Natural remedy on way in bid to keep farmed fish pest-free

The lice restrict the production and growth of farmed fish and threaten their health but researchers are using juvenile ballan wrasse, hatched and reared from eggs at The Deep, to feed on the lice.

Dr Jim Treasurer, head of the research project at the Ardtoe laboratory on the west coast of Scotland, said: "While wrasse have been used for the control of sea lice in Norway, there are environmental reservations about taking wrasse from the wild.

"It was crucial we found a reliable supply of ballan wrasse eggs for rearing in our hatcheries. We are delighted that The Deep could solve our problem."

Aquarists at The Deep introduced wrasse into its "North Sea" tank in 2002.

The eggs are removed three to four days after being laid and sent to Scotland, where they hatch into fry after 10 days. The juveniles weigh about nine grammes at a year old.

Senior aquarist Richard Oades said: "We found that our imitation pipeline in our northern seas exhibit was an ideal surface for the wrasse to lay their eggs.

"This meant we had to rapidly develop a method of carefully removing the eggs. This turned out to be a paint brush and turkey baster."

The Ardtoe team has reared more than 400 ballan wrasse fry which are being monitored to find out how efficient they are at cleaning farmed fish.

Ballan wrasse are common throughout British coastal waters and are found in rocky areas and wrecks. They all begin life as females, which are maintained in a harem group by a single male. If the male dies or leaves, the largest female of the group changes sex.V