PARASITOSES IN THE FRY OF SELECTED FRESHWATER FISH SPECIES UNDER THE CONDmONS OF STRIPPING AND REARING

Navratil S.: Parasitoses in the Fry of Selected Freshwater Fish Species under the Conditions of Stripping and Rearing. Acta vet. Bmo. 60. 1991: 357-366. During the period from 1984 to 1989. the problem of parasitic invasion into the artificially reproduced and reared fry of the freshwater fish species (Barbus barbus, Chondrostoma nasus. Leuciscus cephalus, Aspius aspius) wereinvestigated at a specialized fish breeding farm ofthe Czech Angler's Union in Tfeb1C!-PouSov situated on the river Jihlava (the Danube river basin). The invasion with parasites was investigated in 979 fish specimens (846 juvenile. 133 adult) of the selected species and in 257 fish of other species. The reared fry of the selected fish species were found to be' endangered already in their first days ofHfe. predominantly by ectoparasitic protozoa with not definitely formed host specificity. Thus optimal rearing conditions have to be assured. along with regular examination of the health status. Efficient preventive antiparasitic baths have to be applied. It is advantagenous to complement these measures with an effective way of sanitation of the fish-rearing farms. by the investigation of the health status of fish in the feeder of the fish-hatchery and rearing pond with its regulated stocking, . or possibly by declaring relevant areas as being protected with the introduction of a closed turnover of the parent fish shoal. Barbus barbus. Chondrostoma nasus. Leuciscus cephalus. Aspius aspius. ectoparasitic protozoa. zoooeterinary measures . The industrial development. intensification in agriculture and the growth of residential areas are the principal sources of water pollution. The living conditions in water courses have changed in recent years due to waste water discharge, run-offs from surface drainage, the increase of eutrophisation, acid rain, and water course regulation. This caused that some of the fish species have lost their viability in these waters, and in other the fish-planting cannot be ensured by a natural reproduction. It has thus been necessary to proceed to artificial stripping. rearing and planting of these fish species. This concerns also the investigated fish species (barbel Barbus barbus. nase Chondrostoma nasus, chub Leuciscus cephalus and asp Aspius aspius). The introduction of the above mentioned modem technologies of reproduction and rearing results in new problems concerning the health status of fish. Technological processes of stripping and rearing of fry for the fish species mentioned above have been worked out only recently but in some cases they are still missing. During our investigation only the methods of stripping and rearing for the barbel species were available in a complete form applicable for our fishery (Krupka 1987). Pecha (1986) reported on his experience with stripping and rearing of the asp. The method of artificial stripping and rearing of the investigated species is thus based on the procedures worked out for other fish species and on the experience of hatcherymen and breeders. The success of stripping and rearing, with the smallest possible health problems and losses

The industrial development.intensification in agriculture and the growth of residential areas are the principal sources of water pollution.The living conditions in water courses have changed in recent years due to waste water discharge, run-offs from surface drainage, the increase of eutrophisation, acid rain, and water course regulation.This caused that some of the fish species have lost their viability in these waters, and in other the fish-planting cannot be ensured by a natural reproduction.It has thus been necessary to proceed to artificial stripping.rearing and planting of these fish species.This concerns also the investigated fish species (barbel -Barbus barbus.nase -Chondrostoma nasus, chub -Leuciscus cephalus and asp -Aspius aspius).The introduction of the above mentioned modem technologies of reproduction and rearing results in new problems concerning the health status of fish.
Technological processes of stripping and rearing of fry for the fish species mentioned above have been worked out only recently but in some cases they are still missing.During our investigation only the methods of stripping and rearing for the barbel species were available in a complete form applicable for our fishery (Krupka 1987).Pecha (1986) reported on his experience with stripping and rearing of the asp.The method of artificial stripping and rearing of the investigated species is thus based on the procedures worked out for other fish species and on the experience of hatcherymen and breeders.
The success of stripping and rearing, with the smallest possible health problems and losses of the reared fry, is dependent upon many circumstances participating more or less in the development of good health condition of the fry.These circumstances have been presented to various extent in almost all surveys concerned with fish diseases (e.g.Bauer et al. 1983;Dyk 1961;Lucky 1986a, b;Schiiperc1aus et al. 1979).The spawn incubation should not be affected by unexpected events provided that established technological procedures are observed when manipulating with the spawn.A certain danger is seen in saprolegniosis of the spawn that can, however, be suppressed by the use of suitable control baths (Krupka 1987;Lucky and Navratil 1986).The health status of the hatched fry is affected by some external factors, predominantly by the quality of water, its temperature and by the supplementary feeding (Jirhek 1980;Lucky and NavdtilI986).Protozoan ectoparasitoses represent the highest danger occurring during the early stages of fry rearing.The seriousness of this is seen in a possibility of a rapid spread of this disease in accumulated rearing and stocking followed by a: high, or even total death rate (Koufil et al. 1984).The prevention of causal agent invasion, disinfection of rearing equipment, of implements and tools, provision of harmless water sources and supplement feed represent important control measures (Krupka 1987).Prophylaxis and therapy are carried out by various types of baths or applying a premedicated feed (Koufil et al. 1984;Lucky 1986a;Schiiperclaus et al. 1979).
