Ecologic Aspects of Protozoan Infections in Antarctic Fishes1

ABSTRACT. Plankton and fishes are abundant in Antarctic waters. Benthic invertebrates and fishes of the continental shelf are well-known, but the abyssal benthos below the highly productive open ocean is largely unsampled. The fishes are adapted (with antifreeze properties) to temperatures that are often or always below the freezing points of their body fluids. All the major groups of helminth parasites are found in or on these fishes. The few records of protozoa include Cryptobia, haemogregarines, a monoflagellate, the myxosporan Neoparvicapsula, and (in this paper) Ceratomyxa. Myxidium, Zschokkella, and a coccidian. Most of the protozoa were obtained from nototheniid fishes. No protozoa and few, if any, other parasites were recovered from 173 midwater fishes collected from outside of the continental shelf. Differences in infections in different localities and depths are due to many ecologic factors needing much more study of their relations to parasitism. These factors include temperatures, salinities, densities of fish populations, food and feeding habits, migrations of adult and immature fishes, availability of potential intermediate hosts, and marine “snow.”