European Bitterling Rhodeus Amarus Research Articles

Solving the Myxidium rhodei (Myxozoa) puzzle: insights into its phylogeny and host specificity in Cypriniformes.

Myxidium rhodei Léger, 1905 (Cnidaria: Myxozoa) is a kidney-infecting myxosporean that was originally described from the European bitterling Rhodeus amarus. Subsequently, it has been documented based on spore morphology in more than 40 other cypriniform species, with the roach Rutilus rutilus being the most commonly reported host. This study introduces the first comprehensive data assessment of M. rhodei, conducted through morphological, ecological and molecular methods. The morphological and phylogenetic analyses of SSU rDNA sequences of Myxidium isolates obtained from European bitterling and roach did not support parasite conspecificity from these fish. In fact, the roach-infecting isolates represent three distinct parasite species. The first two, M. rutili n. sp. and M. rutilusi n. sp., are closely related cryptic species clustering with other myxosporeans in the freshwater urinary clade, sharing the same tissue tropism. The third one, M. batuevae n. sp., previously assigned to M. cf. rhodei, clustered in the hepatic biliary clade sister to bitterling-infecting M. rhodei. Our examination of diverse cypriniform fishes, coupled with molecular and morphological analyses, allowed us to untangle the cryptic species nature of M. rhodei and discover the existence of novel species. This underscores the largely undiscovered range of myxozoan diversity and highlights the need to incorporate sequence data in diagnosing novel species.

A SHORT NOTE ON WATER QUALITY AND SOME BIODIVERSITY COMPONENTS IN GURBAN VALLEY, GIURGIU COUNTY

Several field trips were carried out in 2022 and 2023, aiming to investigate the water quality parameters, ichthyofaunal and floristic diversity in some areas of Gurban Valley, located in the protected area Natural Park Comana, Giurgiu County, southern Romania. Throughout the study period were identified fish specimens belonging to nine species: Prussian carp Carassius gibelio (Bloch, 1782); Gobio obtusirostris Valenciennes, 1842; Dnieper chub Petroleuciscus borysthenicus (Kessler, 1859); Roach Rutilus rutilus (Linnaeus, 1758); Danubian spined loach Cobitis elongatoides Băcescu & Mayer, 1969; Belica Leucaspius delineatus (Heckel, 1843); Southern ninespine stickleback Pungitius platygaster (Kessler, 1859); European bitterling Rhodeus amarus (Bloch, 1782) and European mudminnow Umbra krameri Walbaum, 1792. A total of 147 captured specimens were measured, weighed and photographed. For the capture of fish, minnow traps and plankton nets were used, on the Gurban River, right tributary of the Neajlov River, Giurgiu County. The floristic inventory compiled so far included 58 plant species grouped into 31 families, with European, circumpolar, Eurasian, eurasiatic continental or cosmopolitan distribution. Related to physico-chemical characterization of water samples collected from four sampling points (SP), the results of laboratory analysis allowed to frame the water into quality classes and to evaluate if the water meets the requirements for aquatic organisms. Hence, on the basis of nitrite-nitrogen (N-NO2-) and nitrate-nitrogen (N-NO3-) water corresponds to Ist quality class, meanwhile chemical oxygen demand (COD), phosphate-phosphorus (P-PO43-) and ammonium-nitrogen (N-NH4+) allowed to associate water quality with IIIrd class. In addition, it has been found very significant correlations between electrical conductivity (EC) and total hardness (TH) with r=0.9230*** and between pH and TH with r=0.8821***, respectively.

Parasites and their impact on thick-shelled river mussels Unio crassus from two populations in Luxembourg.

The thick-shelled river mussel Unio crassus Philipsson, 1788 is a species native to many European habitats, with declining populations. The impact of parasite communities on health status of this species is poorly understood. In this study, parasites of 30 U. crassus specimens from the Our and Sauer Rivers in Luxembourg were identified morphologically and, in some cases, using molecular genetic methods. The findings were correlated to selected parameters (total length, visceral weight, shell lesions, gonadal stage). The 2 populations did not differ in shell length, visceral weight, number of males and females, gonadal scoring, shell lesions, and the occurrence of glochidia. The prevalence and infestation intensities of detected Trichodina sp., Conchophthirus sp., and freshwater mite larvae did not differ between the 2 populations, whereas the prevalence and infestation intensities of mite eggs, nymphs, and adults were significantly higher in the Sauer River. Rhipidocotyle campanula and European bitterling Rhodeus amarus larvae were only present in the Sauer. Histopathology revealed the destruction of the gonads by R. campanula and tissue damage by the mites. The only significant correlation of the selected parameters was a positive correlation between R. amarus occurrence and total length as well as a negative correlation between R. amarus occurrence and gonadal stage. In the Sauer River, 2 mussels were found to be hermaphrodites.

Rearing of Bitterling (Rhodeus amarus) Larvae and Fry under Controlled Conditions for the Restitution of Endangered Populations.

