Dr. Kassai Tibor - Dr. Murai Éva szerk.: Parasitologia Hungarica 9. (Budapest, 1976)

Observations on the Incidence of Dactylo^frus vastator (Monogenea) Dr. Kálmán MOLNÁR Veterinary Research Institute of the Hungarian Academy of Sciences, Budapest ,"Observations on the inpidence of Dactylogyrus vastator (Monogenea)." - Molnár, K. - Parasit. Hung. _9, 35-36. 1976. ABSTRACT. An observation on the incidence during the winter months of naturally acquired D. vastator infection of the giUs of carps is described. The infection was maintained in the carps kept in aquarium at 15-18°C till the end of March next and was transferred to non infected carp fry as well as to crucian carps kept together with the parasitized old carps. The biology of Dactylogyrus vastator Nybelin, 1925 has been studied thoroughly by numerous investigators. It appears to be generally accepted that D. vastator is a parasite of special development, since it is mainly found on fry and most frequent in the warmer months of summer. Among the authors NYBELIN (1925), WUNDER (1929) and PAPERNA (1963) stated that D. vastator disappears from the fry during the autumn and in the next year the infection originates from the overwintering eggs. On the contrary LJAJMAN (1948, 1951) pointed out that some worm specimens may be present in the carp throughout the year. The fall in the number of worms was attributed by LJAJMAN to age-dependent immunity. In BAUER's (1959) experiments also old carps proved to be susceptible to infection with D. vastator. In his view superinvasion immunity was responsible for the decrease of the number of worms. This opinion was supported later by the experiments of VLADIMIROV (1971). According to KOLLMANN (1970b) the Monogenean specimens found during the cool season on the old fish were erroneously identified as D, vastator and they were in fact D. crassus Kulwiec, 1927 specimens. Also KOLLMANN (1968) reported data on the incidence of D. crassus on carp. In the present paper observations are described which prove the presence of D. vasta tor throughout the year. Our Experiments During the investigation of the parasite fauna of the carp and occasional dissections of carps from pond farms several D. vastator specimens were found on the giUs of oneand two-summer old pond fish in the winter months (January and February). Likewise the naturally acquired infection of one-summer old pond carps, placed in aquarium in the autumn months and kept at 15-18°C until the end of March next, was found to persist. In this observation, we placed some January-hatched, uninfected, 2-3 cm long carp fry, and some crucian carp (Carassisus carass.) specimens among the infected fish. In two weeks time numerous D. vastator specimens were found on the gills of both carp frys and crucian carps. In the majority of worms - collected from fry, one-summer carp or crucian carp - the shape and size of the chitinous armatures (hooks and copulatory organs) were characteristic to those of D. vastator as given by KOLLMANN (19 70a). In some cases, however, the measurements of the chitinous armatures corresponded with those described by KOLLMANN (1968) to characterize D. crassus.