Ichthyophonus hoferi Plehn & Mulsow in British Columbia stocks of Pacific herring, Clupea pallasi Valenciennes, and its infectivity to chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Abstract

Pacific herring, Clupea pallasi Valenciennes, collected from three areas of coastal British Columbia were screened for Ichthyophonus by histological examination. The infectivity of Ichthyophonus to juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum), was examined in laboratory studies. Ichthyophonus was detected in a total of 82 of 356 herring from all three areas. Prevalence in 2000 and 2001 ranged from 10.5 to 52.5% and was significantly lower in more northern (Hecate Strait) samples. Ichthyophonus was detected by histological examination in chinook salmon following oral or intraperitoneal (i.p.) exposure to homogenates of infected herring tissue. Infections in Yukon stock chinook salmon were occasionally associated with mortality and with inflammation in all tissues examined. Infections were detected significantly more frequently in the caecal mesenteries of i.p.‐infected compared with oral‐infected chinook salmon. The distribution and prevalence of Ichthyophonus isolates among diverse host species may assist in stock identification and in an improved understanding of trophic interactions.

Phylogenetic interpretations and ecological potentials of the Mesomycetozoea (Ichthyosporea)

“…In fish large epizootics of Ichthyophonus have been reported in herring from the North East Pacific (Hershberger et al 2002) and pre-spawning mortality due to both Ichthyophonus and Dermocystidia has been described in salmonids (Pauley 1967;Kocan & Hershberger 2006). All three Mesomycetozoea genera which cause diseases in fish are known to have broad host ranges, and transmission studies with Ichthyophonus and Sphaerothecum have demonstrated that, at least in some circumstances, host specificity is not parasite species specific (Jones & Dawe 2002;Andreou et al 2012). It is not known whether there are species within these genera that can infect both fish and amphibians.…”

“…I. hoferi causes the disease ichthyophonosis and can seriously affect aquaculture as the disease is easily spread via the fish skin or via the urinary tract if the kidneys are infected (Ramaiah 2006). Laboratory experiments have shown that infection of Ichthyophonus can spread up through the food chain from herring to Chinook salmon (Jones & Dawe 2002). However, although cells of Ichthyophonus leak out through the fish skin, experiments have shown that there is no transmission of infection when healthy herring are exposed to infected herring (Gregg et al 2012).…”

Assessing the accuracy of a polymerase chain reaction test for Ichthyophonus hoferi in Yukon River Chinook salmon Oncorhynchus tshawytscha

“…Salmonids are also susceptible to this parasite (Jones & Dawe 2002, Schmidt-Posthaus & Wahli 2002. Kocan et al (2004) conducted an extensive, multi-year survey of I. hoferi in Chinook salmon Oncorhynchus tshawytscha (Walbaum, 1792) from the Yukon River from 1999 to 2003.…”

Amplification and transport of an endemic fish disease by an introduced species

“…Incomplete species descriptions fail to provide sufficient detail to allow unequivocal identification of the parasite to the species level (Alderman 1982); consequently, it will hereafter be referred to generically. Since its first description in the NE Pacific during the early 1980's (Olson 1986), Ichthyophonus has become recognized as ubiquitous in many marine fish populations throughout the region (Marty et al 1998;Kent et al 2001;Hershberger et al 2002;Jones and Dawe 2002) where it has been associated with population-level effects (Marty et al 1998;Hershberger et al 2002;Kocan et al 2004). Causes for its apparent recent emergence in the NE Pacific (Kent et al 2001) remain undetermined.…”