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Signs of Recovery

Whichever method of stunning/killing is used, it is important that staff are able to recognise the signs of an effective and ineffective stun. These signs vary depending on the species. It is essential when deciding on a method to check that it is reliable and effective for that species. A number of tests can be performed on salmon and trout to check whether they are conscious or unconscious. These are outlined in the following table.





Eye roll

Eyes remain on the same plane as the fish is rotated.

Eyes do not move as fish is rotated.


Regular movement of the operculum.

No/random movement of the operculum.


Fish constantly swimming.

No movement or attempt to swim.


Fish will right itself when knocked.

Fish will remain upside down.


Fish may move away from the stimulus.

Fish will not move away from the stimulus.

Electric current*

Fish may move away from the stimulus.

Fish will not swim away from the stimulus.

*These tests do not always provide conclusive results: some fish may not show a reaction to these stimuli when fully conscious.


The most reliable and effective signs of recovery for salmon and trout are the return of the eye roll reflex (Figure 11) and the breathing reflex. Rhythmic movement of the operculum should be looked for, but take into account that apparently random and irregular movements can be, but are not usually, a sign of recovery.

Eye roll

Figure 11: Signs of recover in fish - the eye roll reflex1

1 Adapted from 'Protocol for assessing brain function in fish and the effectiveness of methods to stun and kill them'. SC Kestin, JW van de Vis, DHF Robb. The Veterinary Record, March 9 2002.

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