Abstract
In Atlantic salmon (Salmo salar) aquaculture, the ectoparasitic salmon louse (Lepeophtheirus salmonis) has been one of the main challenges for decades, and a range of measures have been made to prevent and treat infestation. One of these measures is "optical delousing", which identifies the louse on the salmon and targets laser pulses at it, aiming to kill, injure or detach the louse. However, exact effects of the laser exposure on the lice have not yet been described. The current study investigates survival and potential tissue damage of salmon lice after laser exposure.
Salmon lice were collected after controlled laboratory exposure trials as well as from sea cages equipped with commercial laser systems. Visible damage (pigmentation changes) and survival were assessed, and internal and external changes were investigated by histological analysis and scanning electron microscopy (SEM), respectively.
In laboratory trials, survival varied from low to no difference from control, depending on experimental setup. Pigmentation change increased from day 0 (the day of exposure) to day 1, indicating that laser exposure induces pigmentation changes that develop further after exposure. However, visible damage, measured as proportion of total body surface area with visible pigmentation changes, was not a significant predictor of survival for laboratory exposed salmon lice, nor for salmon lice collected from sea cages with commercial laser systems. Results from SEM revealed effects on the cuticle surface, including regions with uneven and disrupted cuticle structure, but only for some of the regions with visible pigmentation change. Histology only showed minor tissue disruption in oviduct organisation, and no other changes were observed compared to control. Salmon lice from sea cages had disrupted cuticle structure in areas with pigmentation change, and tissue necrosis was observed in histology images. The results indicate changes to pigmentation and external and internal tissue following laser exposure, but the current study could not consistently link these effects to each other or survival.