We have, once in a lifetime, heard that two species are living in a symbiotic relationship.

But exactly what does that mean?

A symbiotic relationship, also known as symbiosis, is a close ecological relationship between two or more individuals of different species. It can be beneficial to both species, harmful to one, and beneficial to the other, or not affect either.

Parasitism is a type of symbiotic relationship. In this type of relationship, one specie gets benefits at the expense of the other.

One example of parasitism is sea lice on salmon fish.

Sea lice are copepod crustaceans. They have been around for millions of years and have adapted to living on salmon. They feed on the fish’s skin and blood to survive. The sea lice cause physical harm and stress to the fish, and negatively affect their growth and performance. Severe infestations can result in secondary infections and mass mortality.

Because the infective larvae of sea lice are less than a millimetre long, finding a host in the wild is a difficult part of their life cycle. However, in aquaculture, fish are kept at unnaturally high densities, which parasites will exploit and make their lives easier. Due to this, fish farms are experiencing a great loss, as a minor infestation of sea lice can make salmon unmarketable. The economically sustainable farming of salmon is not possible without controlling parasitic infestations. The possible approaches for controlling parasitic infestations are chemical treatments or veterinary medicine.

Emamectin Benzoate

Emamectin benzoate is a macrocyclic lactone. It belongs to the naturally occurring Evermectin family of insecticides. In agriculture, it is used to control insects on various crops such as groundnuts, cotton, soybeans, safflower, and vegetables.

In aquaculture, it is the active ingredient in veterinary medicines specifically prescribed for sea lice. Emamectin has shown efficacy against all the life cycle stages of sea lice.

For the treatment of sea lice on salmon, it is administered by in-feed treatment. The in-feed treatment is favourable because it provides long-term protection (up to 62 days) against sea lice. In fish, it is absorbed by the gut and distributed to tissues, and then excreted in faeces after metabolization. The parasite consumes it via fish tissues and then dies due to disturbed neurotransmission, which leads to paralysis.

Dosage 

A daily dose of 25μg to 400μg of emamectin or salt thereof per kg of fish biomass for 3–14 days is beneficial in the prevention or elimination of parasites from the fish population.

One-third of the world’s population is dependent on fish for their protein diet, and fish farmers are dependent on fish for their income. But this sea lice infection is affecting this adversely. To prevent sea lice infection, emamectin benzoate containing veterinary medicines is a great solution.