Morphology of Diplomonad Flagellates: Spironucleus torosa N. Sp. from Atlantic Cod Gadus morhua L., and Haddock Melanogrammus aeglefinus (L.) and Hexamita salmonis Moore from Brook Trout Salvelinus fontinalis (Mitchill)

Abstract

A diplomonad flagellate, Spironucleus torosa n. sp. is described from Atlantic Cod Gadus morhua and haddock Melanogrammus aeglefinus. This is believed to be the 1st confirmed report of Spironucleus from a marine fish. Organisms swimming in the rectal lumen were broadly pyriform to elongate, and measured 10.5-18.6 microns long and 3.2-13.3 microns wide; other elongate organisms were attached to the rectal epithelium, via apical extensions appearing continuous with the microvilli. The posterior end of the body was extended into a caudal projection, on either side of which was a posteriolateral ring-shaped protrusion or torus, with a recurrent flagellum emerging from its centre. A symmetrical system of microtubules and lamellae, forming a "V" in protargol impregnated specimens, supported the flanges of the body surrounding the tori, the tori themselves and the caudal projection. Supranuclear microtubules were an inverted V to U shape in transverse section, and an electron dense band accompanied the cytostomes. Lightly staining homogenous cytoplasm was usually present in the anterior part of the body, the remainder being highly vacuolated with numerous dark granules. In swimming organisms, rough endoplasmic reticulum (RER) was present around the nuclei and cytostomes, and bacteria were occasionally seen in the cytoplasm. In "attached" organisms, RER was reduced, and bacteria were absent. Hexamita salmonis Moore from Salvelinus fontinalis was studied by light and scanning electron microscopy for comparison; its cytoplasm was not highly vacuolated. The two recurrent flagella emerged close together from the blunt posterior end of the body.

Spironucleus vortens, a possible cause of hole-in-the-head disease in cichlids

“…The parasite was absent from these latter organs in fish showing moderate or little disease severity; however, in these instances the infection appeared to be in a state of remission, with fish making a full recovery. Hexamitids are known to closely interact with the gut wall of fish; S. torosa can reportedly attach to the intestinal mucosa (Poynton & Morrison 1990). Post (1983) and Poynton & Morrison (1990) described an intracellular form of Hexamita salmonis undergoing multiple fission within epithelial cells of the intestine.…”

“…Hexamitids are known to closely interact with the gut wall of fish; S. torosa can reportedly attach to the intestinal mucosa (Poynton & Morrison 1990). Post (1983) and Poynton & Morrison (1990) described an intracellular form of Hexamita salmonis undergoing multiple fission within epithelial cells of the intestine. Invasion of the lamina propria and entry of the hepatic portal system could explain the high level of S. vortens observed within the liver of discus in the present study.…”

“…Very few other species of hexamitids from fish have been studied with the aid of electron microscopy. These include Hexamita salmonis, Moore 1922, from freshwater salmonids (Ferguson 1979, Poynton & Morrison 1990, Spironucleus torosa Poynton and Morrison 1990, from marine gadids (Poynton & Morrison 1990) and Spironucleus barkhanus from Arctic char, Salvelinus alpinus (Sterud et al 1998). Prior to the application of SEM H. salmonis Moore 1922, was recorded from skin lesions of angelfish by Nigrelli & Hafter (1947) and Spironucleus elegans Lavier 1936 described from the hind-gut of angelfish (Kulda & Lom 1964a,b).…”

In vitro studies on optimal requirements for the growth of Spironucleus vortens, an intestinal parasite of the freshwater angelfish

“…are parasitic flagellates found in both freshwater and saltwater fish. They have been recorded in marine gadoids, Atlantic cod and haddock (Poynton & Morrison 1990), and Atlantic salmon (Sterud et al 1997). In freshwater fish, Spironucleus spp.…”

Phylogenetic analysis of the SSU rRNA gene from the piscine diplomonad Spironucleus torosus (Diplomonadida: Hexamitinae)

“…Previous studies have recorded Spironucleus torosus Poynton et Morrison, 1990 from several species of gadoid fishes, including the only freshwater gadoid, the burbot Lota lota (L.). Two morphologically different isolates of S. torosus have been described (elongate and pyriform).…”