DEVELOPMENT OF MYXOBOLUS-NEUROPHILUS (GUILFORD, 1963) (MYXOSPOREA) INTHE BRAIN OF YELLOW PERCH (PERCA-FLAVESCENS) IN VINEGAR LAKE, NOVA-SCOTIA

The development of Myxobolus neurophilus (Guilford, 1963) in the optic tectum of yellow perch, Perca flavescens, inhabiting Vinegar Lake, No va Scotia, is described. Young perch acquired infections during July w hen 2-3 months old. By early August, small plasmodia occurred in the c ortex and consisted of an outer thin ectoplasm and inner endoplasm con taining sporoblasts. By the end of August, plasmodia were found in the brain cortex and periventricular layers. They measured up to 310 mu m in diameter and contained sporoblasts and fully developed spores. Som e plasmodia had ruptured and released spores within the periventricula r layer. It is estimated that in young-of-the-year fish the developmen t of M. neurophilus requires 40-50 days. Prevalence was 100% in fish o lder than 1 year, with infections consisting of spore masses located i n the periventricular layer. Spores were either free in tissue spaces or within unidentified mononuclear phagocytes. Spores were absent from other organs, and spores are probably released when the host dies or when it is eaten by a predator. Macroinvertebrates did not play a role in spore release from carcasses.