Diplozoon Paradoxum Research Articles

Assessment of ecto and endo parasites of Schizothorax plagiostomus inhabiting river Panjkora, Khyber Pakhtunkhwa, Pakistan.

Fish provides main source of high quality protein to more than one billion people in the world. Fish parasites directly affect the productivity of fish and indirectly on human health. This research was aimed to assess the helminth parasites in Schizothorax plagiostomus (the snow trout) from river Panjkora, KP, Pakistan. A total of 88 fish samples (n= 88) were collected from the upper, middle and lower regions of the river through cast nets, hand nets and hooks. All the collected fish samples were examined in the Parasitology Laboratory, Department of Zoology, University of Malakand for helminth parasites during July 2018 to February 2019.Among these fishes nematodes, trematodes, cestodes and acanthocephalan were isolated and identified. Overall prevalence of the fish parasites was 60.22% (53/88). The intensity of the parasite was observed from 1.7% to 4.61%. Highest prevalence was reported in summer season 86.36% while lowest in the winter season 36.36%. This study shows that summer season affects the fish business and result in poor quality fish meat with risk of zoonotic diseases. Adults were highly infected 82.25% while no infection was found in juvenile specimens. Female fish samples had higher prevalence 68.22% than males 48.22%. Fishes of the lower reaches had highest prevalence 60.22% than the upper reaches 40.0%. Fish samples with maximum length and weight were highly 76.92% infected than small sized fish with low body weight. Present study addresses that Rhabdochona schizothoracis in the intestine and Diplozoon paradoxum in gills of snow trout fish has a long term relationship and call as a natural infection in cyprinids and it is zoonotic threat to human.

State of the organism of the same year scaly carp infected by Eudiplozoon nipponicum

One of the least studied monogeneses doses, for today, there is diplopic zoonosis of carp. Previously, it was believed that there is only one fish parasitize bothrium – Diplozoon paradoxum. However, in recent years it has been discovered and described already more than 10 species of pathogens of diplozoons, in particular Eudiplozoon nipponicum. Outbreaks of this disease are increasingly beginning to be recorded in fish ponds farms of the western region of Ukraine. Moreover, more often than in others in the amount of this parasite occurs in young fish. In view of the above, the purpose of our research was to investigate the degree of infestation of the same year scaly carp with the mentioned ectoparasite and study the changes that occur in morphological and biochemical composition of blood, intensity of peroxide processes, as well as the state of antioxidant and immune systems in invasive fish. The research was carried out in the garden and fish farms of the State Enterprise “Rybhosp"Galitskyi” (renamed LLC “Rybgosp “Burshtynskyi”) Ivano-Frankivsk region and FG “Dobrotvir fish factory” of Lviv region with the same year scaly carp. Two experiments were selected for the experiment groups of the same yaer of scaly carp (control – non-invasive fish and experimental – invasive with Eudiplozoon nipponicum) in 6 specimens of fish in each group of weights bodies 45–47 g. In experimental fish they were studied their infestation with ectoparasites, as well hematological parameters, protein content of the blood, peroxide intensity processes, the state of antioxidant and immune systems of non-invasive and invasive specimens. During the parasitological examination of both experimental fish farms was detected infestation in scaly carp caused by ectoparasites Epidipalous nipponicum. In May there was a pick of infected the same year scaly carps (2.87 and 3.10 eggs/fish). Infected fish, compared to non-invasive fish, there were significant changes in hematological parameters. In particular, in the blood of parasites affected by fish the number of erythrocytes decreased (P < 0.001), the hemoglobin content (P < 0.001) and hematocrit and increased number of leucocyte (P < 0.001).The infected scaly carp the above-mentioned parasite pressed by the protein-synthesizing function of the organism, as indicated a high (P < 0.001) reduction in total protein, albumin and α-globulins in the blood serum, there is a depression in them humoral links of non-specific resistance and antioxidant system activity protection, and the content of products of peroxide oxidation of lipids in their hepatopancreas significantly increases.