Both home and foreign literature is abundant in data concerning parasitic fauna of the investigated fish species or parasites invading them.These works concern mostly the fauna and zoology without more detailed pathogenetic and pathologic analyses (e.g.Bychovskij et al. 1962;Brgens and Lom 1970;Gusev et al. 1985;Ivasik 1963;Lom, Dykova et al. 1989;Markevitch 1951;Molnar 1964Molnar , 1968Molnar , 1969Molnar , 1970;;Moravec 1971;Pellerdy and Molnar 1968;Plehn 1924;Shulman et al. 1984;Vojtek 1974;Vojtek, Folkmanova and Brgens 1954;ZitIian 1960).From the presented and many other literature sources follows that apart from parasitic protozoa with not definitely formed host specificity which can parasitize on any fish host, the barbel can be invaded by more than 70 species of parasites, the nase by 60 species, the chub by almost 120 species and the asp by almost 90 species of parasites.Most of these parasitic species can be found in our country or in the river basins of our area; thus, there exists a real possibility of the fish invasion by these parasites.
The aim of the present work was to define parasitoses endangering the fry of the investigated non-traditional fish species under particular conditions in the fish-breeding farm of the Czech Angler's Union at Tfebfc-Pou §ov and possibly to define a character of their development and to find suitable veterinary measures to prevent the appearance of parasitoses or to find a way of combatting them.

Materials and Methods
The investigated fish-breeding farm, Fish Hatchery MO CSR Tfebic-Pousov, belongs to the Czech Angler's Union and rears fish for its own'use.The establishement was builtin 1980, is situated in the valley ofthe Jihlava river (the Danube basin) in its barbel zone, the altitude being 425 m.It takes up an area of 3.8 hectars.In the farm, the stripping and rearing of Barbus barbus, Chondrostoma nasus, Leuciscus cephalus, Aspius aspius, Salmo trutta, Thymallus thymallus, Stizostedion lucioperca, Lota Iota and possibly of other fish species are conducted.
Fertilized and, if need be, deglutinized eggs of the investigated fish species are incubated in hatchery vessels with the bottom water feed until they hatch.The hatched fry are then reared in hatchery instruments.Later they are transferred into little ditch ponds with sufficient natural food.The stock density ranges from 200 to 500 per mS.In these ditch ponds the fry stay up to the age of 8-12 weeks, then they are caught and dispatched to individual fishery organizations.Fingerlings are then reared in smaller ponds or planted directly into free water.After transferring the fry the ditch ponds are emptied and wintered.In case of necessity the preventive long-term baths in malachite green are carried out more or less regularly (approximately once in a week) over the period of fry rearing.
The investigated fish can be divided into several groups.The first group was represented by adult fish of the examined species caught in spawning sites at various localities of the Jihlava river, or at other Southern Moravia localities.The second group included fry of these fish that were examined in more or less regular intervals from hatching to the expedition and planting into natural conditions.The fry were obtained directly at the investigated fish-breeding farm and, in very few cases, also at other farms to which they had been transferred.Since many of the invasive agents of fish diseases do not posses a specific affinity to particular fish species, and farms where stripping and rearing are carried out are often supplied with water from stocked streams, attention has been paid also to other fish species.The latter originated directly from the same investigated farm; ~tream over the farm, or localities from where the parent fish were obtained.
The fish were examined in a native form and in some cases, in order to obtain a complete determination of protozoa and their stage of development, a certain number of samples was fixed in 4 % formaldehyde for later processing by histological methods.
Methodical procedures were chosen to obtain the Vlost complete data on the spectrum of the agents of invasive diseases, their pathological effect and possibly of other ill-health and were based on procedures recommended by Ergens andLom (1970) andLucky (1982).
