(for the US readers that's Fish anesthesia with Aqua-Sed)
Before you anaesthetise a fish check it out first, so that you can plan.
- Fish should be viewed in the water (from above and from the side if possible), assessing their movements and respiratory rate. In general, fish movements are fluid and seeming relatively effortless. The respiratory movements are generally slow and not obvious. ‘Wooden’ movements, or marked respiratory movements should be viewed with suspicion.
- The skin in general should be smooth and unbroken, haemorrhages may suggest localised scale damage or more serious septicaemic problems.
- The scales should normally lay flat against the body. Lifting of scales to produce a ‘pine-cone’ effect may be due to localised or generalised fluid build up in the skin or due to abdominal swelling due to ascites (fluid in the belly of the fish).
- During the overall assessment of the condition of the fish including observation of its respiratory action, gills may be glimpsed partially. In the majority of cases it will be necessary to lightly anaesthetise fish to examine the gills in detail. The gill can be seen by gently lifting the operculum and perhaps using a suitable light source to illuminate the buccal cavity. The gills should normally be a healthy ‘salmon pink’ colour, with clearly demarcated primary lamellae.
Anaesthetising fish is fairly easy BUT still isn’t something to be done lightly. Any anaesthetic a carries a risk, sometimes because the animal has an unknown/undiagnosed problem which causes a problem. For this reason we aren’t keen on the common practice of routine anaesthesia of koi carp ‘just to check them out’. That said, there are lots of good reasons eg.
- handling of - valuable fish, dangerous fish, particularly large fish
- handling broodstock for stripping, blood sampling, treatment etc
- vaccination by injection
The needs of these various tasks are different so care must be taken with all applications. The transition between stages of anaesthesia can be very rapid so great care is needed.
The individual response of a fish to an anaesthetic and its transition between the various stages is dependent on a number of factors.
- Gill area to body weight ratio is particularly important,
- Size and weight: metabolic rate,
- Fat (lipid) content which varies with season of the year,
- Sex, maturity, diet, condition, disease
Stages of anaesthesia
stage 1 Light sedation slight loss of reactivity
stage 2 Deep sedation total loss of reactivity except to
strong pressure, equilibrium normal
stage 3 Partial loss of erratic swimming, increased gill movements
stage 4 Total loss of reactivity only to deep pressure stimuli
stage 5 Loss of reflex total loss of reactivity, very shallow
activity opercular movements
stage 6 Medullary gasping followed by gill movements stopping
GOLDEN RULES FOR ANAESTHESIA
- Don’t try to hurry the process, especially with a species that you haven’t anaesthetised before
- Plan it properly
- Anaesthetised fish must be watched throughout the procedure
- Don’t take them deeper than necessary, inevitably the level of anaesthesia will deepen a little when the fish is removed from anaesthetic due to drug being absorbed but not yet ‘hitting the spot’. IT WILL RARELY BE NECESSARY TO GO DEEPER THAN STAGE 3-4 ABOVE.
- Take your time (same as number 1, but it is that important!)
- When you take the fish out of water for a procedure, lay it on a wet towel and cover the eyes and tail with the towel, ideally have assistance who can 'control' the fish while you do what is necessary
- Have your container of fresh water available for recovery. Its often safer and easier to use containers for recovery rather than simply immediately returning fish to the pond.
Vetark Aqua-Sed is a phenoxethanol anaesthetic. It's a liquid with a very wide safety margin and has been used for anaesthetising fish for many years (reports go back to 1943!)
Aqua-Sed also presents a significant leap forward for petfish welfare; it carries instructions on how to humanely euthanase petfish, by calmly and quietly overdosing them.