a
colourless, odourless crystalline analogue of metomidate and
propoxate (Merck and Company, 1989). It has been used on humans as a
hypnotic drug, but it is very expensive and difficult to obtain
(Bell, 1987). Efficient dosages range from 1 B 10 mg/L (Olsen et
[2-(diethylamino)-N-(2,6-dimethylphenyl) acetimide], in freebase
form, is insoluble in water, but freely soluble in acetone or
alcohol. It is generally used in the hydrochloride salt form which is
freely soluble in water (Merck and Company, 1989). Lidocaine has been
used in combination with sodium bicarbonate to anaesthetize carp
and catfish (Ictalurus
The addition of sodium bicarbonate, at 1 g/L, has been demonstrated
to enhance the anaesthetic effects of lidocaine. Without the addition
of bicarbonate, there are huge variations in required doses. For
example, tilapia required in excess of 800% more lidocaine than carp
when it was administered in the absence of sodium bicarbonate.
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