Genetic variation of fish parasite populations in historically connected habitats: undetected habitat fragmentation effect on populations of the nematode Procamallanus fulvidraconis in the catfish Pelteobagrus fulvidraco

Habitat fragmentation may have some significant effects on population genetic structure because geographic distance and physical barriers may impede gene flow between populations. In this study, we investigated whether recent habitat fragmentation affected genetic structure and diversity of populations of the nematode Procamallanus fulvidraconis in the yellowhead catfish, Pelteobagrus fin't4draco. The nematode was collected from 12 localities in 7 floodplain lakes of the Yangtze River. Using I I intersirnple sequence repeat markers, analysis of molecular variance showed that genetic diversity occurred mainly within populations (70.26%). Expected heterozygosity (He) of P. fulvidraconis was barely different between connected (0.2105) and unconnected lakes (0.2083). Population subdivision (Fst) between connected lakes (0.2177) was higher than in unconnected lakes (0. 1676). However, the connected and unconnected lakes did not Cluster into 2 clades. A Mantel test revealed significant positive correlation between genetic and geographic distances (R = 0.5335, P < 0.01). These results suggest that habitat fragmentation did not cause genetic differentiation among populations or a reduction of diversity in isolated populations of P. fulvidraconis. At least 2 factors may increase the dispersal range of the nematode, i.e., flash flooding in summer and other species of fish that may serve as the definitive hosts. Moreover, lake fragmentation is probably a recent process; population size of the nematode in these lakes is large enough to maintain Population structure.

Description of two new myxosporean species parasitic in freshwater fishes from the Yangtze River in China

Two new species of myxosporeans (Myxosporea: Myxidiidae), Myxidium tuanfengensis sp. n. and Zschokkella saurogobionis sp. n., Parasitic in freshwater fishes collected from the Yangtze River of China are described in this paper. M. tuanfengensis was found in the liver parenchyma and intestine lumen of Leptobotia taeniops Sauvage, 1878, while Z. saurogobionis was found in the gall bladder of Saurogobio dumerili Bleeker, 1871. The diagnostic characters of M. tuanfengensis are: round or elliptical polysporous plasmodia averaging 118 mum in size; spore oval in frontal view with smooth surface and nearly spindle-shape in sutural view with slightly sinuous sutural ridge, averaging 19.5 x 9.75 x 8.9 mum in size; two large spherical polar capsules 6.8 mum in diameter, with polar filament wound in 4 to 5 coils. The diagnostic characters of Z. saurogobionis are: spore elliptical in both frontal and sutural view measuring 18.3 x 9.8 x 10.8 mum in size; fine sutural ridge in S-form, spore shell marked with 10 to 12 distinct lines paralleled with the sutural line; two spherical polar capsules, 6.7 mum in diameter, with polar filament in 5 coils.

First description of the male and redescription of the female of Philometra clavaeceps Dogiel and Akhmerov, 1959 (Nematoda : Philometridae), a parasite of east Asian cyprinid fish

The first description of the male and a redescription of the female of the nematode Philometra clavaeceps Dogiel and Akhmerov, 1959, a parasite of east Asian cyprinids, are presented on the basis of specimens collected from Culter erythropterus Basilewsky and Culler dabryi Bleeker from Liangzi Lake (the Yangtze River basin), Hubei Province, central China. Gravid females from the fish abdominal cavity, penetrating often into ovaries, occurred in May-June, whereas conspecific males and young mature females on the swimbladder were recorded in January. Philometra clavaeceps seems to have a pronounced annual maturation cycle in the locality. The finding of P. clavaeceps in C. dabryi represents a new host record.

Communities of gastrointestinal helminths of fish in historically connected habitats: habitat fragmentation effect in a carnivorous catfish Pelteobagrus fulvidraco from seven lakes in flood plain of the Yangtze River, China

Background: Habitat fragmentation may result in the reduction of diversity of parasite communities by affecting population size and dispersal pattern of species. In the flood plain of the Yangtze River in China, many lakes, which were once connected with the river, have become isolated since the 1950s from the river by the construction of dams and sluices, with many larger lakes subdivided into smaller ones by road embankments. These artificial barriers have inevitably obstructed the migration of fish between the river and lakes and also among lakes. In this study, the gastrointestinal helminth communities were investigated in a carnivorous fish, the yellowhead catfish Pelteobagrus fulvidraco, from two connected and five isolated lakes in the flood plain in order to detect the effect of lake fragmentation on the parasite communities. Results: A total of 11 species of helminths were recorded in the stomach and intestine of P. fulvidraco from seven lakes, including two lakes connected with the Yangtze River, i.e. Poyang and Dongting lakes, and five isolated lakes, i.e. Honghu, Liangzi, Tangxun, Niushan and Baoan lakes. Mean helminth individuals and diversity of helminth communities in Honghu and Dongting lakes was lower than in the other five lakes. The nematode Procamallanus fulvidraconis was the dominant species of communities in all the seven lakes. No significant difference in the Shannon-Wiener index was detected between connected lakes (0.48) and isolated lakes (0.50). The similarity of helminth communities between Niushan and Baoan lakes was the highest (0.6708), and the lowest was between Tangxun and Dongting lakes (0.1807). The similarity was low between Dongting and the other lakes, and the similarity decreased with the geographic distance among these lakes. The helminth community in one connected lake, Poyang Lake was clustered with isolated lakes, but the community in Dongting Lake was separated in the tree. Conclusion: The similarity in the helminth communities of this fish in the flood-plain lakes may be attributed to the historical connection of these habitats and to the completion of the life-cycles of this fish as well as the helminth species within the investigated habitats. The diversity and the digenean majority in the helminth communities can be related to the diet of this fish, and to the lacustrine and macrophytic characters of the habitats. The lake isolation from the river had little detectable effect on the helminth communities of the catfish in flood-plain lakes of the Yangtze River. The low similarities in helminth communities between the Dongting Lake and others may just be a reflection of its unique water environment and anthropogenic alterations or fragmentation in this lake.

