Treatment of fish parasites. 10. Effects of a new triazine derivative, HOE 092 V, on Monogenea: a light and transmission electron microscopy study.

For chemotherapy of fish parasitized by monogeneans, a novel triazine derivative, 2-[3,5-alpha-dichloro-4-(4-methyl-sulfonylphenoxy)-phenyl]-1-methy l- hexahydro-1,2,4-triazine-3,5-dion (HOE 092 V), was tested in vivo against the gill- and skin-parasitizing species Dactylogyrus extensus, D. vastator, and Gyrodactylus arcuatus. Naturally infected fish were incubated in aerated, separate tanks at 22 degrees C for 1, 2, 3, and 4 h in water containing 0, 1, 5, 10, or 15 micrograms HOE 092 V/ml, whereas Pseudodactylogyrus bini was tested in vitro at 10 micrograms HOE 092 V/ml for 2.25 h. As seen by means of transmission electron microscopy, in vivo treatment against D. extensus caused vacuolization and lysis of the parasite's tegument at a dose as low as 1 micrograms/ml over a 3-h exposure period. Higher doses, such as 5 and 10 micrograms/ml over the same exposure period, produced lesions in the circular and longitudinal musculature of D. extensus and differing degrees of damage to the ciliary cells of protonephridia and immature vitelline cells. There was 100% mortality in D. vastator when incubation was done with 10 micrograms HOE 092 V/ml for 4 h (G. arcuatus; 5 micrograms/ml for 4 h; 10 micrograms/ml for 1 h) and in P. bini after 2.25 h in vitro exposure. In all species tested, the anterior portion and the opisthaptor region were most sensitive to the drug action.(ABSTRACT TRUNCATED AT 250 WORDS)