The histopathology associated with the pre-adult and adult stages of Lepeophtheirus salmonis on the Atlantic salmon, Salmo salar L.

Atlantic salmon, Salmo salar L., infected with the pre-adult and adult stages of Lepeophtheirus salmonis were obtained from sea loch cage sites on the west coast of Scotland, and infection experiments were carried out in the laboratory. The motile parasites were retained at the point of attachment by prefixation with cooled alcohol. They were studied using light and scanning electron microscopy. Lepeophtheirus salmonis were found to leave an oval 'imprint' corresponding to the margin of the parasite cephalothorax on the host skin and/or to wedge under its scales. General pathological changes including oedema, hyperplasia, sloughing of cells and cellular inflammation were observed in the host at and around the point of feeding and attachment. In gross lesions, serious damage occurred to the host epidermis with scale loss and haemorrhage a common feature. The most obvious changes were associated with the louse mouthtube, marginal membrane, second antenna, maxilliped and sternal furca