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