The found parasites were immediately determined and isolated, fixed and preserved in a suitable way for a later precise determination.The methOds used were based on procedures described in literature (Ergens and Lom 1970;Lucky 1982;Musselius et aI. 1983;Schiiperclaus et a!. 1979).The actual determination was carried out according to various keys of determination (Bychovskij et aI. 1962;Ergens and Lom 1970;Gusev et aI. 1985;Lucky 1982;Shulman et al. 1984).The prevalence of the parasitic invasions was expressed in per cents of invaded fish in individual samples, their intensity by the number of protozoa found in a microscopical field at a certain-magnification or by an absolute number (see Tables).
f.In juvenile Leuciscus cephalus fish (Table 3) 8 species of parasites were isolated, all of them being protozoa (Ichthyobodo necator, Myxobolus pseudodispar, Chilodonella piscicola, Ichthyophthirius multiftliis, Epistylis lwoffi, Apiosoma piscicola, Trichodina pediculus, Tripartiella copiosa).Greater losses were not, however, found.It should also be pointed out that skin chilodonellosis, being observed in: its early stages in two-week old fish, was not found in adult fish.This can be ascribed to the effect of control measures.1.,..60 0-1/32 X • 1-6 0-1/100X 0-1/32x 0-8/32 X 0-3/32 X 0-12/32 x 0-1/32x 0-3/32 x 0-100/32x g. Seven parasite species were isolated in juvenile Aspius aspius (Table 4), out of them 5 protozoan species (Ichthyobodo necator, Ichthyophthirius multifiliis, Apiosoma piscicola, Epistylis lwoffi, Trichodina nigra), 1 trematode metacercariae (Cotylurus pileatus) and 1 roundworm species in a larval stage.Parasitic invasions were observed already in two-week old fish.Losses caused by invasive diseases were not found, although the incidence of several of them (Apiosoma piscicola and Trichodina nigra in skin, Cotylurus pileatus in body cavity) was high and reached as much as 80-96.6 %.Attention should be paid to the fact that the extensive invasion of Trichodina nigra ill two-week old fish was not observed in five-and six-week old ones which can again be explained by the efficacy of control measures.The ease with which the parasitic fauna can be imported and enriched with other species, if the veterinary inspection is not carried out, can be shown on the case of imported Aspius aspius from Hungary.All these protozoa were also found in the fry of the investigated fish.This confirms a general spread of these parasites in the investigated fish-breeding farm.

Discussion
The findings of parasites in adult barbels correspond in most cases to the literature data on the parasite spectrum in Barbus barbus and of their spread, our country and their localisation in hosts.Cysts ofthe-Myxobolus branchialis sporozoon were found very frequently in gills of adult barbels coming from various areas on the Jihlava river although Ergens and Lom (1970) regard M. branchialis to be a relatively rare parasite of B:zrbus barbus in the Danube basin.Taking into account the literature data (Shulman et al. 1984), the finding of Myxobolus cyprini cysts in bulbus arteriosus and in kidneys of barbels coming from the Ivancice area on the Jihlava river is unusual.The authors report that a whole series of carp fish (31) can serve as hosts to M. cyprini but the barbel is not included.This finding thus expands the so far known spectrum of hosts of this parasite.The broadening of the host spectrum concerns also the isolation of Trichodina fultoni on skin and gills and of Tripartiella copiosa on gills.The isolation of small formations reminding of eggs of the blood fluke (Sanguinicola sp;) in internal organs (mostly in liver and kidneys) and on the gills of adult barbels appears to be very frequent.With regard to the scarce literature data on this parasite in Barbus barbus it is very interesting.These formations obstructed blood vessels and caused circulation disorders (Fig. 1).
As it was already presented in the Results section mostly protozoan parasites with not well pronounced host specificity were found in juvenile barbels.The same applies also to Epistylis, Trichodina acuta, Trichodina nigra and Tripartiella copiosa.The barbel is not~however, reported in literature as being a host of these parasites (Ergens and Lom 1970;et al. 1989;Shulman et al. 1934).Due to the occurrence in our area and a relatively broad sp~ctrum of the mentioned hosts the observed invasions cannot be regarded as unusual but we have to consider them as broadening the host spectrum.The isolation of adult monogenea of Dactylogyrus vastator in an uncommon host, in Barbus barbus, appears to be very interesting.Gusev et al. (1985) refer to Carassius carassium, C. auratus gibelio, Cyprinus carpio and C. carpio haematophterus as being hosts of this parasite.The presence in other hosts was observed by e.g.KaSilik (1956) in Vimba vimba.Also Gusev et al. (1985) report on similar cases.The level of the observed invasion was, however, so low that it had not affected the health condition of the reared stock.Dactylogyrus vastator could have got into the rearing ditch ponds through tributary water or fishing gear.At the time of the isolation, carp stock that could possibly be infected with the parasite was reared on the premises.The possibility of mistaking this parasite for Dactylo!!yrus crassus was excluded by morphological examination ofisolated specimens and comparison with literature data presented by Gusev et al. (1985).
