Effects of on-board storage and electrical stunning of wild cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on brain and heart activity

Cod and haddock captured with commercial trawling gear were taken immediately after landing on deck to on-board storage in dry bins for measuring brain and heart activity, and behaviour. Other groups were first stored in holding tanks and then electrically stunned with a prototype “dry stunner”. For stunning 52 Vrms was applied on individual fish for 1 s. As a result, the cod and haddock received an electrical current of 0.34 ± 0.09 and 0.36 ± 0.12 Arms, respectively. Electrical activity in the brain and heart was measured before and after electrical stunning. The fish remained conscious for at least 2 h after landing and during on-board storage as indicated by the electrical activity measured in brain and heart. Behavioural responsiveness to administered stimuli was absent in both species. After electrical stunning, both species showed a general epileptiform insult which was characterised by a tonic phase followed by a clonic phase and terminating with an exhaustion phase.Since the fish remained conscious after landing and storage, electrical stunning and subsequent killing with a throat cut, may provide an option for improving fish welfare on-board commercial fishing vessels. In particular, we recommend to stun and kill wild cod and haddock as soon as possible after landing on deck using a dry stunner applying 52 Vrms (coupled AC/DC current) for more than 3 s.

► Brain and heart activity remain for at least 2 h after landing on board and during storage on board in dry bins.
► After electrical stunning, fish showed a general epileptiform insult which means unconsciousness.
► The measured current was for cod and haddock on average 0.34 ± 0.09 and 0.36 ± 0.12 Arms, respectively.