DIPLOZOON HOMOIN (DISCOCOTYLIDAE, MONOGENOIDEA), A NEW PARASITE IN POND-REARED HYPOPHTHALMICHTHYS MOLITRIX

Lucky Z.: Diplozoon homoin (Discocotylidae, Monogenoidea), a New Parasite in Pond-reared Hypophthalmichthys molitrix. Acta vet. Brno, 50, 1981: 237 -244. Examination of health status of silver carp (Hypophthalmichthys molitrix) fry from the State Fishery, Pohoi'elice, revealed repeatedly infestation with the monogenean trematode of the' genus Diplozoon. Examination of 2-month-old fry, collected on August 10, 1976, revealed a 20 % extensity of 1 adult worm or larva. Examination performed one month later (September 6, 1976), however, showed an extensity of 70 % and intensity of 2.5 worms. The maximum invasion intensity found was 7 parasites. The study presents the species determination of the material gathered from the gills of the invaded fish fry. The metrical characteristics of the trematode are as follows: total length 2.6-3.1 mm, length of the anterior part of the body 1.7 to 2.08 mm, the posterior part was 0.78 -1.4 mm long. The ratio of the anterior and posterior parts was 2-2.17: 1. The clamps were 0.099-0.156 mm wide. The handle of the additional hooklets was 0.0410.047 mm long, the hooklet proper was 0.018 to 0.022 mm long, the spike was 0.006 mm long. All specimens belong to the species Diplozoon homoin which is a frequent parasite of several cyprinid fish species (Rutilus rutilus, Carassius carassius, Leuciscus cephalus, Alhurnus alhurnus). Hypophthalmichthys molitrix is a new host of the monogenean trematode Diplozoon homoin. The above-mentioned cyprinid fish present in ponds and supplying water sources should be regarded as reservoirs of the parasite. Gills, parasite, morphology, reservoir fish. Regular examination of health status of herbivorous fish reared in the fish culture unit (State Fishery, Pohoi'elice), performed in 1976, repeatedly revealed mild to heavier infestation of the silver carp fry with the monogenean trematodes of the genus Diplozoon. Materials and Methods The examinations were conducted on silver carp fry from the pond "Mirovy" of the State Fishery, Pohorelice, after artificial spawning made between June 10 and 20, 1976. The fry was transferred into the nursery pond to be grown in monoculture. Prior to stocking, the bottom of the pond was disinfected. The nursery pond was supplied with water from the river Jihlava. There were no barriers or prefiltering so that uncontrolled various fish species were living in the system. The first silver carp fry were fished for parasitological examination on August 10, 1976, the second sampling was done on September 6, 1976 before transfer of the fish into storage ponds. From both fishings, 30 fry were examined for freedom from parasites by means of the complete parasitological dissection. All gill arches were examined thouroughly, the monogenean trematodes of the genus Diplozoon were collected, spread on the glass in one drop of water, gently pressed by the cover slide, fixed in glycerine-alcohol, transferred into clean glycerine. The cover slide was 238 then framed. by varnish. The metrical data presented. in this work were collected. from the fixed. parasites. The infestation was evaluated. in terms of extensity (i. e. percentage of silver carp infested) and intensity (parasite number in individual infested silver carp). Results and Discussion The first collection of silver carp comprised fry about 2-month-old and 36 to 54 mm long (mean 49 mm). Monogenean trematodes of the genus Diplozoon were found in 6 specimens (20 % extensity). Two fish were parasitized by one mature specimen and in 4 fish the larval stages (diporpa) were found. Fig. 1. Diplozoon homoin from the gills of the silver carp (adult individuals grown together) The second fishing (about one month later) revealed almost completely impaired growth of the fry caused by advanced diplostomosis of the eye lens and kryptobiosis of the gills. The fish were 3 months old and only 39-53 mm long (mean 45 mm). The trematodes of the genus Diplozoon were found in 21 specimens (extensity 70 %). Sexually mature parasites were collected from 18 fish (extensity 60 %), larvae were found in 9 fish (extensity 30 %). Five fish were parasitized by both larval and adult trematodes. Maximum intensity with 2 larval and 5 adult flukes was found in one 40 mm long silver carp. In fry with higher invasion intensity invariably one trematode was found on one gill arch, only in one case 2 parasites on one gill arch were detected. The remaining gill arches were free from parasites of this genus. 239 Further examinations of the silver carp fry were made from 1976 to 1979 in several localities of the area and revealed no more parasites of this genus. Results of the parasitological examinations made in 1976 are given in Table 1.

