Juvenile Lepeophtheirus salmonis (Krøyer) affect the skin and gills of rainbow trout Oncorhynchus mykiss (Walbaum) and the host response to a handling procedure

Abstract

Infectious Lepeophtheirus salmonis (Kroyer) cause localized inflammation at the site of attachment on the host fish, while the greatest physiological impact occurs with the development of the subadult and adult stages. We exposed Oncorhynchus mykiss (Walbaum) to infectious copepods at 30, 25 and 14 days prior to a net confinement procedure, while a second group were sham infected. Fish were sampled at time zero, 2, 4, and 6 h of continuous net confinement, and at 24 h after 2 h confinement. Plasma Na+, Cl–, gill Na+/K+-ATPase activity and skin mucous cell numbers were measured, and skin and gill condition assessed microscopically. Exposure to copepods resulted in lower numbers of acidophilic mucous cells and poor condition of the skin and gill epithelia. Total numbers of mucous cells were decreased in net confined infected fish only. Plasma Na+ was elevated in all samples from non-infected netted fish, without altered gill Na+/K+-ATPase activity, while infected fish had higher plasma Na+ only at 2 h and increased gill ATPase activity at 4 h. The epithelia of infected fish were more severely affected by the confinement procedure. Exposure to juvenile lice can induce effects that become apparent only when a stressor is applied.