Introduction

Protozoan parasites from marine fishes have not been extensively studied (Lom, 1984). This situation is surprising, bearing in mind that some organisms, long considered as benign, have now been implicated in pathology (Sindermann, 1985). Furthermore, marine pisciculture is increasing in importance, and more extensive supporting knowledge of protozoan parasites is needed (Lom, 1984). Within the protozoa, the phylum Sarcomastigophora, which includes flagellated organisms, is one of the least studied groups (Moller and Anders, 1986).

Review

Diplomonad flagellates belonging to the genera Hexamita and Spironucleus (of the subfamily Hexamitinae), are frequently recorded from the intestine of fish (Kulda and Nohynkova, 1978). The most frequently studied species is Hexamita salmonis, commonly associated with pathology in juvenile salmonids. Spironucleus is potentially pathogenic to cichlids and cyprinids.

Since the early twentieth century, a variety of marine fish have been reported to carry Hexamita. However, the flagellates have often been inadequately described, on the basis of light microscopy only, and it has been suggested (Becker, 1977; Kulda and Nohynkova, 1978) that purely marine species may be conspecific with H.salmonis, the hosts of which are often anadromous. More recently, the location of the kinetosomes (flagellar bases) and the anteriorly situated nuclei - features which are visible ultrastructurally -have been shown to be reliable features for distinguishing Hexamita and Spironucleus, (Brugerolle et al., 1973; Brugerolle, 1974).

The ways in which diplomonad flagellates cause pathology is poorly understood. A close relationship between flagellates and intestinal tissue has been reported for Spironucleus meleagridis in turkeys and Spironucleus muris in mice (causative agents of catarrhal enteritis and catarrhal duodenitis respectively) (Kulda and Nohynkova, 1978). In teleosts, there have been few ultrastructural studies of diplomonad flagellates and their associated host tissues.

Work in Progress

Recently, zoomastigophora resembling H.salmonis were observed in the rectum of Atlantic Cod, Gadus morhua L.(Morrison, 1987).

A variety of light microscope techniques, and scanning electron microscopy, have subsequently been used to study these flagellates, (as was described at the IAAAM meeting in 1988). Whilst these methods have yielded some details of morphology, they were not sufficient to permit identification to genus level. The most reliable features used to distinguish Hexamita and Spironucleus, namely the position of the anterior kinetosomes relative to the nucleus (antero-lateral in Hexamita and antero-medial in Spironucleus, (Brugerolle et al., 1973; Brugerolle, 1974; Lee,1985), could only be determined with certainty by transmission electron microscopy. Ultrastructural studies on the flagellates from the rectum of Atlantic Cod have shown the relationship between different shapes of flagellates, their identity, and their relationship with the rectal epithelium.

References

1.  Becker, C.D. 1977. Flagellate parasites of fish. In Kreier, J.P. (ed.) Parasiric Protazoa Vol.1, Academic Press, New York, pp. 357 - 416.

2.  Brugerolle,G.1974. Contribution a l'etude cytologique et phyletique, des diplozoaires (Zoomastigophorea, Diplozoa, Dangeard, 1910). 111. Etude ultrastructurale du genre Hexamita (Dujardin, 1836). Protistologica. IX, 3, 339-348.

3.  Brugerolle, G, Joyon, L. and Oktem,N. 1973. Contribution a l'etude cytologique et phyletique des diplozoaires (Zoomastigophorea, Diplozoa, Dangeard, 1910). IT. Etude ultrastructurale du genre Spironucleus (Lavier 1936). Protistologica IX 4, 495 - 502.

4.  Kulda, A. and Nohynkova,E, 1978. Flagellates of the human intestine and of intestines of other species. In Kreier, J.P. (ed.) Parasitic Protozoa, vol. IT, Academic Press, New York, pp, 1 - 138.

5.  Lee, J.J. 1985. Mastigophora:Order 7. Diplomonadida. In Lee,J.J., Hutner,S.H. and Bovee, E.C. (eds), An Illustrated Guide no the Protozoa, Society of Protozoologists, Kansas, pp, 130 -134.

6.  Lom, J. 1984. Diseases caused by protistans. in Kinne, 0, (ed) Diseases of Marine Animals. vol. TV. Part 1. Hamburg: Biologische Anstalt Helgoland. pp. 114 - 134.

7.  Moller,H. and Anders,K, Moller, Kiel, FRG, 365 pp.1986. Diseases and Parasites of Marine Fishes. Verlag

8.  Morrisoc,C.M., 1987. Histology of the Atlantic Cod, Gadus morhua: an atlas, Part One. Digestive tract and associated organs, Fisheries and Aquatic Sciences, No, 98:219pp, Canadian Special Publication in Fisheries and Aquatic Sciences. No. 98:219pp.

9.  Sindermann, C.J. 1985. Recent studies on marine parasites and diseases, In Hargis, W.J. (ed.) Parasitology and Pathology of Marine Organisms of the World Ocean, NOAA Technical Report NMFS 25, US Department of Commerce, pp 7 - 13.