*Article* **Farmed Salmon Show No Pathological Alterations When Exposed to Acoustic Treatment for Sea Lice Infestation**

**Marta Solé 1,\*, Maria Constenla 2, Francesc Padrós 2, Antoni Lombarte 3, José-Manuel Fortuño 3, Mike van der Schaar <sup>1</sup> and Michel André 1,\***


**Abstract:** The use of bioacoustic methods to address sea lice infestation in salmonid farming is a promising innovative method but implies an exposure to sound that could affect the fish. An assessment of the effects of these techniques related to the salmon's welfare is presented here. The fish were repeatedly exposed to 350 Hz and 500 Hz tones in three- to four-hour exposure sessions, reaching received sound pressure levels of 140 to 150 dB re 1 μPa2, with the goal of reaching total sound exposure levels above 190 dB re 1 μPa<sup>2</sup> s. Gross pathology and histopathological analysis performed on exposed salmons' organs did not reveal any lesions that could be associated to sound exposure. The analysis of their otoliths through electron microscopy imaging confirmed that the sound dose that was used to impair the lice had no effects on the fish auditory organs.

**Keywords:** salmon; *Salmo salar*; acoustic trauma; scanning electron microcopy; otolith organ; lateral line; histopathology; vaterite; neuromast
