Argentophilic structures as a diagnostic criterion for the discrimination of species of the genus Gyrodactylus von Nordmann (Monogenea)

The mapping of argentophilic surface sensory structures (chaetotaxy) is a technique which has contributed to the taxonomy of larval digeneans. Four species of Gyrodactylus from four different hosts (Salmo salar, Gasterosteus aculeatus, Poecilia reticulata and Carassius auratus) were investigated using this technique in order to ascertain its usefulness in distinguishing species of this monogenean genus. A formula for the arrangement of the natural aggregations of sensilla similar to those prepared for cercariae is proposed. Although the greatest concentration of sensilla occur adjacent to the anterior extremity of the body, it is the region just posterior to the pharynx which most readily permits the discrimination of Gyrodactylus spp. based on the number and spatial configuration of these sensilla. Maps have been constructed to demonstrate these differences. It is concluded that chaetotaxy shows potential as a simple and reliable method of distinguishing species of this genus.     

First description of monogenean parasites in Lake Tanganyika: the cichlid Simochromis diagramma (Teleostei, Cichlidae) harbours a high diversity of Gyrodactylus species (Platyhelminthes, Monogenea)

Lake Tanganyika harbours the most diverse endemic cichlid fish assemblage of Africa, but its monogenean fish parasites have not been investigated. Here we report, for the first time, on the Gyrodactylus parasites in this hotspot of fish biodiversity. Haptor morphometrics and nuclear ribosomal DNA sequences revealed 3 new species on Zambian Simochromis diagramma: Gyrodactylus sturmbaueri n. sp., G. thysi n. sp. and G. zimbae n. sp. Their distinct morphology and strong genetic differentiation suggest that they belong to distant lineages within the genus Gyrodactylus, and phylogenetic reconstructions suggest affinities with other genera of gyrodactylids. Additional U-shaped haptoral plates in G. thysi n. sp. and a second large spine-like structure in the male copulatory organ of G. zimbae seem to represent new features for the genus. Such large diversity on a single host species can probably be explained by host-switching events during the course of evolution, in agreement with the generally accepted concept that ecological transfer is an important aspect of gyrodactylid speciation. Additional parasitological surveys on other host species, covering a broader phylogenetic and geographical range, should clarify the evolutionary history of Gyrodactylidae on cichlids in the African Great Lake and other parts of Africa.     

Chaetotaxy of members of the Gyrodactylidae (Monogenea), with comments upon their systematic relationships with the Monopisthocotylea and Polyopisthocotylea

This study investigates intra- and inter-generic variation in the chaetotaxy pattern of members of the Gyrodactylidae and compares these data with those from other monogenean groups elucidated by other workers. The staining of surface sensillary structures has revealed areas of homology between the two genera Gyrodactylus and Ooegyrodactylus, which have markedly contrasting modes of reproduction. Although species specific maps have been elucidated for members of the genus Gyrodactylus, no evolutionary trends in their sensillary patterns could be determined. Members of the family Gyrodactylidae are shown to possess a cluster of 3 × 2 sensilla, similar in their size and arrangement to the post-ocular (spo) cluster of sensilla in polyopisthocotyleans, although on the opposite surface. A comparable cluster of sensilla is lacking in monopisthocotyleans. This information gathered from chaetotaxy supports the proposal that the order Gyrodactylidea is close to the polyopisthocotylean line of monogenean evolution.     