New location, food composition, and parasitic fauna of the invasive fish Pseudorasbora parva (Temminck & Schlegel, 1846) (Cyprinidae) in Poland

Stone moroko ( Pseudorasbora parva ) is considered to be one of the most invasive fishes, dispersing rapidly all over Europe and also in the freshwaters of the Baltic Sea basin. A recent survey carried out in the catchment of the lower part of the Odra River (Poland) in 2015 and 2016 revealed a large new population of stone moroko, which had colonized the creek Wardynka. The sample of 518 fish caught was dominated by age groups 1+ (341 specimens) and 2+ (99 specimens); however, older fish were also present, which means that at the moment of analysis the species had been in the Wardynka for at least 5 years. The diet was composed of copepods, amphipods, ostracods, and cladocerans, with Daphnia sp. being most frequent, which also showed the highest index of relative importance and percentage by weight in the food. The parasitic fauna composition of stone moroko in the new location involves local parasites only. Trichodinella subtilis, Diplozoon paradoxum, Apatemon gracilis , and Caryophyllaeus laticeps were found for the first time ever. The lack of parasitic species that normally occur in fish of this species was probably caused by the lack of intermediate hosts, which are necessary to complete their life cycles.

Excretory system of representatives from family Diplozoidae (Monogenea).

Diplozoons are representatives of blood-feeding ectoparasites from the family Diplozoidae (Polyopisthocotylea, Monogenea). Although these worms have been the subject of numerous taxonomical, phylogenetic, and ecological studies, the detailed study of their excretory system has remained relatively neglected. Our observations focused on the morphological and ultrastructural features of the excretory apparatus of four diplozoid species: Diplozoon paradoxum, Eudiplozoon nipponicum, Paradiplozoon bliccae, and Paradiplozoon homoion. Observations were obtained using two microscope methods: light microscopy, equipped with differential interference contrast (Nomarski DIC) and transmission electron microscopy (TEM). The ultrastructure of two basic compartments which forms the excretory apparatus, flame cells with filtration apparatus, and canal cells forming the protonephridial ducts is revealed in this study. A unique consecutive sequence of longitudinal semi-thin sections of the excretory pore of E. nipponicum is visualized there for the first time.

Aspects of the morphology of the juvenile life stages of Paradiplozoon ichthyoxanthon Avenant-Oldewage, 2013 (Monogenea: Diplozoidae)

There are eight life stages in the life-cycle of Diplozoon paradoxum and limited knowledge of the life-cycle for other diplozoid genera exists. The aim of this study was to record the number of life-stages of Paradiplozoon ichthyoxanthon obtained from, Labeobarbus aeneus and Labeobarbus kimberlyensis, in the Vaal Dam from 2005 to 2007. Six larval life stages and one adult stage of P. ichtyoxanthon were identified from specimens collected in vitro and in situ. In vitro, eggs hatched after 21 days at 18°C. Eggs collected during winter were significantly larger than those laid during spring or summer. Paradiplozoon ichthyoxanthon oncomiracidia have peripheral eyes with pink pigmentation, a tubular anterior bladder-like structure, bicuspid basal pharynx valve and a branched digestive caecum and residual shell material or vitellaria in the caecum. Immature reproductive tissue connected to the ventral sucker and dorsal papillae were noted for the first time in diporpa. Large nervous ganglia and innervation of muscle were observed around the ventral sucker.

