The Sea Lice Threat to Salmon Farms
Published on Apr 11, 2018

It’s no secret that fish farmers consider sea lice to be the biggest threat to the global aquaculture industry. Not only do sea lice infestations contribute to health problems for both farmed and wild salmon, but additionally, the rise of sea lice worldwide has resulted in a global uptick in salmon prices for consumers. Scientists and researchers are working quickly toward new safe and sustainable methods for eliminating sea lice infestations without harming the salmon while considering the complex history of sea lice treatment.


Sea lice are crustacean parasites that attach themselves to host fish skin, gills or fins and feed off the mucus and skin of the fish. Left untreated, sea lice infestations may result in death due to exposed tissue, bacterial infections, or extreme stress. Sea lice may also lower the efficiency of the immune system, making fish more susceptible to diseases they might otherwise fend off easily. Even when not lethal, sea lice can cause injuries severe enough that the fish are no longer suited to sell at market. It’s worth noting that although no one wants a sea louse to show up on their dinner plate, they are not harmful if consumed by humans.


Sea lice are not a new threat to salmon. They have always been present in the wild, but flourish to higher levels in the dense populations of a salmon farm. As salmon and trout aquaculture expanded globally in the late 90s and early 2000s, farmers saw increasing infestations of sea lice, and began treating their fish with emamectin benzoate, a pesticide more widely known as SLICE™. Due to its efficacy, ease of use and relative safety, SLICE™ became the drug of choice for fish farmers combating infestations. But the tiny parasites eventually developed a resistance to SLICE™, and in the past decade, researchers have started looking for new methods to combat the sea lice threat as SLICE™ treatments grew less effective.

“Our work has to be quicker than the evolution of the lice,” said Jake Elliot, vice president of Cooke Aquaculture, in an article about the challenges of sea lice published in the UK Independent last year.


Designed to minimize harm to salmon, the environment, and human salmon-consumers, new weapons in the fight against sea lice are proving surprisingly creative. A few highlights from recent auspicious developments include:


Research on farming salmon symbiotically with other fish and mussels is underway. Growing salmon alongside a second species that consumes the sea lice and controls their numbers has shown to have promising results for fish farmers worldwide, including using the lumpsucker in Norway, the Ballan wrasse in Scotland, and mussels in Maine.


In Norway, Beck Engineering has designed a louse-targeting underwater drone called the Stingray that searches and destroys sea lice from a distance of two meters. Using a combination of recognition software, cameras and a diode laser, the Stingray autonomously identifies lice and fires laser pulses safe enough for fish scales but more than capable of barbecuing a louse.


Salmon are unique in that they can survive in both salt water and freshwater. Sea lice however, cannot. In this method for removing sea lice, fish move through a system of closed columns, and a jet of water rinses the lice off of the fish. By bathing the salmon in freshwater before harvest, fish farmers are able to kill large numbers of sea lice without harming the fish, introducing drugs or pesticides, or any chemical discharge to the environment. Last year, Marine Harvest began using reverse osmosis on board a well-boat in order to desalinate sea water for freshwater salmon treatment - with highly effective results and zero fish mortality.


Medicinal baths continue to be used widely to treat sea lice. However, chemical and medicinal treatments, and the subsequent release of these components into sea water, remain one of the biggest objections to the aquaculture industry. By combining these treatments with water purification methods, chemical removal of sea lice may become a safer option for salmon farmers. Late last year, CleanTreat delivered their first commercial-scale field trial of a proprietary purification system engineered to remove all medicinal components from treatment water before discharge to the ocean. The treatment resulted in 100 percent efficiency in removing sea lice, as well as proving environmentally friendly.


Permeable fabric skirts around the top six meters of the pen combined with a strong oxygen aeration system has proven successful for some salmon farmers, as well. The fabric provides a barrier against sea lice often found near the surface. Oxygen bubbles from aeration systems deliver water from deeper depths so the sea pen skirts stay on when oxygen conditions are critical. Read more about how Pentair AES sea pen aeration solutions can help mitigate sea lice, in addition to algae blooms and other harmful plankton.

As research continues to move forward, it’s not likely that a single tactic will emerge as the magic bullet for treating sea lice infestations. It’s much more likely that the industry will find a combination of new and old methods that prove to be the safest and most effective treatment for this scourge upon salmon.