First endozoic record of a trichodinid ciliate in fish (note)

Abstract

Unidentified trichodinid ciliates (Protozoa: Ciliophora: Urceolariidae) were recorded within the tissues of the New Zealand freshwater eels, Anguilla australis schmidtii (Phillips) and Anguilla dieffenbachii (Gray). Organisms were small, measuring approximately 10 μm in diameter, and it is not known how they enter the eels. This is thought to be the first recording of usually ectoparasitic trichodinids occurring within their hosts. OBSERVATIONS AND DISCUSSION During a haematological study of the New Zealand freshwater eels, Anguilla australis schmidtii (Phillips) and Anguilla dieffenbachii (Gray), trichodinid ciliates were found. These occurred in routine blood films, and liver and splenic imprints. Organisms were smaller than Trichodina microdenticula from North America. T. microdenticul a was the smallest of 17 species described by Wellborn (1967), and measured 22-37 ij.m. Trichodinids from New Zealand eels had a diameter of approximately 10 jum after fixation in methanol. They possessed the characteristic adhesive disc supporting a ring of denticles, which are uniform structures in this group of ciliates. Identification relies partly upon the diameter of the adhesive disc and denticular ring. The number, length, and shape of denticles and radial pins are also important features of trichodinid taxonomy. Trichodinids are common and sometimes pathogenic ectoparasitic ciliates of marine and freshwater fishes (Jones 1974). They are also found on amphibians, coelenterates, and polychaetes, where they skim about on the mucus surfaces of skin, gills, fins, and palps. Occasionally, they are entozoic as in the urinary bladder of amphibians (Fulton 1923), but to the knowledge of the author there are no records of trichodinids being located within their hosts. How they gain entry to the host remains a mystery; they possibly entered through a lesion, for the parasites are of small size, and some fish did have scars remaining from previous small wounds. It may be significant that these organisms were located in the tissues of the reticulo-endothelial system, and that they were in the process of being filtered from the circulation. The fact that trichodinids lack marked host specificity (Lom & Homan 1964) suggests that the group are opportunistic, although it is not known if the organisms were alive when found.