Introduction
Atlantic Cod, Gadus morhua, and Haddock, Melanogrammus aeglefinus, are two of the most economically important fish from the east coast of Canada. There have been a number of studies of their metazoan fauna [as discussed by Appy (1978) and Appy and Burt (1982)], but by comparison, the protozoan fauna has received little attention. Our investigations have considered endoparasitic flagellates.
Review
Flagellates of the order Diplomonadida, Family Hexamitidae can parasitize a wide range of hosts including the mouse, turkey, pigeon, tortoise, amphibians, fish, oysters and man, and many species are pathogenic or potentially pathogenic (Kulda and Nohynkova, 1978). The family comprises four parasitic genera, having trophozoites that are axially symmetrical, with eight flagella, two nuclei and a double set of accessory organelles.
Two subfamilies, Hexamitinae and Giardiinae, are differentiated according to ultrastructure and food intake. In Hexamitinae, which includes the parasitic genera Hexamita and Spironucleus, the two recurrent flagella passing through the body are accompanied by accessory organelles which form hollow tubes. These tubes open posteriorly and function as cytostomes. In Giardiinae, which include the parasitic genera Octomitus and Giardia, the accessory organelles may be developed to elaborate axial columna or reduced to a microtubular band, both having cytoskeletal functions (Kulda and Nohynkova, 1978).
There has been much confusion in the literature concerning taxonomy of diplomonad flagellates from the intestine of fishes (as noted by Kulda and Lom, 1964). A number of records noted the presence of a particular genus, but were not accompanied by adequate supporting descriptions. Some generic and specific designations have been revised, and diplomonad flagellates recorded from the intestine of fishes are now considered to belong to the Hexamita or Spironucleus genera (Kulda and Lom, 1964). Hexamita salmonis is frequently recorded from the intestine of salmonids, and has often been associated with mortality of young fish in culture conditions. Spironucleus elegans is repeatedly found in the hind gut of ornamental typical fish (Kulda and Lom, 1964).
Work in Progress
In 1987, Morrison noted the presence of Zoomastigophora in the rectum of cod from the Atlantic coast of Canada, and the arrangement of the flagella, as shown by scanning electron microscopy suggested that these organisms may belong to the order Diplomonadida [as defined by Levine et al., (1980)]. Other workers [including Lavier, (1936) and Noble, (1957)] have recorded Hexamita in marine fish.
During 1987 and 1988 we therefore studied the flagellate fauna in the rectum of cod and haddock. Light and electron microscopy techniques were used to confirm the identity of the organisms, Brugerolle, (1974) and Brugerolle, Toyon and Oktem, (1973, 1974)] demonstrated the importance of ultrastructural studies in the taxonomy of this group of flagellates. The prevalence and intensity of infection in wild fish was monitored.
References
1. Appy, R. G. (1978) Parasites of cod, Gadus morhua L., in the Northwest Atlantic Ocean. Ph.D. Thesis, University of New Brunswick, Canada.
2. Appy, R. C. and Burt, M. D. B. (1982) Metazoan parasites of cod, Gadus morhua L., in Canadian Atlantic waters. Can. J. Zool. 60: 1573-1579.
3. Brugerolle, G. (1974) Contribution a l'etude cytologique et phyle'tique des diplozoaires (Zoomastigophorea, Diplozoa, Dangeard, 1910). 111 E'tude ultra-structurale du genre Hexamita (Dujardin, 1836) Protistologica. TX, 3, 339-348.
4. Brugerolle, C., Joyon, L., and Oktem, N. (1973) Contribution a l'etude cytologique et phyle'tique des diplozoaires (Zoomastigophorea, Diplozoa, Dangeard 1910) 11. Etude ultrastructurale du genre Spironucleus (Lavier 1936). Protistologica IX, 4, 495-502.
5. Brugerolle, G., Joyon, L., and Oktem, N. (1974) Contribution a l'etude cytologique et phyle'tique des diplozoaires (Zoomastigophorea, Diplozoa, Dangeard 1910). IV Etude ultrastructurale du Octomitus (Prowazek, 1904). Protistologica X, 4, 457-463.
6. Kulda, J. and Lom, J (1964) Remarks on the diplomastigine flagellates from the intestine of fishes. Parasitology 54, 753-762.
7. Kulda, J. and Nohy'nkova', E. (1978) Flagellates of the human intestine and of intestines of other species. pp I - 138 in Kreier, J.P. Parasitic Protozoa Vol. II Intestinal Flagellates, Histomonads, Trichomonads, Amoeba, Opalinids and Ciliates. Academic Press. Inc. New York Lavier, G. (1936) Sur quelques flagelles intestinaux de poissons marins. Annls. Parasit. hum. comp. 14, 278-289.
8. Levine, N.D. et al., (1980) A newly revised classifcation of the protozoan. J. Protozool. 27(1) 37-58.
9. Morrison, C. M. (1987) Histology of the Atlantic cod Gadus morhua: an atlas. part one. Digestive tract and associated organs. Can. Spec. Publ. Fish. Aquat. Sci. 98: 219p.
10. Noble, E. R. (1957) Seasonal variations in host-parsite relations between fish and their protozoa. J. Mar. Biol. Ass. U.K. 36, 143-155.