Scanning Electron Microscopy of the Scolex of Grillotia dollfusi Carvajal 1971 (Cestoda: Trypanorhyncha)

Abstract

catches from April 30 to May 30, 1977. Fork length and sex of each fish were recorded. Gills were preserved in 10% formalin. Copepods that were attached by a bulla were counted in the laboratory. Prevalence is the percentage of fish infected and intensity is the mean number of parasites per infected fish. Infection was similar on male and female fish. Prevalence and intensity increased with host length (Table I). Copepods were usually attached to the distal tips of gill filaments. Occasionally one or two parasites were attached to the body but these were not counted. Whereas the gills are also one of the major sites of attachment of Salmincola californiensis on adult sockeye salmon (Oncorhynchus nerka) the body surface of young salmon is most frequently infected (Kabata and Cousens, 1977, J. Fish. Res. Board Can. 34: 191-202). Adult copepods were never recovered from the gills of salmon fry (32-58 mm long) and rarely from the gills of juveniles (102-270 mm long). These observations led Kabata and Cousens (1977, loc. cit.) to conclude that with an increase in host size the gill filaments provide a more suitable substrate for attachment of adult copepods. Similar to S. californiensis on sockeye salmon, the prevalence and intensity of S. edwardsii on the gills of brook charr increased with host length. Few fish less than 300 mm long had copepods on the gills, whereas most brook charr greater than 350 mm long were infected. Few fish less than 250 mm long were available for examination from Dickson Lake. However, only one of 931 adult S. edwardsii infecting brook charr (< 250 mm long) in the Moisie River, Quebec was attached to the gills; all others were on the body surface, fins and opercula (Black, Montgomery, and Whoriskey, unpubl.). Thus, as with S. californiensis, the gills seem to become a more suitable site for attachment of S. edwardsii as host size increases.