Occurrence of Camallanus cotti in greatly diverse fish species from Danjiangkou Reservoir in central China

Two thousand four hundred fifty-eight fish comprised of 53 species were captured in the Danjiangkou Reservoir, in the northwestern part of Hubei Province, central China during 2004, to examine Camallanus cotti infections. We found that 19 cypriniform, 3 siluriforme, and 4 perciforme fishes were infected by the nematode. Our study revealed the species, Hemiculter bleekeri bleekeri, Culter oxycephaloide, Pseudolaubuca sinensis, Acanthobrama simony, Mylopharyngodon piceus, Ctenopharyngodon idella, Gnathopogon imberbis, G. argentatus, Saurogobio dabryi, S. dumerili, Gobiobotia ichangensis, Liobagrus marginatoides, and Ctenogobius shennongensis as new hosts of the worm. The number and range of fish host species found in this survey were much greater than any of the previous investigations. The mean prevalence, prevalence, mean abundance, and intensity of infection varied in different fish species, indicating a possible host preference. Moreover, we suggest that this nematode is a native parasite of cypriniform fishes in China, perhaps initially in the reaches of the Yangtze River.

Trophic relationship between the parasitic isopod ichthyoxenus japonensis and the fish carassius auratus auratus as revealed by stable isotopes

Stable carbon and nitrogen isotope analysis was used to investigate the host-parasite trophic relationship between the parasitic isopod Ichthyoxenus japonensis and one of its freshwater fish host Carassius auratus auratus from Lake Fuxian, China. No significant differences in delta C-13 and delta N-15 were observed between the heterosexual pairs of I. japonensis in the same host. delta C-13 and delta N-15 of I. japonensis were significantly lower than those of its host fish, and the isotopic ratios of the isopod increased with the increase of host fish isotopic signatures. Unlike isotopic fractionation patterns generally observed among consumers and their diets, isopod parasite was delta C-13 and N-15 depleted relative to the muscle tissue of this host fish. Differential isotopic fractionation patterns in the isopod parasite and the fish may be attributed to differences in parasite and host metabolism.

Redescription of Trypanosoma siniperca Chang 1964 from freshwater fish of China based on morphological and molecular data

During the parasite fauna investigation within 2005, the freshwater fish trypanosome Trypanosoma siniperca Chang 1964 was isolated from the blood of Mandarin carp (Siniperca chuatsi) from Niushan Lake, Hubei Province, central China. Blood trypomastigotes were observed only, and the density of infection was low. Light microscopy examinations of this material made it possible to study in detail the morphology of this parasite and redescribe it according to current standards. T. siniperca is characterized also on the molecular level using the sequences of SSU rRNA gene. Phylogenetic analyses based on these sequences allowed clearer phylogenetic relationships to be established with other fish trypanosomes sequenced to date.

The costs and benefits in an unusual symbiosis: experimental evidence that bitterling fish (Rhodeus sericeus) are parasites of unionid mussels in Europe

Interspecific symbiotic relationships involve a complex network of interactions, and understanding their outcome requires quantification of the costs and benefits to both partners. We experimentally investigated the costs and benefits in the relationship between European bitterling fish (Rhodeus sericeus) and freshwater mussels that are used by R. sericeus for oviposition. This relationship has hitherto been thought mutualistic, on the premise that R. sericeus use mussels as foster parents of their embryos while mussels use R. sericeus as hosts for their larvae. We demonstrate that R. sericeus is a parasite of European mussels, because it (i) avoids the cost of infection by mussel larvae and (ii) imposes a direct cost on mussels. Our experiments also indicate a potential coevolutionary arms race between bitterling fishes and their mussel hosts; the outcome of this relationship may differ between Asia, the centre of distribution of bitterling fishes, and Europe where they have recently invaded.

