There are many agents used to anaesthetize fish. Obtaining supplies
of anaesthetics will depend on location - but all veterinarians should
be able to obtain MS222 for you. Some of these anaesthesia agents can be
obtained from the local pharmacy - or mail order from hobbyist
MS222 (tricaine methane
sulphonate) is the only product licensed for fish use. It is a white
water-soluble powder which is stable when kept cool and dry. It is
a derivative of benzocaine (see below) A standard stock solution is made
by adding 10g of tricaine to a litre of water - which should be stored
in a dark container as it is unstable in sunlight. MS222 solutions are
acidic and therefore the pH of the anaesthesia solution needs to be
checked prior to use. In poorly buffered water it may be necessary to
buffer the standard stock solution using sodium bicarbonate -
maintaining the pH between 7 - 7.5.
MS222 is an hypoxic agent- so therefore the anaesthesia vessel should
be vigorously aerated in use. Tricaine is used at a rate between 50 -
100mg / litre, which means adding 5-10 mls of standard stock solution to
each litre of water used. Fish would normally recover in ten minutes or
Benzocaine (ethyl aminobenzoate).
A colourless crystal or white powder that is a popular anaesthetic for
fish. It is cheaper than MS222. Benzocaine is poorly water-soluble
and needs to be prepared in either ethanol or acetone.
It has a reasonably wide margin of safety and doesn't require
buffering. Benzocaine is more toxic at warmer temperatures. The stock
solution should be kept in a dark container, and like tricaine it acts
as a hypoxic agent, so aeration is required when it is used.
A standard stock solution can be prepared by adding 100g of
benzocaine to one litre of acetone/ ethanol. This is then used at a rate
of 1ml per litre of water. At these levels the fish should lose
equilibrium in in 2-4 minutes. Fish should recover in ten minutes or
Eugenol or clove oil is often
available over the counter at many pharmacies. It is not completely
water soluble and should be mixed with ethanol or acetone at a standard
rate of 1:10 (i.e. 100ml eugenol to one litre of solvent) This gives a
working solution of 100mg of eugenol per ml of stock solution.
It is used at a rate of 40 -100mg per litre which equals 0.4 - 1.0 ml
of stock solution per litre of water.
Other anesthesia agents include: Quinaldine
Sulphate - light yellow crystalline powder, more expensive
than tricaine, water soluble and needs to be buffered as tricaine. Its
advantages are rapid induction and recovery. Reported to a gill
irritant. Although fish lose equilibrium, there is not a total loss of
cellosolve) used at a rate of 0.1 - 0.5 ml / litre. It has a narrow
margin of safety. Although cheaper than many anaesthetics it has adverse
side effects such as a long induction time and erratic swimming. It may
cause liver and kidney damage
There are several other agents used, but these are not readily
available. The other option available to hobbyists in some areas are
proprietary preparations. For example in the UK, NT Labs now market Koi