Abstract

Lepeophtheirus salmonis (Krøyer, 1837) represents a major biological challenge in Atlantic salmon aquaculture. Despite extensive research on salmon lice biology, host interaction, and immunomodulation, the mechanisms underlying early host recognition and attachment remain poorly understood. Microscopic examination of the infective stage revealed a previously undescribed spike-like structure in the anterior rostral region of the copepodids. The structure appeared flexible, moved synchronously with body movements, and was present prior to exposure to host tissues or detectable host contact. Behavioral observations further revealed that copepodids actively probe salmon skin explants and fins with their anterior appendages before initial attachment, often followed by prolonged immobility. Scanning electron microscopy suggested that the structure may exist in both protruded and retracted forms and revealed a crevice- or pore-like feature at its proximal end. It is hypothesized that this structure may contribute to early host interrogation through localized sensing and the initial attachment process. These findings highlight a component of early host–parasite interactions and may contribute to future strategies to disrupt host recognition mechanisms in salmon lice.

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