Frontal filament morphogenesis in the salmon louse Lepeophtheirus salmonis

The objective of the present study was to understand how and when the frontal filament (FF) in the salmon louse Lepeophtheirus salmonis is produced by examining the sequence of morphological changes leading to FF production in the copepodid and early chalimus stages.

Atlantic salmon (Salmo salar) were heavily infested with 8 day post-hatch copepodids. Sea lice were sampled prior to infestation and at 1, 2, 3, 4, 5, 6, 7, 8, and 9 days post-infestation (dpi). FF morphogenesis from late copepodid to chalimus II (ie. through 2 moults) was studied using high resolution light microscopy of serial transverse and sagittal resin sections. Some histochemistry of the FF was determined using periodic acid-Schiff (PAS) and alcian blue staining. Previous studies by others have shown the FF to consist of a basal plate, stem and external lamina. Three groups of cells, identified as A, B and C, are thought to be involved in the production of the secretions (S1 and S2) which form the filament material. (Abstract shortened by UMI.).