Cell and tissue reactions of turbot Scophthalmus maximus (L.) to Tetramicra brevifilum gen. n., sp. n. (Microspora)

Abstract

. Tetramicra brevifilum gen, n. sp, n. is described from the connective tissues throughout the body musculature of turbot Scophthalmus maximus (L.). Uninucleate spores (4.8·2 μm) are characterized by a large posterior vacuole, electron dense inclusion bodies in cytoplasm and nucleus and short filaments with 3–5 coils (50 μm extruded). Sporogony is apansporoblastic and tetrasporoblastic, within a host vacuole. Features of the xenoma (2 mm diameter) include a microvillous surface layer with microtubules and microfilaments and a reticulate nucleus with numerous nucleoli. Adherence between adjacent xenomas results in composite cysts of various sizes and shapes depending on site, being dendritic in the myomeres, arms extending between the fibres. Effects on the host, other than eventual destruction of the host cell, include displacement of muscle fibres in myomeres with loss of attachment to myocommata. Breakdown of the xenoma with release of spores into the connective tissue matrix was associated with a localized necrosis affecting surrounding muscle fibres, with leucocyte infiltration and collagen deposition. Spores phagocytosed by macrophages were destroyed in vacuoles, some with multi‐laminate walls. Experimental infections established by intramuscular injection at marked sites remained localized, which suggested that xenomas afford sufficient scope for spore production without the need of secondary invasion. The swimming efficiency of turbot would be impaired in severe infections leading to lowered growth rates and increased mortality in wild populations due to predation and starvation. Feeding hierarchies exist in turbot and the disease could prove significant in farming conditions.

Tetramicra brevifilum, a potential threat to farmed turbot Scophthalmus maximus

“…The present description is the first record of an epizootic of Tetramicra brevifilum in a turbot farm in northwest Spain. Prior to the present record this microsporidian was only detected infecting wild turbot (Matthews & Matthews 1980).…”

“…All these features are typical of Tetramicra brevifilum as described by Matthews & Matthews (1980). A novel feature was the presence of a large amount of poly-Agglutinin titers and leucocyte numbers…”

“…Matthews & Matthews (1980) described a low prevalence of Tetramicra brevifilum in natural fish populations of turbot, off the north coast of Cornwall (UK). Until now there have been no reports on the prevalence of this parasite in farmed turbot.…”

Epizootic study in a turbot farm: bacteriology, virology, parasitology and histology

“…Characteristic white cysts occurred in the liver and no spores were observed in any other tissues. Microsporidia are a potential threat for turbot culture because heavy infections in some species can lead to the inactivation of a substantial proportion of the body musculature and impairment of swimming (Matthews and Matthews, 1980). (Ehrenberg, 1931) are the most frequently encountered ciliates on the surface of marine fish.…”

“…Ferguson and Roberts (1975) found 3-year-old cultured turbot in Scotland with lethal myeloid leucosis due to Haemogregarina sachai. Matthews and Matthews (1980) reported the microsporidian Tetramicra brevifilum which produced small xenomas that gave rise to large cystic formations in skeletal muscles of turbot along British coasts. Devesa et al (1989) described the presence of the ciliate Cryptocaryon sp.…”