The effects of Salmincola californiensis (Copepoda: Lernaeopodidae) on the gills of farm-raised rainbow trout, Salmo gairdneri

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Abstract
Salmo gairdneri from an Iowa trout farm were found to be infested with Salmincola californiensis. Examination of gills from 235 trout revealed a prevalence of 83% and a mean intensity of 4.6 copepods. Preferred sites were established with the adult female attached usually on distal ends of the gill filaments or on gill bars and the chalimus attached to proximal regions of gill filaments. Examination of hematoxylin and eosin stained tissue sections of attached adult females revealed hyperplasia and hypertrophy ("tumor of attachment") and atrophy or growth inhibition ("crypting") of affected gill filaments. Eosinophilia and absence of mucous cells occurred in gill filaments affected by feeding activities and bulla attachment. Hyperplasia of the gill filament cartilaginous rod and resulting formation of a cartilaginous "bridge" between bulla and filament rod is described. Chalimus attachment elicited hyperplasia and frequently fusion of basal elements of adjacent gill filaments. Activities of adult females attached to gill bars resulted in proliferation of stratified squamous epithelium, infiltration of granular leucocytes and reduction of mucous cells. Damage to gill tissues of trout maintained in dense populations offish culture is deemed significant, especially during summer periods of low dissolved oxygen.

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