Attachment ability of a clamp-bearing fish parasite, Diplozoon paradoxum (Monogenea) on gills of the common bream Abramis brama

Monogeneans, which are mainly fish ectoparasites, use various types of haptoral (posterior) attachment apparatus to secure their attachment onto their hosts. However, it remains unclear how strongly a monogenean can attach onto its host. In the present study, we aimed for the first time to (1) measure pull-off forces required to detach a pair of clamp-bearing monogeneans, Diplozoon paradoxum, from gills of Abramis brama and (2) determine the contribution of muscles to the clamp movements. A mean force of 6.1±2.7 mN (~246 times the animals' weight) was required to dislodge a paired D. paradoxum vertically from the gills. There were significant differences (P<0.05, Tukey test) between the widths of clamp openings in D. paradoxum treated in three different solutions: the widest clamp openings were observed in the monogeneans treated in 100 mmol l(-1) potassium chloride solution (58.26±13.44 μm), followed by those treated in 20 mmol l(-1) magnesium chloride solution (37.91±7.58 μm), and finally those treated in filtered lake water (20.16±8.63 μm). This suggests that the closing of the clamps is probably not due to the continuous contraction of extrinsic muscles but is caused by the elasticity of the clamp material and that muscle activity is required for clamp opening.

Metazoan parasites of Alburnus chalcoides in Tödürge Lake (Zara/Sivas, Turkey)

Summary The metazoan parasites of the Danube bleak, Alburnus chalcoides (Guldenstadt, 1772), were determined in Todurge Lake, since the parasite fish fauna had not yet been studied in this system. A total of 106 specimens were collected from October 2004 to September 2005. Six parasite species were found: two monogeneans (Diplozoon paradoxum and Diplozoon megan), one digenean (Posthodiplostomum cuticola), one cestode (Bothriocephalus acheilognathi), one nematod (Rhabdochona sp.), and one copepod (Argulus foliaceus). About 87.7% of the Danube bleak examined were infected by at least one parasite: Rhabdochona sp. (4080 specimens), Posthodiplostomum cuticola (312 specimens) and Diplozoon megan (159 specimens) being the dominant parasites. Only 33% of the fish carried one parasitic species whilst the remainder had two (21.7%), three (17.9%) and four different species (15.1%). The frequency of infestation changed according to seasonal conditions, with a maximum 94.3% observed in spring. Occurrence, density, seasonal changes, and preferences of the parasites species for various ages and size groups of the bleak were identified, despite the limited overall sample size. D. paradoxum, D. megan, P. cuticola, B. acheilognathi, Rhabdochona sp. and A. foliaceus were determined for the first time as parasites of Danube bleak in Turkey. D. megan was also a new record for the fish parasite fauna of Turkey.

Comparative karyological analysis of four diplozoid species (Monogenea, Diplozoidae), gill parasites of cyprinid fishes

The present study has revealed new data on chromosome complements of diplozoid parasites, namely Diplozoon paradoxum from freshwater bream Abramis brama, Paradiplozoon bliccae from white bream Blicca bjoerkna, Paradiplozoon sapae from white-eye bream Ballerus sapa, and Paradiplozoon nagibinae from zope Ballerus ballerus. Particularly, D. paradoxum is characterized by four pairs (2n=8) of long (up to 22.1 μm) chromosomes: pairs 1, 2, and 3 are metacentric and pair 4 acrocentric. Karyotypes of three Paradiplozoon species are nearly identical in number and morphological classification of chromosomes, each comprising diploid number of 14 one-armed chromosomes of very similar length ranging up to 12.5 μm in P. bliccae, 9.2 μm in P. sapae, and 9.9 μm in P. nagibinae. All four species are similar in their total complement length, ranging from 64.4 to 50.4 μm. Interspecific differences were found in location of secondary constriction: it is situated on short arm of the 1st chromosome pair in D. paradoxum, on long arm of the 7th pair in P. bliccae and on long arm of the 4th pairs in P. sapae and P. nagibinae. Phylogenetic interrelationship within the diplozoids and hypothetic karyotype evolution is here discussed.

