Aquaculture now makes up more than 50 percent of world seafood consumption and this figure needs to increase even further in order to meet future demand from a population that is growing both in number and in buying power. A host of farmed species are now under production, but none are without their issues, and salmon seems to have more than its fair share.
Long the target of attack from environmental NGOs, the global salmon industry continues to strive to improve both its environmental credentials and the quality of production. However, a major issue remains in the form of sea lice (Lepeophtheirus salmonis and Caligus spp), which have a significant effect on many areas of production. Their economic impact has been estimated at EUR 0.1 — EUR 0.2 per kilogram of salmon produced, with total losses of around EUR 300 million per year.
Since the birth of the industry in the 1970s, chemotherapeutants have been the main method of control, but reduced efficacy is now a problem with many of these. In Chile, for example, the development of resistance to one treatment resulted in extensive mortalities, financial loss and increased incidence of additional diseases.
Research has been undertaken with “cleaner fish” such as wrasse for a number of years, but with limited enthusiasm from industry and concern from environmentalists about the capture of large numbers of wrasse from the wild. However, several recent multi-million Euro projects have shown that a biological approach using farmed wrasse could provide the answer to this significant problem.
To put the scale of future wrasse production in context, Scottish salmon producers estimate their need to be around 2 million fish per year and in 2010, just 5,000 were produced.
Alastair Barge, MD of Otter Ferry marine hatchery, which is well known for its halibut production, is undertaking a wrasse project in collaboration with the Scottish Salmon Company, Meridian Salmon Group and marine landlords The Crown Estate. He is concentrating on Ballan wrasse (Labrus bergylta), which grow to the most convenient size for use with adult salmon in sea pens, according to Barge. “There are many factors to consider, not least of which are the mesh size of the fish pen and the appetite of the wrasse for sea lice,” he said.
Otter Ferry currently has around 12,000 fish from a first trial production, which Alastair explained was just enough to “clean” one sea site. His aim is to scale production up to 200,000 fish per year, to provide one-tenth of industry’s requirements, but there are many challenges to overcome on the way.
Nutrition, temperature and gender balance are just three of the areas under scrutiny and project manager David Patterson explained that the latter is currently the most puzzling.
“These fish have a complex social hierarchy which we are trying to understand, and display behavior in which females can become dominant and switch gender. The trick is to get the numbers right in each tank but at present it is still trial and error,” he admitted. “We brought in three new brood males this year to ensure a good supply of fertilized eggs, but they have failed to impress our ladies so far and we don’t know why, but it is all part of the research process!”
Brood wrasse enjoy a varied diet of fresh fish, but juveniles are weaned within six weeks of hatching through copepods and artemia, onto a proprietary feed produced by Skretting and Biomar.
The fish need to be grown in a contained environment for 1.5 to 2 years until they reach 15 centimeters long, at which point they are large enough to be placed in salmon pens to start work. This final stage of the process is also the subject of much research, with protocols for deployment, removal and management of wrasse in the pens being developed.
For Barge, each milestone passed in the hatchery is another step towards resolving the sea lice issue. “I share a universal hope that cleaner fish may eventually provide salmon farmers with a vital new biological tool, and I am very pleased to be part of the development process,” he said.