Similarly as in the case of adult barbels, the spectrum of parasites found in adult nase corresponded to that presented in most literature information on the parasite spectrum and their spread in our area and their localisation in a host.The only exception was the isolation of Ambiphrya sp. on the skin, nostrils and on the gills of parent nases.Since the observed morphological finding did not correspond with any described species of Ambiphrya (Shulman et al. 1984) the parasites were simply denoted as Ambiphrya sp. (Fig. 2).The nase is not presented in literature as being a host of Epistylis lwoffi, Trichodina pediculus, Tripartiella copiosa.With regard to the occurrence of these parasites in our area and to a relatively broad spectrum of their hosts their isolation in Chondrostoma nasus cannot be considered unusual but as broadening the host spectrum.
The observed parasitic fauna of juvenile nases was represented by ectoparasitic protozoa with only slightly pronounced specificity.Ambiphrya sp., Epistylis lwoffi, Trichodina pediculus and Tripartiella copiosa were among species isolated in Chondrostoma nasus and their occurrence was discussed previously.
Similarly as in adult fish of the preceding species, the finding of parasites in adult chubs corresponded in most cases to literature data on the spectrum of parasites and their spread in our area, and their localisation in the host.The final determination of flagellates of Trypanosoma sp. could not be carried out due to the poor quality of the stained preparation.Although the Leuciscus cephalus sp.have not been presented in literature as a host of Trichodina fultoni the finding cannot be considered as unusual.The broad host spectrum, as presented e.g. by Shulman et al. (1984) confirms the only slightly pronounced host specificity.
The parasitic fauna of the eXamined juvenile chubs consisted mostly of ectoparasitic protozoa.Although in case of Epistylis lwoffi the Leuciscus cephalm' is not reported as being a host Shulman et al. (1984) admit a relatively broad spectrum of hosts and our findings correspond with this opinion.
The parasitic fauna of juvenile asps also consisted mostly of ectoparasitic protozoa and their occurrence and localisation in hosts were not contradictory with the literature data.In literature presented host spectrum of these parasites is so broad that their occurrence in Aspius aspius cannot be considered as surprising.The isolation of metacercariae Cotylurus pileatus in the body cavity of imported Aspius aspius from Hungary cannot be regarded as unusual.The pathogenicity of the observed invasion is difficult to assess.The fact is that the death of fish not observed and the nutriture was also found to be good.A relatively high prevalence of the invasion confirms that the imported fish Came from areas with a higher concentration of gulls -definite hosts -and at the same time from areas where first intermediate hosts occur.The only finding of the roundworm larva in the body cavity of juvenile asp cannot be considered as too important from the fish health point of view.
All parasites found in other adult fish belonged to the group of commonly' occurring parasites with only slightly pronounced host specificity as reported: in various literature data (e.g.Bychovskij et al. 1962;Ergens and Lom 1970;Shulman etal. 1984;Vojtek 1974).Two species of protozoa (Ichthyophthirius multifiliis and Trichodinella epizootica) were isolated also in the fry of the fish studied in more detail.The parasites found did not affect the health of fish.
Most of the parasites isolated in the fry of other fish reared in the fish-breeding farm at Tiebfc-Pou.~ov were found also in the fry of the investigated fish species.It confirms a common spread of these parasites in the surveyed fish-rearing farm~ The fry of the investigated fish species obtained by stripping is endangered particularly by ectoparasitic protozoa with not well pronounced host specificity already in the first weeks of life.Good level of feeding and zoohygienic conditions together with the preventive antiparasitic baths in malachite green were adequate to maintain good health status of the fry of the investigated fish, without greater losses in stock and without the risk of spreading the invasive diseases.
In many fish-breeding farms the incorporation of .aethiologicalagents,e.g. with tributary water or fishing gear (it applies fully to the investigated fish-breeding farm) cannot be excluded.Thus, it is necessary to provide good conditions of breeding (ample natural food, convenient temperature of water and its chemism); regular examination of health of the fish and subsequent efficient preventive anti ... parasitic baths .. Also, it is necessary to prevent the uncontrolled import of the fry and stock fish from abroad.The presented measures, based directly on the results of investigation, should be complemented by an efficient sanitation of rearing premises after the hatching and rearing were finished, by a permanent examination of the health status of fish in the hatchery and rearing farm with their controlled stocking, or by declaring a veterinary protection area and introducing "all in all out" system for parent fish.Odchovavany pllidek sledovanych druhli ryb byl jiZ v prvnich tjdnech zivota ohrozovan pfedevsim ektoparazitickjmi prvoky s nepillis vyhranenou hostitelskou specifienostf.

Table ' 3
Paruites of Juveui1e Leuc1scus CepbalU8 Thus, in the reared fry of the investigated fish two parasite species were observed (Ichthyophthirius multifilliis, Trichodinella epizootica), these being found also in adult fish of other species in the above mentioned localities.The health status of the adult fish of other species was found to be good.