The mitochondrial genome of Gyrodactylus derjavinoides (Platyhelminthes: Monogenea)--a mitogenomic approach for Gyrodactylus species and strain identification

Systematists and evolutionary biologists are constantly on the lookout for new sources of characters to discriminate amongst taxa and estimate interrelationships within and between taxa. Entire mitochondrial genomes provide a wealth of data, both at the nucleotide and amino acid level. Molecular markers are of particular utility when applied to small, morphologically conserved taxa, as is the case for many monogenean ectoparasites of fish. Gyrodactylus species display a considerable degree of anatomical conservatism, complicating diagnostics based solely on morphology, and some are significant pests of wild and cultured fish. Here we sequenced the complete mitochondrial genome of Gyrodactylus derjavinoides Malmberg, Collins, Cunningham & Behiar 2007, one of the most frequently found gyrodactylid species on salmonids in Scandinavia, and compared it with the recently published genomes of Gyrodactylus salaris Malmberg, 1957 and Gyrodactylus thymalli Zitnan 1960. Through comparative sliding window analysis we identified regions of high sequence variability and designed new primer sequences. In total, 6 new primer pairs have been developed, amplifying fragments of cox1, cox3, nad1, nad2, nad4, nad5 and atp6. Together, they amplify regions capturing almost half the nucleotide variability present in the complete mitochondrial genome. These degenerate primers should also work for other Gyrodactylus species parasitizing salmonids. In addition, we developed a multiplex assay that simultaneously amplifies four fragments in a single PCR reaction. Besides the diagnostic value, these fragments can be used for studying the transmission dynamics of Gyrodactylus, providing crucial information for an improved understanding of the spread and epidemiology of these important fish pathogens.     

Experimental infections of the monogenean Gyrodactylus turnbulli indicate that it is not a strict specialist

Parasites represent a threat to endangered fish species, particularly when the parasite can host switch and the new host is vulnerable. If the parasite is highly host specific then successful host switching should be a rare occurrence; however, the host range of many parasites which are assumed to be specialists has never been tested. This includes the monogenean Gyrodactylus turnbulli, a well-studied ectoparasite found caudally on its known host, the guppy, Poecilia reticulata. In this study, we monitored parasite establishment and reproduction on a range of poeciliids and more distantly related fish. Individually maintained fish were experimentally infected with a single parasite and monitored daily to establish whether G. turnbulli could survive and reproduce on other fish species. Gyrodactylus turnbulli can infect a wider range of hosts than previously considered, highlighting the fact that host specificity can never be assumed unless experimentally tested. Our findings also have significant implications for parasite transmission to novel hosts and provide further insight into the evolutionary origins of this ubiquitous group of fish pathogens. Previous molecular evidence indicates that host switching is the key mechanism for speciation within the genus Gyrodactylus. Until recently, most Gyrodactylus spp. were assumed to be narrowly host specific. However, our findings suggest that even so-called specialist species, such as G. turnbulli, may represent a threat to vulnerable fish stocks. In view of the potential importance of host switching under artificial conditions, we propose to describe this as 'artificial ecological transfer' as opposed to 'natural ecological transfer', host switching under natural conditions.     

Gyrodactylus longidactylus n. sp., a monogenean from Pomatoschistus lozanoi (de Buen) (Gobiidae) from the North Sea

Gyrodactylus longidactylus n. sp., a gyrodactylid monogenean parasitising the gills of Pomatoschistus lozanoi (de Buen, 1923) in the North Sea is described. It is a species with rather small anchors which are only connected to a ventral bar which lacks a ventral bar membrane. The marginal hooks have long handles, which are always longer than the total length of the anchor. The pharynx has long pharyngeal processes. Measurements, drawings of the opisthaptoral hard parts, penis and pharynx, and SEM micrographs of this monogenean are presented. G. longidactylus n. sp. is the first monogenean species described from P. lozanoi.     

The nuclear rDNA region of Gyrodactylus arcuatus and G. branchicus (Monogenea: Gyrodactylidae)

The primary structure of the ribosomal DNA internal transcribed spacers (ITS-1 and ITS-2) and 5.8S rRNA gene were used to characterize and identify 2 monogenean species of Gyrodacrylus living externally on the threespine stickleback (Gasterosteus aculeatus). The ITS region was amplified by PCR from freshwater, brackish, and marine isolates of Gyrodactylus arcuatus and G. branchicus, and the ends of the coding regions were identified by comparative alignment. No intraspecific and very low interspecific variation were observed in the 5.8S rRNA gene; high inter- and low intraspecific variation were revealed in the ITS-1 and ITS-2 regions. The morphological species identification was in all cases confirmed by the molecular identification. Intraspecifically, samples from 2 locations in the North Sea could be differentiated, but the Baltic sample resembled North Sea genotypes. Our approach offers perspectives for a multimetric genetical, morphometrical, and ecological taxonomy of the genus Gyrodactylus.     