The maximum invasion intensity found was 7 parasites.
The study presents the species determination of the material gathered from the gills of the invaded fish fry.The metrical characteristics of the trematode are as follows: total length 2.6-3.1 mm, length of the anterior part of the body 1.7 to 2.08 mm, the posterior part was 0.78 -1.4 mm long.The ratio of the anterior and posterior parts was 2-2.17: 1.The clamps were 0.099-0.156mm wide.The handle of the additional hooklets was 0.041-0.047mm long, the hooklet proper was 0.018 to 0.022 mm long, the spike was 0.006 mm long.All specimens belong to the species Diplozoon homoin which is a frequent parasite of several cyprinid fish species (Rutilus rutilus, Carassius carassius, Leuciscus cephalus, Alhurnus alhurnus).
Hypophthalmichthys molitrix is a new host of the monogenean trematode Diplozoon homoin.The above-mentioned cyprinid fish present in ponds and supplying water sources should be regarded as reservoirs of the parasite.

Gills, parasite, morphology, reservoir fish.
Regular examination of health status of herbivorous fish reared in the fish culture unit (State Fishery, Pohoi'elice), performed in 1976, repeatedly revealed mild to heavier infestation of the silver carp fry with the monogenean trematodes of the genus Diplozoon.

Materials and Methods
The examinations were conducted on silver carp fry from the pond "Mirovy" of the State Fishery, Pohorelice, after artificial spawning made between June 10 and 20, 1976.The fry was transferred into the nursery pond to be grown in monoculture.Prior to stocking, the bottom of the pond was disinfected.The nursery pond was supplied with water from the river Jihlava.There were no barriers or prefiltering so that uncontrolled various fish species were living in the system.
The first silver carp fry were fished for parasitological examination on August 10, 1976, the second sampling was done on September 6, 1976 before transfer of the fish into storage ponds.
From both fishings, 30 fry were examined for freedom from parasites by means of the complete parasitological dissection.All gill arches were examined thouroughly, the monogenean trematodes of the genus Diplozoon were collected, spread on the glass in one drop of water, gently pressed by the cover slide, fixed in glycerine-alcohol, transferred into clean glycerine.The cover slide was then framed.by varnish.The metrical data presented.in this work were collected.from the fixed.parasites.
The infestation was evaluated.in terms of extensity (i.e. percentage of silver carp infested) and intensity (parasite number in individual infested silver carp).