The parasite community of the nase Chondrostoma nasus (L. 1758) from Austrian rivers

Between April 2003 and November 2006 a total of 191 individuals of the predominantly herbivorous fish species nase Chondrostoma nasus (L. 1758) were examined for parasites from six river sites in Austria. The following parasite taxa were recovered--Ciliata: Trichodina sp., Chilodonella piscicola, Ichthyophthirius multifiliis; Myxozoa: Myxobolus muelleri (cysts) and Myxobolus sp. (cysts); Monogenea: Dactylogyrus vistulae, D. chondrostomi and Dactylogyrus spp., Gyrodactylus sp., Diplozoon paradoxum; Digenea: Diplostomum spathaceum (larv.) and Tylodelphis clavata (larv.); Cestoda: Caryophyllaeus laticeps; Acanthocephala: Pomphorhynchus laevis; Bivalvia: Unio sp. (Glochidia); Crustacea: Lamproglena pulchella; Hirudinea: Piscicola geometra. The only taxa occurring at all sample sites were Dactylogyrus spp., which was also the dominant taxon at most sites, and Myxobolus muelleri, both from the gills of the fish. This is the first record of the parasite community of the nase in Austria.

Monogenean Trematods—Parasites of Some Cyprinid Fishes from Lakes Ohrid and Prespa (Macedonia)

ABSTRACTDuring parasitological investigations of the gills of 3 cyprinid species from lakes from the Adriatic river basin of Macedonia (Lake Ohrid and Lake Prespa), 7 monogenean species were found: in Chondrostoma nasus we found: Dactylogyrus elegantis, D. vistulae and Paradiplozoon homoion homoion, in Alburnus alburnus we found Dactylogyrus alatus f. typica, Dactylogyrus minor, Diplozoon paradoxum and Paradiplozoon alburni, in Alburnoides bipunctatus we found Dactylogyrus alatus f. typica and Paradiplozoon alburni. Prevalence in Chondrostoma nasus ohridanus is 50,0%, in Chondrostoma nasus prespensis is 41,59% (in total Chondrostoma nasus - 41,88%), in Alburnus alburnus ohridanus is 47,75%, in Alburnus alburnus prespensis is 41,38% % (in total Alburnus alburnus - 44,95%), in Alburnoides bipunctatus ohridanus is 35,14%), in Alburnoides bipunctatus prespensis is 11,54% (in total Alburnoides bipunctatus - 29,0%). The most frequent monogeneans found in the fishes from both lakes are: Dactylogyrus alatus f. typica (established in 17,62% of all examined fishes) and Dactylogyrus minor (established in 16,31% of all fishes). Dactylogyrus alatus f. typica, D. minor, Diplozoon paradoxum and Paradiplozoon alburni represents a first record for the parasite fauna of fishes in Macedonia. The greatest pathological influence is associated with the monogeneans: Dactylogyrus vistulae, Paradiplozoon homoion homoion, Paradiplozoon alburn and Diplozoon paradoxum.

Parasites of carp bream, Abramis brama, from Lake Jamno, Poland

Abstract A total of 40 carp bream, Abramis brama (L.) from Lake Jamno were examined for their parasites in May 2002. Lake Jamno is a brackish-water coastal lagoon, strongly eutrophied and polluted by communal and industrial sewage from the city of Koszalin. The survey yielded 15 parasite species, representing different systematic groups, including 7 monogeneans Dactylogyrus auriculatus, D. falcatus, D. wunderi, D. zandti, Gyrodactylus elegans, Gyrodactylus sp., Diplozoon paradoxum; 4 digeneans (at the stage of metacercaria) Diplostomum sp., Tylodelphys clavata, Ichthyocotylurus platycephalus, I. variegatus; 1 cestode Caryophyllaeus laticeps; 2 crustaceans Ergasilus sieboldi, Argulus foliaceus; and 1 hirudinean Caspiobdella fadejewi. Monogeneans constituted the most abundant parasite group, accounting for 61.5 % of all parasite individuals collected. They were followed by the cestodes (20.7 %), digenean flukes (16 %), crustaceans (0.7 %), and leeches (0.2 %).

Identification of European diplozoids (Monogenea, Diplozoinae) by restriction digestion of the ribosomal RNA internal transcribed spacer.