Shrimps remove ectoparasites from fishes in temperate waters

We have found that two very common species of North Atlantic shallow water shrimp, Palaemon adspersus and Palaemon elegans, remove and feed on ectoparasites on plaice (Pleuronectes platessa L.). The relationship could be mutualistic, as we did not observe any attempts by the fishes to feed on the shrimps. The ectoparasites removed included monogenean worms (Gyrodactylus sp.) and sea lice (Lepeophtheirus pectoralis). An experiment showed that there were 65% more Gyrodactylus parasites on the fishes that had been apart from compared with those that had been together with shrimps for 48h. Shrimps on coral reefs are known for cleaning fishes, but that shrimps in temperate waters show parasite-cleaning behaviour is, to our knowledge, a new observation.     

A new monogenean species,Gyrodactylus ajime n. sp. (Gyrodactylidae), parasitic on Niwaella delicata (Niwa), an endemic loach of Japan

A new gyrodactylid species, Gyrodactylus ajime n. sp., is described from the skin and fins of an endemic and commercially important loach Niwaella delicata (Niwa) (Cypriniformes: Cobitoidea: Cobitidae), from the upper reach of the River Yura in Ashiu, Kyoto Prefecture, Japan with scanning electron microscopy observations and molecular data. This species can be distinguished from congenerics by characteristics of the sickle of the marginal hook: the sickle proper is composed of two straight sections and a curved section; its short point extends beyond the limit of the toe and is directed downwards; and the upper corner of heel angular is slightly raised. There are 31 species and subspecies of native loaches (Cobitoidea) known from Japan, of which 25 are red-listed nationally, and two are commercially important. I reviewed all reports of monogeneans from Japanese loaches, and found that only five fish species have been recorded as hosts of these parasites. This suggests that the parasite fauna of these fishes is poorly described. It is urgent to thoroughly describe the monogenean parasites of loaches in Japan as some of the parasite species may be threatened with co-extinction because their hosts are threatened, and to understand any negative impacts on commercially important fish species.

     

鱼类三代虫研究进展

三代虫是一类常见的鱼类体表寄生虫,广泛寄生于各种鱼类,其危害近年有加剧之势,对鱼类养殖业造成较大威胁。本文从三代虫的分类方法、种群动态和引起寄主免疫反应等方面综述了鱼类三代虫研究现状及发展趋势。     

Monogenean parasites from Clariidae (Teleostei, Siluriformes) in Cameroon: I. Description of two new species of Gyrodactylus from the Nyong basin

The study of gill and skin parasites of three fishes species belonging to the genus Clarias: C. camerunensis, C. jaensis and C. pachynema, from the Nyong basin (Cameroon), revealed the presence of two new Monogenean species of the genus Gyrodactylus Nordmann: G. camerunensis n. sp. and G. nyongensis n. sp. parasite of Clarias camerunensis, C. jaensis and C. pachynema. Gyrodactylus camerunensis n. sp. is clearly distinguished from G. nyongensis n. sp. by the smaller size of the haptor sclerites. These two new species differ also from their closest African relatives of the genus Gyrodactylus, G. rysavyi, G. clarii and G. alberti, by the morphology and size of the haptorail sclerites. Their host specificity was discussed and appeared stenoxenous (mesostenoxenous).     

Infections of Gyrodactylus bullatarudis and Gyrodactylus turnbulli on guppies (Poecilia reticulata) in Trinidad.

