The Anaesthetic ProcessFish anaesthesia is a continual process that ranges from a slight loss of sensation through to medullary collapse (or death). It is generally accepted that there are five stages of anaesthesia in fish, however for aquaculture operations it is more relevant to refer to three states of anaesthesia: sedation, handleable and deep anaesthesia.
At low concentrations of anaesthetic, as with the 5 mg/L above, a sedated state is reached by the animal and a condition exists where the metabolic clearance rate of the anaesthetic equals the rate of uptake by the animal. In this case the animal will remain sedated and never become fully anaesthetised.
Steady state sedation: Anaesthetic uptake = Metabolic clearance
This steady state is ideal for transport operations where the duration of the treatment may extend for several hours.
At a range of concentrations where the rate of uptake of the anaesthetic is equal to or greater than the rate of metabolic clearance, as with 10 mg/L or higher, the animals are deemed handleable. At these concentrations the animal looses equilibrium and may slowly progress deeper into anaesthesia.
Progression to anaesthesia: Anaesthetic uptake ≥ Metabolic clearance
A concentration that induces handleable animals is ideal for harvesting, grading and stripping operations as the animal shows no reaction to being handled.
Above a certain concentration of the anaesthetic, as in the 20 mg/L example above, there is a steady progression from loss of reaction to external stimuli, through to loss of equilibrium, then loss of reflex and eventually to total medullary collapse. At higher concentrations, e.g. 40 mg/L, the time to progress to deep anaesthesia is shorter.
Progression to anaesthesia: Anaesthetic uptake > Metabolic clearance
As the concentration is increased the handleable window for the aquaculture operator is reduced. Most fisheries operations will be carried out within the handleable window.
Progression through Anaesthesia Using AQUI-S
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