Newcomers to aquaculture may be surprised to think of fish farmers needing to sedate their fish, but this is in fact a common practice.  Fish are routinely sedated for a variety of reasons including sorting, grading, transporting, spawning and disease treatment.  Furthermore, fish are not unique in receiving this treatment as a wide range of aquatic animals are sedated, including crustacea and molluscs.

 
A range of products can be used to sedate fish, including Aqui-STM, clove oil, MS-222, benzocaine and 2-phenoxyethanol.  The choice of drug and dosage depend on the purpose of the sedation, frequency, cost, availability and ethical considerations.  Some have a wide safety range whereas others need to be used with far greater care.  All chemicals are added to the water housing the animal to be sedated, and the drug acts by entering the bloodstream via the gills.
 
Different terms are used to describe the process, including sedation, anaesthesia and euthanasia.  In essence they are steps on a continuum which can be fairly clearly marked out as being:
 
1.     the first stage is excitement whereby the animals try to escape their container
2.     then behaviour becomes depressed, the animal is unresponsive and respiration slows, this is sedation and is used for mass handling, sorting, grading and transporting fish
3.     next, there is a loss of equilibrium and the gill movement slows even further, at this point the animal is anesthetised and ready for radical handling such as surgery
4.     eventually breathing stops completely and the animal dies, this is euthanasia and is useful kill an aquatic animal humanely (such as for slaughtering or culling)
 
To achieve a more advanced level along the equilibrium a higher dosage of chemical is used or the duration increased.  Once the desired level of relaxedness is achieved the animal can be removed from the solution and handled as required.  To reverse stages 2-3 simply return the fish to a tank of clean water and they should fully recover well inside of 5 minutes.
 
The dosage required varies according to water temperature, water quality, fish species, fish size and stock density, requiring some trial and error initially to establish appropriate dosages for a new species.
 
For those wanting to sedate or anaesthetise their aquatic animals we are the African agent of the Aqui-STM brand which has been specifically developed for use with aquatic animals.  Send us an email to find out more about the product or place orders.