Host Response of Atlantic Salmon (<i>Salmo salar</i>) to Infection by Sea Lice (<i>Caligus elongatus</i>)

Abstract

Atlantic salmon (Salmo salar), naturally infected with Caligus elongatus in seapen cages in Brandy Cove, St. Andrews, N.B., were examined histologically and ultrastructurally for signs of pathology associated with the attached chalimus larvae. Naturally -infected fish and fish that had never been exposed to sea lice infections were examined serologically for altered white blood cell counts and for any antibody response to the adult parasite. The chalimus larva feeds on the epidermal cells of the scale to which it is attached and denudes the epidermis down to the basement membrane. Ruptured and pycnotic cells line the hole created by the larva, and there is some evidence of hyperplasia around stage IV chalimus larvae. Little other damage or host reaction is evident. There is no seral antibody response to the patent infection as assayed by electroimmuno transfer blot, and white blood cell counts from infected and control groups of fish are statistically the same.