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Treatment of fish parasites

II. Morphogenesis ofHenneguya laterocapsulata Landsberg, 1987 (Myxosporea, Myxozoa), and the effects of a new triazine derivative, HOE 092 V, on its developmental stages: a light and electron microscopy study

Abstract

The ultrastructure of sporogenesis was studied inHenneguya laterocapsulata parasitizing the skin of hybrid catfish (Clarias gariepinus x Heterobranchus bidorsalis) in Nigeria. Sporogenesis started when a generative cell was surrounded by a second nondividing cell (i.e., envelope cell). By subsequent divisions of the generative cell, ten cells were produced, which finally became arranged into two spore-producing units. Each unit consisted of a binucleate sporoplasm, two capsulogenic cells, and two valvogenic cells. Apparently capsulogenesis, valvogenesis, and sporoplasm differentiation occurred concomitantly. In research for chemotherapy of fish parasitized by myxosporeans a new triazine derivative, 2-[3,5-α-dichloro-4-(4-methyl-sulfonylphenoxy)-phenyl]-1-methyl-hexahydro-1, 2, 4-triazine-3,5-dion (HOE 092 V), was tested in vivo against the uni- and multicellular developmental stages ofH. laterocapsulata. Naturally infected catfish were incubated in water containing 0, 2.5, 5, and 10 μg HOE 092 V/ml or the pure solvent for 3 h. After the fish had been returned into fresh water, they were killed 1 day after the treatment and the plasmodia were studied by means of light and transmission electron microscopy. Starting with a dose of 2.5 μg HOE 092 V/ml, the pericyte's outer membrane was broken in the bi- and multicellular stages. The number of ribosomes in the bi- and multicellular stages decreased. In the multicellular stages the rough endoplasmic reticula of the capsulogenic cells were enlarged. Treatment with 5 μg HOE 092 V/ml led to breaks in the limiting outer membranes of the capsulogenic cells and to vacuolization of their peripheral cytoplasm. In early prespore stages a decrease in the number of spherical inclusions was recognized. After treatment with 10 μg HOE 092 V/ml the degree of the damage increased and the sporoplasm of the nearly mature pansporoblast shrank. The pure solvent had no effect on either the plasmodia or the uni- and multicellular stages. These results suggest that chemotherapy againstH. laterocapsulata and other myxozoan species should be accomplished by bathing the fish in aerated containers with 5 or 10 μg HOE 092 V/ml for 3 h. This treatment will considerably reduce the production of spores.

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Abbreviations

C:

crista

CA:

chromatin aggregations

CC:

capsulogenic cell

CP:

capsular primordium

D:

destruction of the limiting membrane

EB:

electron-dense body

EC:

envelope cell

F:

fibril

GC:

generative cell

M:

mitochondrion

MI:

microtubulus

N:

nucleus

NN:

nucleolus

PC:

polar capsule

PS:

perinuclear space

R:

ribosome

RER:

rough endoplasmic reticulum

S:

sporoplasm

SR:

sutural ridge

T:

thickenings of the limiting cell membrane

V:

vacuole caused by treatment

VC:

valvogenic cell

VM:

material forming the valve

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Correspondence to Günter Schmahl.

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Schmahl, G., Obiekezie, A. & Raether, W. Treatment of fish parasites. Parasitol Res 79, 667–674 (1993). https://doi.org/10.1007/BF00932509

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Keywords

  • Outer Membrane
  • Dion
  • Triazine
  • Generative Cell
  • Rough Endoplasmic Reticula