Treatment of fish parasites: 6. Effects of sym. triazinone (toltrazuril) on developmental stages of Glugea anomala, Moniez, 1887 (microsporidia): A light and electron microscopic study.

A symmetric triazinone (toltrazuril) was tested in vivo against Glugea anomala parasitizing the connective tissue of sticklebacks (Gasterosteus aculeatus). Naturally infected sticklebacks were incubated in water containing 0, 5, 10 or 20 μg toltrazuril/ml or in pure solvent (4 ml/1000 ml water). In addition, treatment was done by intermittent therapy (6 × 5 or 20 μg/ml for 4 or 1 h, respectively, in two days intervals). After single treatment the drug caused significant damages on uni- or multinucleate meronts, sporogonial plasmodia, sporoblasts and immature spores. The damages mainly consisted in a decrease of the number of ribosomes, a reduction of the multinucleate meronts, a disturbance in the formation of the sporophorous vesicles, in general a lysis of the karyoplasm and malformations of the polaroplast. The extent of damages was correlated with the dose of the drug administered. After intermittent therapy the damages described above were intensified; the multinucleate meronts and the sporogonial plasmodia then disappeared. However, even by intermittent treatment the mature spores were not affected. It is suggested that chemotherapy of Glugea - infected fishes may be accomplished by bathing the fishes in separate, aerated containers by means of interval treatment (six times with 5 or 20 μg toltrazuril/ml for 4 h, respectively 1 h in two days intervals). The treatment will decrease considerably the output of spores. However, since the mature spores are not affected, a repetition of the interval treatment within several months is recommended. Fish with extended skin lesions, caused by net catching, or infections by fungi should be carefully observed during the treatment, because these factors decrease their drug tolerance.