Scanning electron microscopy of Aspidogaster ijimai Kawamura, 1913 and A-conchicola Baer, 1827 (Aspidogastrea, Aspidogastridae) with reference to their fish definitive-host specificity

Two species of aspidogastreans, namely Aspidogaster ijimai and A. conchicola, were studied by scanning electron microscopy. In nine lakes and an old river course, the Tian'ezhou oxbow, investigated in the flood plain of the Yangtze River, A. ijimai was obtained from the common carp (Cyprinus carpio) in three lakes, and A. conchicola from the black carp Mylopharyngodon piceus in three lakes and the oxbow. In none of the localities, however, were the two species found together. It is suggested that A. ijimai may be considered as a specialist parasite for the common carp, at least in the flood-plain lakes of the Yangtze River. The two parasites were similar in many aspects of their morphology. Their bodies can both be separated into a dorsal part and a ventral disc, with the body surface of the dorsal part elevated by transverse folds, and the disc subdivided into alveoli by transverse and longitudinal septa, although the number of alveoli was different in the two species. The depression on the ventral surface of the neck region was prominent for both species, and their ventral disc was covered densely with non-ciliated bulbous papillae. The position of mouth, osmo-regulatory pore and marginal organ was also similar for A. ijimai and A. conchicola. However, microridges in the trough of the folds in the neck region and numerous small pits on the upper part of the septa were found exclusively in A. ijimai, but uniciliated sensory papillae in A. conchicola.

Occurrence of Bothriocephalus acheilognathi in cyprinid fish from three lakes in the flood plain of the Yangtze River, China

Cyprinid fish, Hemiculter leucisculus, Cultrichthys erythropterus and Culter dabryi, were sampled from Liangzi, Honghu and Tangxun lakes in the flood plain of the Yangtze River. The cestode Bothriocephalus acheilognathi Yamaguti, 1934 was found in the 3 lakes, but C. erythropterus sampled from Liangzi lake was found uninfected due probably to the small sample size. Findings of the cestode in the 3 lakes represent the first record of the parasite in the flood plain of the Yangtze River, indicating that B. acheilognathi may be distributed much wider in China than previously recognized.

Evidence of host blood feeding by the monogenean, Ancyrocephalus mogurndae (Monogenea : Ancyrocephalidae) from the gills of the mandarin fish, Siniperca chuatsi

By examining iron contents, it is demonstrated that the monogenean Ancyrocephalus mogurndae (Yamaguti, 1940) feeds on the blood of its host, the mandarin fish Siniperca chuatsi (Basilewsky). The iron content and then the quantity of blood necessary to produce this amount of iron are found different in young and fully-matured worms. Young worms contain higher levels of iron and estimated amount of blood. It is suggested that A. mogurndae may start to feed on host blood as attached on gills, and the amount of blood ingested by young worms may vary from 0.01 to 1.00 mu l before reproduction. The difference between young and fully-matured worms may be accounted for by the elimination of haematin and change of food composition in matured worms and may also be affected by reproduction. Experimental infections of the monogenean may provide supportive information for explaining the difference, and further studies should also examine the effect of immune components in host blood ol mucus on the intestines of the parasite.

Co-occurrence and microhabitat of Ancyrocephalus mogurndae (Monogenea) and Henneguya weishanensis (Myxosporea) on gills of the mandarin fish, Siniperca chuatsi

Seasonal variations in a population of the monogenean Ancyrocephalus mogurndae Gussev, 1955 were investigated on gills of cage-cultured mandarin fish, Siniperca chuatsi (Basilewsky), during the period from April 1994 to April 1995. The abundance of A. mogurndae peaked in late spring and summer. Prevalence was high (75-100 %) throughout the study period, and did not vary significantly between months. More than 50 % of all monogeneans were found on the first and second gill arches, except one occasion when the fourth gill arch had the majority in April 1995. The niche breadths were significantly correlated with the population abundance. A coexistent parasitic myxosporean, Henneguya weishanensis Hu, 1965, on the gills of the fish was found to have little influence on the gill-arch preference of the monogenean, although the monogenean abundance was higher in those fish infected with the myxosporean.

Effects of the “all-fish” GH (growth hormone) transgene expression on resistance to Ichthyophthirius multifiliis infections in common carp, Cyprinus carpio L.

A study was undertaken on the susceptibility of the F-4 generation of "all-fish" growth hormone transgenic carp, Cyprinus carpio L, against Ichthyophthirius multifiliis infections. When 1-year old, transgenic carp, with non-transgenic carp and non-manipulated carp (controls) were split into three batches, and experimental infections were performed throughout the 3-month period. All 72 fish were successfully infected. It was shown that there was a significant difference (P<0.01) on infection level between transgenics and non-transgenics, and transgenics and controls. It possibly resulted from transgenics that had stronger non-specific immune functions. In addition, fish surface area affected significantly infection level (P<0.001). Carp with larger surface area harboured more parasites for each type of fish, but transgenic with larger surface area than non-transgenics and controls (P<0.01), loaded fewer parasites than others. Besides, the time of infection also greatly influenced (P<0.001) infection level. Results showed that there was a significant decline in parasite infectivity through October to November (P<0.001). It was likely to suggest that there existed senescence resulted in failure of any I. multifiliis isolate maintenance. Significant difference in infectivity between isolate G from grass carp and isolate H from gold fish suggested that different parasite strains may exist. (C) 2009 Elsevier B.V. All rights reserved.

Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati