Sea lice is in the news more and more these days as salmon farming companies around the world grapple with outbreaks and their resulting pain to the corporate bottom line.
The financial impact from sea lice on the global salmon farming industry is estimated to run between $600 million and $1 billion annually.
But what are sea lice and what do they actually do to salmon?
Sea lice are copepod crustaceans. Over the millions of years of their existence they have adapted to live on salmon, feeding on fish skin and blood to survive. Lice have a short, free-swimming larval phase, when they need to find and attach to a fish host. The infective larvae are less than a millimeter in length, so finding a host in the wild is more difficult.
But sea lice are able to exploit unnaturally high concentrations of fish found in the cages or pens of salmon farms, where, much like human societies characterized by high densities, diseases can be spread more easily. This means sea lice are able to settle and attach to fish then molt into the pre-adult stage without the immune system of the fish reacting to them.
During the time when they are attached to salmon, sea lice actively feed and “graze” on the skin and the epithelial (tissue) and the mucous layer of the fish. Once sea lice molt to the pre-adult and mobile stages they move and become more pathogenic. At this stage, blood can be detected in a fish’s guts, leading the sea lice to start feeding on that blood.
At the same time, sea lice secrete modulating compounds preventing a fish’s immune response from working properly, allowing sea lice to settle and feed at their leisure.
At this stage a few things happen. With the epithelium damaged the osmoregulatory, or fluid, balance of the fish is compromised, the fish suffer from distress, often reflected in lower feed intake, lethargy and other moribund behaviors. At the same time, damage to the epithilium and immune systems opens a portal to secondary infections linked to virus and bacteria.
IntraFish recently published an exclusive in-depth report on the sea lice and their impact on salmon farming. The report covers the history of the problem, its costs, solutions countries and individual companies are using to combat the problem and a look ahead examining new technology that could help mitigate the problem and reduce costs associated with sea lice.