The genetic relatedness of two kidney-parasitic Sphaerospora species was studied. Although S. renicola, the causative agent of swimbladder inflammation of common carp fingerlings (Cyprinus carpio), and Sphaerospora sp. originating from goldfish (Carassius auratus auratus) were indistinguishable on the basis of spore morphology, they were found to be genetically different as their 18S rDNA sequences shared only 71.9% identical nucleotides. In the phylogenetic trees, Sphaerospora sp. from goldfish grouped with Myxidium truttae (AJ582061) within the clade of the coelozoic freshwater species. Sphaerospora renicola clustered with S. molnari (AF378345) within the group of myxosporeans histozoic in gills. The topology of the six Sphaerospora species on the phylogenetic trees implied that myxospore morphology does not correlate with the genetic relationships, and the genus seems to be polyphyletic.
Sinergasilus lieni Yin, 1949, a well-known and pathogenic parasitic copepod in China and Russia, has been detected in Hungarian carp farms for the first time. The parasite infected the third-year generation of silver carp (Hypophthalmichthys molitrix) and bighead (Aristichthys nobilis). The gills of the infected fish specimens showed severe pathological changes. At the attachment sites of female copepods clubbing and fusing of the gill filaments were observed and in some parts of the pale or whitish hemibranchia deep indentations were recorded in places where the tips of the damaged filaments had broken off. Silver carp and bighead were infected at a similar rate, having 8 to 27 copepods attached to the end of the clubbed filaments or the proliferated epithelium of 2 to 10 fused filaments. In histological sections the head part of the parasite was found in a deep cavity of the proliferated epithelium, piercing its antennae deep into the tissues. Only the end of the filaments showed changes. In this part the proliferated epithelium was infiltrated by eosinophilic granular cells. In the central and basal parts of the hemibranchia the original structure of the filaments was preserved with intact secondary lamellae.
During a five-year survey including studies on the parasite fauna of bream (Abramis brama), four gill-parasitic Myxobolus species (M. bramae, M. hungaricus, M. impressus and M. macrocapsularis) were recorded in a total of 313 breams from Lake Balaton. The commonest species, M. bramae showed a prevalence of 33%, while the other species occurred sporadically. Myxobolus bramae and M. macrocapsularis infected the tips of the gill filaments and caused both intralamellar and interlamellar infection. Intralamellar plasmodia of small size developed in the capillary network of the gill lamellae whereas the much larger interlamellar plasmodia were formed in the arteria afferens. The intralamellar plasmodia of M. hungaricus always infected the basal or central part of the gill filaments. In contrast to the above species developing in the blood vessels, M. impressus proved to be an epithelial parasite, as its plasmodia always developed in the adjacent gill filaments of two opposite haemibranchia, in the stratified epithelium between the respiratory plates, causing changes of the haemibranchium which were well visible even by the naked eye.
The actinospore consumption of copepods (Cyclopsspp.)was demonstrated by laboratory observations. It was observed that in experimental dishes the number of actinospores floating in the water decreased, or such actinospores were completely eliminated, in the presence of copepods. The ingestion of actinospores by copepods and their further fate were monitored by fluorescent staining and by conventional histological techniques. The actinospores were observed to have got caught on the filters of Cyclopsspp. Two and a half hours after the copepods had been placed into water containing actinospores, their digestive tract was found to contain spores that had extruded their filaments from the polar capsules. After copepods having ingested the actinospores of the species Myxobolus pseudodisparhad been fed to roaches, no muscle infection developed in the fish host. It is likely that Cyclopsspp. can filter out actinospores floating in the water also from natural waters, thus decreasing the chance of development of myxosporean infections.
Oligochaetes living in the Mijares River close to the Sitjar reservoir, and polychaetes from the brackish and marine waters of a channel flowing into the Mediterranean Sea, both in the province of Castellón (Spain), were examined for the presence of actinosporea. An aurantiactinomyxon was isolated from 60 specimens of the oligochaete Branchiura sowerbyi collected from the river, but no actinospores were isolated from 160 polychaetes collected from the sea channel. The aurantiactinospores were detected by the cell-well plate method. The detected species are not identical with any of the aurantiactinomyxon forms hitherto described in the literature. This is the first report on the occurrence of an actinosporea in Spanish waters.
During a survey on
infection of pond-cultured common carp in Syria three
spp. were found.
infected the gill arteries, forming large elongated plasmodia in the gill filaments. The plasmodia of
were located in the gill arches at the base of the filaments. Elongated filiform plasmodia of
were found in the blood vessels of the brain. Despite the common occurrence of the above parasites, no disease symptoms were observed in the infected fish specimens. This is the first report on myxosporean infection of fish from Syrian waters.
The weight of internal organs (swimbladder, kidney, liver, spleen) in relation to the body weight was studied in common carp fingerlings divided into three groups on the basis of swimbladder appearance and microscopic examination of the kidney. The fish had been collected from different Hungarian fish farms at the time when swimbladder inflammation (SBI) usually occurs (in July and August). The first group comprised fish with severe signs of SBI and massive renal sphaerosporosis, the second group consisted of fish with milder swimbladder changes and/or kidney infection by a low number of Sphaerospora renicola, while the third group was constituted by infection-free common carp fry. Statistical analysis of swimbladder, kidney, liver and spleen weight in relation to the body weight revealed that in the infected groups the internal organs were substantially enlarged. This suggests that in common carp fry with SBI the swimbladder changes are accompanied by reno-, hepato- and splenomegaly.
European eel is a catadromous fish species, which means that after living in freshwater premature individuals adapt to sea water, and migrate to the Sargasso Sea for spawning. Although male eel can be sexually matured even in freshwater, to date, it was believed that female eel can be matured only in seawater. Here we show that the process of sexual maturation may be induced in freshwater by treating female eels with carp pituitary (GSI = 9.87±1.55%). It is thus proposed that seawater condition is not an obligatory environment for stimulating gametogenesis and for artificial maturation of the European eel in neither gender.
Radiodiagnostic methods have not been used previously for studying the anatomy and diseases of the swimbladder of freshwater fish species. In this study, the radiographic anatomy of the swimbladder and species-related differences in swimbladder structure were studied on plain radiographs taken of 12 Hungarian fish species of major economic importance. Changes observed by radiography were also studied by conventional parasitological methods. The radiodiagnostic method reported here appears to be a useful complement to diagnostic examinations that have been based merely on dissection so far. It enables evaluation of the pathological lesions in live condition, without causing damage to the fish.