Gyrodactylus bullatarudis Turnbull, 1956, and Gyrodactylus turnbulli Harris, 1986, are recorded from guppies (Poecilia reticulata) from the northern mountains of Trinidad. Mixed infections of the 2 species were found at 9 localities. Gyrodactylus turnbulli had a predominantly posterior distribution on the fishes, whereas G. bullatarudis was more anteriorly distributed. This is the first record of these species from guppies collected from within their original range.     

Chigger mites of the genus Leptotrombidium: key to species and their distribution in China

Chigger mites of the genus Leptotrombidium (Acari: Trombiculidae) transmit scrub typhus, caused by Rickettsia tsutsugamushi (= R.orientalis) in South-East Asia. In China, eighty-two species of Leptotrombidium have been recorded; these are listed with the names of Provinces where they were found. Five species, L.deliense, L.insularae, L.kaohuense, L.rubellum and L.scutellare, have been implicated as Chinese vectors of scrub typhus. A brief key is given to the larvae of all but three of the Leptotrombidium mites known in China.     

Determinants of parasite species richness on small taxonomical and geographical scales: Lamellodiscus monogeneans of northwestern Mediterranean sparid fish

Determinants of parasite species richness have been investigated in a host-parasite system comprising fish of the family Sparidae and their monogenean gill ectoparasites of the genus Lamellodiscus. This study was carried out on a small geographical scale in the northwestern Mediterranean Sea. Host phylogenetic relationships were taken into account by phylogenetic eigenvector regression which required the reconstruction of a phylogenetic tree for the sparid fish species using mtDNA sequences. Several ecological variables potentially acting on Lamellodiscus species richness were considered. Host body size and host migratory behaviour appeared to be the main determinants of parasite species richness in this system. It is concluded that structuring of monogenean communities is controlled more by ecological than evolutionary factors.     

鱼类三代虫的寄主特异性分析

分析了迄今为止世界范围三代虫的寄主情况。三代虫具有很强的寄主特异性,并且在种、属及科等水平上的特异性均有较明显差异;分析同一种寄主上所寄生的三代虫种类之间的关系,显示大部分寄主只寄生一种三代虫,体现出了三代虫很强的寄主特异性。     

Parasite fauna of young landlocked salmon (Salmo salar m. Sebago girard) in the Pista River (the White Sea Basin)

A native population of landlocked salmon of the Pista River was investigated in 2000-2002. Adult salmon in Pista River has smallest size among other populations of landlocked salmon in Karelia. Data on the biology and parasite fauna of young salmon are presented. The presence of local salmon populations in lakes of the river system is apparently one of the mechanisms keeping the magnitude of population. The presence of Gyrodactylus salaris, a harmful parasite of the young landlocked salmon, is established in this territory for the first time. This monogenean species is believed to have been introduced into the Pista River via stocking from Finland.     

Chronological analysis of the species of Conus described during the 18th century

The 339 species-group names in the gastropod genus Conus proposed between 1758 and 1800 have been analyzed in chronological order, in order to (1) identify each nominal species, and (2) determine the correct name of each valid species. Additions and corrections are given to the author's series of papers on type specimens and identity of the described species of Conus. A table listing the 339 species-group names alphabetically indicates the present locations of the 124 known type specimens and the status of each name. At present, 123 valid species are recognized (118 Recent, 5 Tertiary), 159 names are synonyms of previously or simultaneously described species, 35 are nomina dubia, 19 are assigned to infrasubspecific rank, and 3 have been trandferred to genera in other families. Problems involving homonymy of 44 names have been resolved. The proportion of valid species to described species remained quite constant (about 80%) between 1758 and 1786, but then declined sharply to 40%. By 1800, although only 13% of all known species-group names in Conus had been introduced, they probably account for 25% of the known valid Recent species. Extension of the chronological study to species described through 1840 may establish the correct names of half the valid Recent species of Conus.