Diplostomulum (Trematoda:Strigeoidea) Associated with Herniations of Bullhead Lenses

Abstract

Autopsies on 144 bullheads (Ictalurus melas and I. nebulosus) from North Dakota and Minnesota revealed a high incidence of diplostomulum-infected lenses. The majority of these lenses possessed dorsally situated cysts. The incidence and intensity of infection varied from one collection area to another, but the cysts typically housed more flukes than the lenses. Anatomical and histological comparisons between normal and parasitized eyes indicate that the cyst results from a herniation of the near the point of attachment of the dorsal ligament. The pressure required for this protrusion appears to come from the parasites, the hyperplastic epithelium, and the reactivity of the substance to the parasites. Cyst production, its effects, and its relationship to host age and worm burdens are discussed. The occurrence of strigeoid metacercariae the lenses and optic chambers of fishes was first reported by von Nordmann (1832). Since then similar cases of parasitism have been recorded from many species of fish, presumably involving many species of flukes. An appreciation of their ubiquitous distribution can be gained from the synopsis of larval strigeoids by Hoffman (1960), and from various fish parasite surveys. Despite these numerous reports there appear to be only two accounts of such flukes being associated with abnormal growths on the fish lens. LaRue, Butler, and Berkhout (1926) reported the localization of diplostomulum metacercariae in small knobs or projections from the lens of Ictalurus nebulosus taken Michigan. More recently Britain Erasmus (1958) noted a rarely occurring tumor-like growth on the lenses of Received for publication 8 June 1964. * From a thesis submitted to the University of Minnesota partial fulfillment of the requirements for the degree of Doctor of Philosophy. This work was supported part by the following: National Science Foundation Fellowship for Teaching Assistants, 1962; National Institutes of Health Predoctoral Fellowship GPM-14,398-R1; and the American Cancer Society Institutional Research Grant IN-13D to the University of Minnesota. t Present address: Department of Biology, University of North Dakota, Grand Forks, North Dakota. Leuciscus idus which had been infected experimentally with Cercaria X Taylor and Baylis, 1930. The present study was undertaken when black bullheads, Ictalurus melas (Rafinesque), were found to possess a high incidence of protrusions on their lenses parasitized by diplostomulum metacercariae. The purposes of this paper are to report the incidence and intensity of infection, and to describe the pathological conditions seen naturally infected bullheads. MATERIALS AND METHODS From 1957 to 1964 autopsies were conducted on 141 I. melas and 3 I. nebulosus collected from North Dakota and Minnesota. Localities, incidence of infection and cysts, and average worm burdens for I. melas are presented Table I. The limited information for I. nebulosus is not included tabular form, although all three specimens were infected. Until dissected all fish were held large tanks supplied with running well water and compressed air. A daily feeding of uncooked oatmeal seemed to provide an adequate diet. The fish were killed by inserting a scalpel into their brains. The eyes were removed with iridectomy scissors and placed 0.6% saline. By using fine forceps, dissecting needles, and microscalpel, the eye could be opened without damaging the or its cyst. The darker dorsal portion of the iris was used as a guide orienting the excised eye prior to opening it. By using a dissecting microscope it was relatively easy to count the flukes within the freshly excised lens. Most of the cysts were too opaque to show all the worms, hence these structures were teased