Laboratory and Field Studies on Glugea stephani (Hagenmuller), a Microsporidan Parasite of Pleuronectid Flatfishes*

Abstract

The microsporidan Glugea stephani is a common parasite of juvenile English sole (Parophrys vetulus) in Yaquina Bay, Oregon. Field observations indicated that fish became infected only in the upper estuary where summer temperatures were above 15C and the incidence of infection reached 79.8% in the late fall. Laboratory infections developed and parasite growth occurred only at or above 15C. The parasite was successfully transmitted to juvenile English sole by brine shrimp (Artemia salina) and amphipod (Corophium spinocorne) vectors as well as by direct ingestion of spores by the host. Infections that resulted from ingestion of spore-carrying vectors were much heavier than those resulting from the direct ingestion of spores. The speckled sanddab (Citharichthys stigmaeus), a nonpleuronectid flatfish, and chum salmon (Oncorhynchus keta) were refractory to G. stephani infection in the laboratory.

Modes of transmission of Loma salmonae (Microsporidia)

“…Xenomas in donor fish ( (Lom 1969, Awakura 1974, McVicar 1975, Leiro et al 1994. Water-borne infections can result from direct immersion in a spore solution (Awakura 1974(Awakura , T'sui et al 1988, or by feeding a crustacean, previously exposed to spores, to fish (Awakura 1974, Olson 1976, 1981. L. salmonae has been transmitted per os to chinook (Kent & Dawe 1994) and rainbow trout 0. mykiss (Speare et al 1998a).…”

The microsporidian polar tube: A highly specialised invasion organelle

“…Other species have demonstrated spore discharge at both acidic and alkaline conditions (Hashimoto et al, 1976). Dehydration by drying or hyperiosmotic solutions followed by rehydration has been effective in promoting spore discharge in some species, while dehydration followed by rehydration at an alkaline pH was effective in others (Olson, 1976;Undeen and Epsky, 1990). Various cations including potassium, lithium, sodium, cesium and anions such as bromide, chloride, iodide and fluoride have been used to promote discharge (Undeen and Avery, 1988;Undeen and Epsky, 1990;Frixione et al, 1994).…”

Microsporidian xenomas in fish seen in wider perspective

“…are easily transmitted via crustaceans acting as transport hosts. Olson (1976Olson ( , 1981 found that spores of Glugea stephani elicited heavier infections after passage through crustacean digestive tract than when produced by intraperitoneal injection. He even suggested that amphipods might represent a natural route of transmission for G. stephani.…”