Sea lice solution

Scientists are developing the potential of wrasse as a cleaner fish. Credit: Andrew Denham Scientists are developing the potential of wrasse as a cleaner fish. Credit: Andrew Denham

Bryan Gibson looks at a possible solution to the issue of sea lice infestation.

Sea lice infestation has been described recently, as “the biggest issue facing the salmon farming industry." However, one sea creature possessing an insatiable appetite for another, plus not being considered particularly good eating by humans, has proven to be an unforeseen benefit for the ballan wrasse, along with improved profitability for Scottish, Irish and Norwegian salmon farmers. 

Aquaculture experts from the University of Stirling are leading the research behind a £4m project to boost production in the Scottish salmon farming industry, having received funding from the Scottish Aquaculture Innovation Centre to embark upon a 42-month experiment in wrasse captive breeding.

UK Atlantic salmon exports are valued at over £1bn, and the Scottish Government has set increased production targets for Scottish salmon to maximise domestic demand and to increase exports to markets such as the USA, France, China and the Gulf States.

Cleaner fish
Scientists from the University’s internationally acclaimed Institute of Aquaculture have helped to develop the potential of wrasse as a cleaner fish, which supports a much healthier and ‘greener’ method of sustainable salmon production.

Cohabitation between salmon and cleaner fish at a stocking level of one cleaner per 25 salmon has been shown to significantly reduce the number of sea lice predating upon farmed and wild salmon; an issue that has been seriously hampering the commercial progression of the farmed salmon industry.

Salmon farmers in Scotland and Norway noticed that fish whose pens had been infiltrated by wild wrasse were infested with far fewer sea lice than in wrasse-free cages, and on closer experimentation it was further discovered that wrasse, like their more southerly coral dwelling cousins, remove and eat lice living on the bodies of their larger neighbours, who appear to appreciate such a valuable service so much, that their hosts appear to have lost all desire to eat their benefactors.

Scott Landsburgh, chief executive of the Scottish Salmon Producers' Organisation said he was hopeful that the project could lead to smaller amounts of chemicals being used in the long-term and eventually boost productivity.

"We as an industry can't completely eliminate sea lice, as they are endemic in the wild, so we will continue to use mitigation measures such as using cleaner fish and washing salmon in hydrogen peroxide at low concentration to dispose of lice,” he said. "If the project is successful it could lead to higher yields at fish farms.”

A feature of the project is that the research results will be published in the form of an ‘open knowledge’ handbook so that the whole industry can learn from it for free.

Ballan wrasse have come out on top of other wrasses species such as goldsinny, especially where physical robustness and resistance to disease is concerned, however other species are being tested at fish farms by the industry's biggest salmon producers. The Scottish Salmon Company (SSC) has introduced wrasse at its site at Stockinish off Harris in the Outer Hebrides.

Next year, the company expects to deliver 5,000 two year old wrasse; only just enough to effectively service one fish farm, but the plan is to service tens of sites over the next few years.

At SSC's site at Ardyne, south of Dunoon on the Clyde coast, sophisticated feeding systems are controlled from the shore, so even in the worst winter storms they won't miss-out on dinner.

Farmed wrasse are rapidly becoming a major contributor to the new science which will provide an affordable biological solution to a natural parasite which is currently being controlled by chemicals potentially harmful to the environment.

Steve Bracken of Marine Harvest said that, “if the project is successful in deploying wrasse to control sea lice it will open more sites for use in aquaculture, reduce fish medication costs and boost productivity.”

“Any move by the aquaculture industry to reduce its reliance upon chemicals is welcome,” said Lang Banks, director of WWF Scotland. "Sea lice are a major problem for the Scottish sea farming industry. We welcome this project as an alternative way of dealing with lice, which would not result in so many chemicals leaching into the environment. Although the amount and number are licensed and controlled, but over time they can accumulate in the environment."

The salmon louse can spawn every three days and its lifecycle is dependent upon water temperature, i.e., 90 days with sea water temperature at around 5oC to 19 days at 17oC.

Although there are no records of numbers of farmed salmon discarded due to sea lice infestation each year, one study claims manual handling and chemical disposal represents up to 10% of total production costs, and early indications of the potential cash savings by releasing ballan wrasse into farmed salmon are expected to significantly boost profitability.

Scottish government figures place mortality rate for the 40 million salmon released into the sea in 2013 at 9.2 million (23%). However there are no figures for the eventual number of deaths specifically caused by lice infestation, but it is known that a heavy lice burden causes high blood loss, reduces energy and body weight and spawning condition.  

Wrasse losses can be substantially reduced by providing purpose made fish shelters, anti-bird predation measures and not introducing small wrasse alongside large salmon.

“Devon and Cornwall’s ‘under tens’ are currently experiencing a potential mini fishing bonanza,”, said to Chris Bean, environmentally-friendly under 10m fisherman on Cornwall’s Helford river. “And most environmentally friendly of all, we are being strongly encouraged to land wrasse alive and to maintain them that way, which involves a whole new set of logistics”.

In the absence of a satisfactory supply of farmed cleaner fish, juvenile and semi-mature wrasse are being caught by local small boats, collected from West Country fishing ports by a man with a vivier tank, who transports them to Scotland’s salmon farms, with the fishermen being paid around £6 per kilo.

Scientists are also experimenting with other wrasse species plus lumpfish, which offer the additional benefit of consuming weed growth from netting, which is resulting in an even further reduction in chemical usage.



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