Ichthyosporidium Hoferi (Plehn & Mulsow, 1911), An Internal Fungoid Parasite of the Mackerel

Abstract

A fungus has been found causing a fatal disease among mackerel in British waters, and a very high rate of infection has been maintained for over three years. It is spread throughout the viscera by the circulation, being particularly common in the kidney and spleen: it is very rare in the muscles and has never been found in the gonads or central nervous system of these fish.Growth of the aseptate, sparsely branched hyphae is usually radial, from one of three types of central body. The length and thickness of the hyphae varies according to the density of the infected tissue and the degree of resistance which is set up. Connective tissue capsules are laid down round spores and hyphal bodies, occluding the small vessels or capillaries in which they become lodged. Growth of the parasite stretches the capsule, which may become a tubular gallery containing many growth stages. This may effectively seal the parasites which then degenerate; or, more usually, the strong proteolytic enzymes secreted by the advancing hyphae perforate it, and proceed to convert the whole organ into a necrotic mass in which hyphae grow to great lengths. There is always a tendency for hyphal walls to collapse behind the outgrowing hyphae, giving the appearance of hair-like threads with swollen ends.Any of the following developments may occur, apparently on any hypha, in tissue undergoing necrosis: (1) Bunches of large elongated chlamydospores, with a very hard exospore and a thick (?) gelatinous endospore—a germination pore is present; (2) Single dome-shaped conidia (like those of Entomophthoraceae); (3) Hyphal bodies of various shapes, either growing at once where they become lodged or becoming rounded and encysted—these may subdivide irregularly, each spherule having a separate cyst; (4) Branched conidiophores with rounded tips which contain endo-conidia—liberated as minute amoeboid bodies into the blood vessels; (5) Simple clavate sporangia from the ends of unbranched hyphae, also containing endo-conidia; (6) Hyphal fusions of numerous kinds, immediately proceeding to further outgrowths of similar hyphae; (7) ‘Spores produced by hyphal fusion’: fusion of two hyphae followed by the participation of neighbouring hyphae which also contribute to form the outer, resistant, rugose wall.

An unusual form of Ichthyophonus hoferi (Ichthyophonales: Ichthyophonaceae) from yellowtail flounder Limanda lerruginea from the Nova Scotia shelf

“…Morphological features of this pathogen from Limanda ferruginea are also similar in some respects to some of the vegetative stages of the Ichthyophonus hoferi from mackerel Scomber scombrus described by Sproston (1944 Sproston (1944) shows that her organism had an ovoid to coralloid thallus with short, stubby, irregularly shaped branches similar to those of the unusual I. hoferi form described herein, and resting spores typical of I. hoferi sensu Plehn & Mulsow, 191 1. Whether all of the developmental stages that Sproston (1944) encountered in mackerel represented those of a single organism is unknown.…”

“…Whether all of the developmental stages that Sproston (1944) encountered in mackerel represented those of a single organism is unknown. It is possible that the infected mackerel studied by Sproston (1944) were infected concurrently with both forms of I. hoferi.…”

Ichthyophonus irregularis sp. nov. from the yellowtail flounder Limanda ferruginea from the Nova Scotia shelf

“…Sproston (1944) described and illustrated morphological forms of Ichthyophonus from mackerel that are similar to the 2 forms we have recovered from the Nova Scotia shelf. T.G.R.…”

Epizootiology of Ichthyophonus hoferi in herring populations off the Swedish west coast

“…Ichthyophonosis has, so far, been reported in marine teleosts from the Pacific Ocean (Munday 1976, Miyaz a h & Kubota 1977, Chien et al 1979, Okamoto et al 1985, Olsen 1986, the Mediterranean (Reichenbach- Klinke 1954, Sitja-Bobadilla & Alvarez-Pellitero 1990, Athanassopoulou 1992, the South Atlantic (Paperna 1986), and most often from both sides of the North Atlantic and adjacent waters (Sproston 1944, McVicar & MacKenzie 1972, Moller 1974, McVicar 1977, 1979, 1980, 1981, Lauckner 1984, Sindermann 1990, Rahimian 1994. The wide ranges of geographic and host distributions suggest that Ichthyophonus hoferi has a very low host specificity.…”