Results and Discussion
The first collection of silver carp comprised fry about 2-month-old and 36 to 54 mm long (mean 49 mm).Monogenean trematodes of the genus Diplozoon were found in 6 specimens (20 % extensity).Two fish were parasitized by one mature specimen and in 4 fish the larval stages (diporpa) were found.The second fishing (about one month later) revealed almost completely impaired growth of the fry caused by advanced diplostomosis of the eye lens and kryptobiosis of the gills.The fish were 3 months old and only 39-53 mm long (mean 45 mm).The trematodes of the genus Diplozoon were found in 21 specimens (extensity 70 %).Sexually mature parasites were collected from 18 fish (extensity 60 %), larvae were found in 9 fish (extensity 30 %).Five fish were parasitized by both larval and adult trematodes.Maximum intensity with 2 larval and 5 adult flukes was found in one 40 mm long silver carp.In fry with higher invasion intensity invariably one trematode was found on one gill arch, only in one case 2 parasites on one gill arch were detected.The remaining gill arches were free from parasites of this genus.
Further examinations of the silver carp fry were made from 1976 to 1979 in several localities of the area and revealed no more parasites of this genus.
Results of the parasitological examinations made in 1976 are given in Table 1.Species determination of the collected parasites was done according to the criteria presently used for the genus Diplozoon (pejcoch 1968).
The body of the adult trematode was 2.6-3.1 mm long, with maximum width of 0.65-1.3mm, width of the haptor was 0.5 to 0.6 mm.The anterior part of the body was 1.7-2.08mm long and 0.65-1.3mm wide.The posterior part was 0.78-1.4mmlong and 0.39 to 0.7 mm wide.The ratio between the anterior and posterior parts of the body was 2-2.17: 1. Dimensions of the oral suckers were 0.049 x 0.059-0.66mm,those of the oval pharynx 0.046-0.049x 0.066-0.067mm.
The intestine had numerous branches sent off in its course and they were extremely deep.The caudal end of the intestine was not very clear in our fixed specimens.The reprodactive tract was placed in the caudal part of the body which was folded just behind the junction.There were usually 11 to 12 folds.
The haptor was equipped with metamorphosed clamps of usual shape.The first pair of clamps was 0.099 to 0.115 mm wide the second pair was 0.117-0.140mm wide, the third reached 0.125-0.148mm, and the fourth pair was 0.125-0.156mm wide.
The handles of the hooklets situated between the clamps was were 0.041-0.047mm long, the hooklets proper wereO.018-0.022mmlong,and the spikes were 0.006 mm long.
We give no description of the sexually mature in.:.dividual, its dimensions are presented in  "disc", 1.3-2.1 mm in diameter.The size of the parasite and the handle of the hooklets (0.058-0.060 mm) surpass several times that of our specimens.
The species Diplozoon marinae is described in detail by Achmerov (1974) and our specimens do not differ from this description except for the length of the handle of the hooklets which was invariably longer in our material.Maximum length of the handle described by Achmerov (1974) reached only the sizes found in the smallest individuals of our collection.However, the hooklet proper was found to be twice as long as that described by the above-mentioned author.
Although according to Er gens and L om (1970) the majority of determination cri- Several species of the genus Diplozoon have been found in fish from the river Danube (Pej eoch 1968).Among these, the species D. homoin seems to be the dosest to our specimens in terms of dimensions.This conclusion is also supported by data of B y-   (1962), who found sizes of the handles of hooklets similar to those found in our specimens.
On the basis of our findings and data of other authors it seems correct to classify the investigated specimens as Diplozoon homoin.
Moreover, our study indicates that a detailed zoological elaboration of parasites found in acclimatized herbivorous fish is of great importance in that it may prevent incorrect conclusions concerning transmission of parasites from the basin of the river Amur or some other areas with fish importation.
The study has further shown that the monogenean trematode Diplozoon homoin parasitizing in Rutilus rutilus, Carassius carassius, Leuciscus cephalus and Alhurnus alhurnus has been repeatedly found also in fish from the river basin of South Moravia.However, the definitive host of the parasite is the silver carp.Only in this fish species the sexual maturation of the trematode occurs.The above--mentioned hosts of the trematode are frequent weed fish species also under fish farming conditions and they should be considered as reservoirs of the trematode for the silver carp.This herbivorous fish belongs to economically important species to which intensive veterinary care is given.U vzorkli odebranych 10.VIII.1976, asi dva mesice po narozeni ryb, byla zjistena extenzita vyskytu 20 %, pri intenzite 1 dospely eerv nebo larva u jedne ryby, u vzorku odebraneho 6. IX. 1976 stoupla extenzita invazi na 70 %, pri prlimeme intenzite 2,5 eerva.Maximalni intenzita byla 7 eervli.Studie se zabyva druhovou determinaci dokladoveho materialu s pouiitim soueasne platnych kriterii pro druhove rozlisovani ptislusnikli tohoto rodu.

Fig. 1 .
Fig. 1.Diplozoon homoin from the gills of the silver carp (adult individuals grown together)