Masters Thesis

Incidence, intensity, and seasonal variation in Schistocephalus solidus infections of three-spined sticklebacks (Gasterosteus aculeatus L.) from the San Joaquin River, California

A population of three-spined sticklebacks Gasterosteus aculeatus L. from the San Joaquin River below Friant Dam near Fresno, California, was found to be infected with the plerocercoid larval stage of a pseudophyllidean cestode, Schistocephalus solldus (Muller, 1776). Schistocephalus solidus belongs to the class Cestoidea, subclass Cestoda, order Pseudophyilidea, family Dibothrio- cephalidae. During the plerocercoid larval stage it is a coelomic tapeworm of the three-spined stickleback Gasterosteus aculeatus. Members of this genus are widely distributed in many parts of the world, with the majority of infections being reported in Great Britain and Ireland (Smyth, 19-4-6; Hopkins and McCaig, 1963; Arme and Owen, 1967; Chappell, 1969a,b; and Pennycuick, 1971a, b, c, d. In California, S. solidus has been studied by Markley (19^-0) and Haderlie (1953). The present study will: (1) demonstrate the seasonal incidence and variation of the parasite infection, (2) indicate the differences in the sizes of the infection in stickle- backs of different sexes and sizes, and (3) show the frequency distributions of the parasite within the host population.

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