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
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
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.
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
“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
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.