The second internal transcribed spacer (ITS2) of the ribosomal RNA genes of Diplozoon paradoxum and Paradiplozoon nagibinae were amplified and sequenced. The polymerase chain reaction product of D. paradoxum was bigger (840 bp) than that of P. nagibinae (820 bp). There was no intraspecific variability recorded in sequences from either species. Sequence comparisons and ITS2 restriction fragment length polymorphism (RFLP) pattern of 8 European diplozoid species aimed to resolve their identification and amend the previous studies. RFLP was used to distinguish the 2 species from each other and from P. bliccae, P. homoion, P. megan, P. pavlovskii, P. sapae, and Eudiplozoon nipponicum, using restriction enzymes AluI, HaeIII, HinfI, RsaI, and SphI. The criteria for morphological identification of 8 European diplozoids are also included, with the main morphological characters of clamps, trapeze spur, and anterior joining sclerites of 8 diplozoid species being illustrated. Combination of the shape and comparison of length of the trapeze spur and anterior joining sclerites could lead to accurate identification of diplozoid species.

Abnormalities of the attachment clamps of representatives of the family Diplozoidae.

A comparative study has been made of the haptoral morphology of four species of diplozoon (Monogenea: Diplozoidae) from the gills of fish exposed to different levels of water pollution in two river systems in eastern Europe. An examination of the haptors of Paradiplozoon homoion (Bychowsky & Nagibina 1959), Paradiplozoon ergensi (Pejcoch 1968) and Paradiplozoon megan (Bychowsky & Nagibina 1959) from chub caught in the River Morava, Czech Republic and of Diplozoon paradoxum (Nordmann 1832) from bream recovered from the River Volga, Russia has revealed abnormalities to the attachment clamps. Two abnormal conditions were found: structural alterations to the attachment clamps and changes in the number of attachment clamps; these occurred both singly and in combination. A higher frequency of abnormal attachment clamps was found in diplozoons from fish caught in the more polluted localities of both rivers. The abnormalities have been recorded and their morphology compared in the light of conditions of environmental stress.

Treatment of fish parasites. 4. Effects of sym. triazinone (toltrazuril) on Monogenea.

For chemotherapy in fish parasitized by monogeneans, toltrazuril was tested in vivo and in vitro against gill-parasitizing species (Dactylogyrus vastator, D. extensus, D. cornu, Pseudodactylogyrus anguillae, Diplozoon paradoxum, Dip. homoion) as well as the skin-parasitizing species Gyrodactylus arcuatus. Naturally infected fish were incubated at 20 degrees C for 0.3, 1, 2, 3, 4, and 6h in water containing 0.5, 10, 20, 30, and 50 microgram toltrazuril/ml. In general, the damage observed resulted in the vacuolization and lysis of the parasitic tegument. Toltrazuril caused irreversible lesions in the tegument of Dactylogyrus species and Pseudodactylogyrus bini, beginning at a dose of 5 microgram/ml (4-h exposure). In vitro treatment with 10 microgram/ml toltrazuril caused death in Dip. paradoxum and Dip. homoion after 4-80 min, depending on the age of the parasites. Subadult worms were more susceptible to the drug than adults. Specimens of G. arcuatus were severely affected after 1-h exposure to 20 microgram/ml. In all species, the prohaptor and peduncle regions of the specimens were most sensitive to the drug. Treatment of infections of Gyrodactylus species, D. vastator, D. extensus, C. cornu, and P. bini using a water bath with 10 micrograms toltrazuril/ml for 4 h (D. cornu, 15 degrees C; other species, 20 degrees C) is recommended, since then species diagnosis is not needed. Fish with extensive skin lesions caused by net catching or infection by Saprolegnia spp. should be carefully observed during treatment, as these factors decrease their drug tolerance.

Treatment of fish parasites. 2. Effects of praziquantel, niclosamide, levamisole-HCl, and metrifonate on monogenea (Gyrodactylus aculeati, Diplozoon paradoxum).

