Tapeworm (Eubothrium sp.) infestation in sea caged Atlantic salmon decreased by lice barrier snorkels during a commercial-scale study

Abstract

Reports of infestation by marine parasitic tapeworms (Eubothrium sp.) and an associated growth reduction in Norwegian farmed salmon are on the rise. With few acceptable treatment options available, due to drug resistance evolution in tapeworms or negative drug impacts on fish, alternative controls against the parasite are in demand. In a 10-month commercial-scale study involving standard sea cages and lice barrier snorkel sea cages of different depths (4, 8, 12 and 16 m), we examined if this depth-based preventive technology primarily used against salmon lice (Lepeophtheirus salmonis) also reduced tapeworm infestation. A submerged net roof opening to a central barrier tube (snorkel) was added to standard cages to move salmon deeper but retain surface access; a cage manipulation that avoids contact with mostly surface-dwelling salmon lice larvae and may also separate fish from calanoid copepods, the intermediate hosts of Eubothrium sp. Salmon populations in unmodified standard cages had higher tapeworm prevalence (63–93%) and abundances (4.6–5.7 Eubothrium sp. fish−1) than those in snorkel cages (20–36% and 0.2–0.6 Eubothrium sp. fish−1). Based on these observations, tapeworm prevention could be another beneficial parasite management outcome of snorkel cage technology or other depth-based prevention techniques against salmon lice.