Helping wrasse adjust to life at sea

MARINE Harvest and Scottish Sea Farms have launched a study to find new ways to help farmed ballan wrasse adjust to life at sea.

At the cleaner fish production facility at Machrihanish, husbandry staff are looking at novel ways to replicate pen conditions within rearing tanks to help the wrasse prepare for their transfer to marine sites, aiming to reduce the time it takes for the fish to become effective lice control.

Cleaner fish already work well alongside salmon. However, farmed wrasse, unlike wild alternatives, can take time to settle in marine cages and begin to operate effectively.

At the moment, farmed wrasse spend their lives in relatively

Ballan wrasse small tanks, with very consistent conditions – such as protected recirculation systems, constant light and filtered intake water. Hatchery staff have introduced a series of features to mimic pen conditions in a ‘conditioning tank’ several weeks before the wrasse go to sea.

Hatchery manager, Paul Featherstone said: ‘The hatchery recircu- lation system has subtle differences in water chemistry compared to oceanic water and the feed we’ve been using is different too.

‘We’ve introduced a natural photoperiod, exposed them to oceanic saltwater, given them more laminaria and hides, introduced agar feed blocks instead of pelllets and changed the direction of the wa- ter flow to make conditions more turbulent, just like in a jacuzzi! Wrasse are creatures of habit and they do not like sudden change, but hopefully we can pre-adapt them to the farm environment, through a transitioning phase.’