Mortality of Eastern Brook Trout Caused by Plerocercoids (Cestoda: Pseudophyllidea: Diphyllobothriidae) in the Heart and Viscera

It is well known that migrating helminth larvae do a great amlount of damage to the host. Often, however, the host is relatively large and the damage done by few larvae is not serious. When the host is very small the niechanical damnage, at least, must be proportionately greater for each larva present. An unusual case of mlortality of smlall brook trout (Salvelinus fontinalis) roughly 2 to 4 inches long was brought to our attention. Examination of the mortalities, as well as survivors, revealed relatively large diphyllobothrid larvae (fig. 1) in the chambers of the heart, liver, pericardial sac, and body cavity. Death of the fish was attributed to hemorrhaging caused by the migrating larvae. Some larvae appeared to be quiescent and were surrounded with sparse connective tissue and very little white cell infiltration. There was