In research for successful treatment of fish parasitized by monogeneans, four substances (Praziquantel, Niclosamide, Levamisole-HCl, and Metrifonate) were tested in vivo against Gyrodactylus aculeati parasitizing the skin of sticklebacks (Gasterosteus aculeatus). Fish were incubated in water containing different solutions of the drugs. Praziquantel, Niclosamide and Levamisole-HCl were effective against Gyrodactylus aculeati. Praziquantel caused irreversible lesions in the parasite tegument (beginning with 1 microgram/ml and 90 min exposure). Niclosamide was effective in a narrow concentration range of 0.075-0.1 microgram/ml (90 min). Levamisole-HCl was effective in a concentration range of 20-50 micrograms/ml for 120 min. Like Praziquantel, Niclosamide and Levamisole-HCl led to damage of the parasite tegument. The opisthaptor region and the openings of the cephalic glands were most severely affected. Furthermore, the effects of Niclosamide, Levamisole-HCl and Metrifonate on Diplozoon paradoxum parasitizing the gills of chubs (Squalius cephalus) and breams (Abramis brama) were investigated. Levamisole-HCl (10 micrograms/ml) and Niclosamide (0.2 microgram/ml) were effective against Diplozoon paradoxum after an exposure of 90 min and 45 min in vitro. The parasites were severely affected along the midbody. Metrifonate caused a lysis of the tegument and a strong secretion of slime. It is suggested that chemotherapy against Gyrodactylus sp. may be accomplished with 10 mg Praziquantel/l for 3 h during storage in smaller tanks. Niclosamide (0.1 mg/l for 90 min), or Levamisole-HCl (50 mg/l for 120 min) may be used alternatively. Concentrations of Niclosamide and Levamisole-HCl have to be calculated with accuracy, since fish only tolerate a very narrow range of these drugs (Niclosamide: 0.1 mg/l for 120 min; Levamisole-HCl: 50 mg/l for 120 min).

Treatment of fish parasites. 1. Praziquantel effective against Monogenea (Dactylogyrus vastator, Dactylogyrus extensus, Diplozoon paradoxum).

Treatment of fish parasites. 1. Praziquantel effective against Monogenea (Dactylogyrus vastator, Dactylogyrus extensus, Diplozoon paradoxum).

Seasonal Dynamics of Parasitoses in Grasscarp (Ctenopharyngodon idella) Fry and Fingerlings

WillomitzerJ J.: Seasonal Dynamics of Parasitoses in Grasscarp (Utenopharyn­ godon idella) Fry and Fingerlings. Acta vet. Brno, 49, 1980: 269 - 277. Examination of grasscarp (Ctenopharyngodon idella) fry and fingerlings from the State Fishery, Pohorelice, for 3 years revealed grasscarp infestation with 12 parasi­ te genera or species. The intensity and extensity of infestation was highest in the period August to October. The parasites involved were Chilodonella cyprini, Tri­ chodinella sp. and Trichodina domerguei f. magna, which were found from 1 week after hatching, and Diplostomum sp., Ichthyophthirius multifiliis, Dactylogyrus sp., Diplozoon paradoxum, Cryptobia branchialis, Eimeria sp., Piscicola geometra and Nematoda sp., which were demonstrated in grasscarp fingerlings. Moreover, there were a few findings of Cysticercus Gryporhynchus cheilancristrotus which confirmed a previous observation. Age-dependence of the intensity and extensity of infestation was apparent particularly in Diplostomum metacercariae where the rate of infection was' 100 % from 9 weeks of age and the number of parasites per host rose with advancing age from 1.4 at 3 weeks to 34.7 at 16 weeks. The intensity and extensity of Diplostomum metacercariae infection in grasscarp was related to the intensity and extensity of infestation with Diplostomum cercariae in intermediate host snails. Intensity and extensity of infestation, Cryptobia branchialis, Eimeria sp., Chilodonella cyprini, Lchthyophthirius multifiliis, Trichodina domerguei f. magna, Trichodinella sp., Dactylogyrus sp., Diplozoon paradoxum, Cysticercus Gryporhynchus cheilancristrotus Diplostomum sp., Nematoda sp., Piscicola geometra. A considerable rise in the production of herbivorous fish will probably be one of the tasks facing state fisheries in the next five-year-plans in Czechoslovakia. A prerequisite for this is the intro­ duction of artificial spawning. The role which herbivorous fish play in the production of animal

Fine structural observations on oocyte development in monogeneans

The ultrastructural changes accompanying oocyte differentiation in the ovaries of the monogeneans, Diclidophora merlangi, Diplozoon paradoxum and Calicotyle kröyeri have been described. In each case, oogenesis in the ovary proceeds as far as meiotic prophase in the primary oocyte. A three-stage sequence of development based on oocyte morphology is proposed: (1) Oogonia and early, immature primary oocytes are typically undifferentiated, with chromatin-laden nuclei occupying most of the cell volume. The cytoplasm contains small clumps of mitochondria and unattached ribosomal aggregates. There is evidence of mitosis and, in later stages, meiotic prophase is indicated by the appearance of nuclear synaptonemal complexes. (2) Maturing primary oocytes are characterized by increased nucleolar volume associated with the production of RNA for export to the cytoplasm. An organized GER and Golgi apparatus are established and involved in the synthesis and packaging of membrane-limited cortical granules. Annulate lamellae and nucleolus-like bodies appear in the cytoplasm and, with development, the cells increase in size and, peripherally, become interdigitated. (3) Mature primary oocytes represent a resting phase when cellular activity is minimal. Golgi disappear and the ER fragments or becomes reduced in dimensions. Mitochondria and free ribosomes are numerous and cortical granules move to the cell periphery. The cells separate and, when mature, are released from the ovary. There are minor species differences in oocyte ultrastructure and development.

Ultrastructural observations on mehlis' gland in the monogeneans, Diplozoon paradoxum and Calicotyle kröyeri

Mehlis' gland of both Diplozoon paradoxum and Calicotyle kröyeri is composed of two cell types that taper to form ducts opening into the lumen of the ootype. The cells are invested with fibrous interstitial material and form a close structural relationship with surrounding parenchyma. The most prevalent cell type, the S 1 cell, is characterized by an extensive GER with narrow cisternae containing a finely granular material, and numerous Golgi stacks involved in the formation of multi-vesicular secretory bodies. In the S 2 cells the GER cisternae are greatly distended with a finely filamentous material and the Golgi give rise to dense secretory bodies with a packed fibrous appearance. There are species differences in the fine structure of the secretory bodies and these may reflect differences in the chemical composition of the glands. The ducts of the glands are lined with microtubules and are anchored to the ootype epithelium by septate desmosomes. They convey the secretory products to the ootype where they are released, apparently by exocytosis involving membrane fusion, into the lumen. The ootype is lined by a highly folded cellular epithelium which in D. paradoxum is ciliated. The cells contain profiles of GER and Golgi complexes and produce a third type of secretion which is also discharged into the ootype lumen.

Vitelline cell development in monogenean parasites.

Histochemical and electron microscopic studies of the vitellaria of three polyopisthocotylean fish-gill flukes,Diplozoon paradoxum, Diclidophora merlangi andD. denticulata, and one monopisthocotylean fish-skin fluke,Calicotyle kroyeri have shown that, in each case, vitelline cell development is basically similar. Immature vitelline cells are typically embryonic and undifferentiated. InD. paradoxum they display annulate lamellae, and inC. kroyeri they are invested with flat, sheet-like extensions of the parenchyma. Differentiation into maturing vitelline cells involves the development of extensive GER, Golgi complexes and the production of dense droplets of shell-protein. With the onset of maturity, protein synthesis stops and, as the GER disintegrates, the cell develops food-reserves in the form of yolk bodies, glycogen and lipid. It is then released into the vitelline ductlet. These processes occur in all the follicles at the same time, and all stages of development can be found in any one follicle.