Simple SummaryAmong the many species threatened with extinction and covered by protection of species is bitterling Rhodeus amarus. It belongs to ostracophilic fish that place spawn inside live mussels. Bitterlings, such as mussels, belongs to indicator species that testify to the good state of the natural environment. Supporting the populations of these organisms is a necessity in order to preserve the biodiversity of inland waters, which are subjected to severe anthropopression. The development in advance of a method of reproduction and breeding of bitterling under controlled conditions can ensure their survival in the event of an imbalance in the natural environment. These were the first studies of this type, where after 6.5 months of rearing, sexually mature individuals were obtained. In this way, a suitable stocking material of the bitterling was obtained in order to save the endangered populations.Among the several dozen European freshwater fish species, only European bitterling (Rhodeus amarus Bloch) and Rhodeus meridionalis belong to the group of ostrakophilous fish. The embryonic and larval development of the fish in this reproductive group until the time of the yolk sac resorption takes place in the gill cavity of river mussels (Anodonta sp. or Unio sp.). This paper presents the results of the European bitterling Rhodeus amarus being reared under controlled conditions. Bitterling larvae were caught together with river mussels in the natural environment and subsequently placed in a tank for behavioural observations. Bitterling larvae were seen swimming in the water within a week of placing the bivalves under controlled conditions. The bitterling larvae were 8.6 ± 0.11 mm long when they started to swim actively. The rearing was conducted in water at 20 and 26 ± 0.5 °C and lasted for 6.5 months (200 days) in both variants. Initially, the larvae were fed with live nauplii of Artemia salina and subsequently with fodder. The bitterlings in tanks with water at 26 ± 0.5 °C were 66.2 ± 3.0 mm long and weighed 3389 ± 548 mg. For comparison, bitterlings kept in water at 20 ± 0.5 °C were 64.48 ± 3.4 mm long and weighed 3242 ± 427 mg. No larval malformities or mortality were observed during the larvae and fry rearing. The bitterlings had well-developed secondary sexual characteristics and exhibited pre-spawning behaviour at the end of the rearing. This produced suitable bitterling stocking material to be used in the conservation of small or endangered populations.

Age and Growth of the European Bitterling Rhodeus amarus (Cyprinidae, Actinopterygii) in the Uday and Perevod Rivers (Dnipro basin, Ukraine)

European bitterling age and growth were examined in 2017, 2018, and 2019 in the Uday and Perevod rivers in Pyriatynsky National Park (Poltava region, Ukraine). The population was represented by five age groups (0+ to 4+); specimen age was determined by counting annuli on scales. The annuli were visible and often displayed as irregularities in circuli in the centrolateral part of the scales. Standard specimen length varied from 14 to 51 mm; weight varied from 0.09 to 2.5 g. The length-weight relationship was W = 0.00005*TL2.78; W♂ = 0.00048*TL2.18; W♀ = 0.00028*TL2.32 for both sexes, males and females, respectively. The sex ratio was 1:1.26. The most abundant group in the samples from the Uday were young-of-the-years, and 1+ fish in the samples from the Perevod. As for mature specimens, 3+ fish predominated in both samples. The fastest relative growth was during the second year of life.

Microcondylaea bonellii as a new host for the European bitterling Rhodeus amarus

We report for the first time that the freshwater mussel Microcondylaea bonellii (Férussac, 1827) functions as a suitable host for the European bitterling Rhodeus amarus (Bloch, 1782). Given the recent expansion of R. amarus in Europe, the possible physiological cost (e.g. competition for oxygen, reduction in water circulation, and consequent impairment of filter-feeding) of this interaction may further affect the already poor conservation status of M. bonellii populations.

Intensity-dependent energetic costs in a reciprocal parasitic relationship

Parasitic infections elicit host defences that pose energetic trade-offs with other fitness-related traits. Bitterling fishes and unionid mussels are involved in a two-way parasitic interaction. Bitterling exploit mussels by ovipositing into their gills. In turn, mussel larvae (glochidia) develop on the epidermis and gills of fish. Hosts have evolved behavioural responses to reduce parasite load, suggesting that glochidia and bitterling parasitism are costly. We examined the energetic cost of parasitism on both sides of this relationship. We used intermittent flow-through respirometry to measure (1) standard metabolic rate (SMR) of individual duck mussels Anodonta anatina (a common bitterling host) before and during infection by embryos of the European bitterling Rhodeus amarus, and (2) SMR and maximum oxygen uptake (MO2max) of individual R. amarus before and during infection with glochidia of the Chinese pond mussel Sinanodonta woodiana (a mussel species that successfully infects bitterling). As predicted, we observed an increase in mussel SMR when infected by bitterling embryos and an increased SMR in glochidia-infected bitterling, though this was significantly mediated by the time post-infection. Contrary to our predictions, glochidia infection did not impair MO2max and the number of glochidia attached to gills positively (rather than negatively) correlated with MO2max. The results suggest that tolerance is the prevailing coping mechanism for both fish and mussels when infected, while resistance mechanisms appear to be confined to the behavioural level.

The endangered thick-shelled river mussel (Unio crassus): a new host species for the European bitterling (Rhodeus amarus)

Large freshwater mussels (Unionoida) are declining throughout the world. The European bitterling Rhodeus amarus (Bloch, 1782) female spawns its eggs inside the unionids’ shells, where fertilisation and further embryonic development take place; thus its reproduction depends fully on the presence of large freshwater mussels. Unio crassus, previously regarded as one of the most numerous unionids in Europe, is now listed in the IUCN Red Data List as being globally endangered. Despite its previous prevalence, it was never reported as a host for the bitterling. A large population of U. crassus was studied in small river at the Świętokrzyskie Mts (Poland), where also electrofishing was conducted. In each bitterling territory located on the study plots, we found individuals of U. crassus, with the bitterling eggs or larvae developing on mussel’s gills. That proves that this species can be also used by the bitterling for reproduction. We suggest that this relationship has not been reported to date due to the mussels’ rarity and ongoing decline. However, it is also possible that the endangered mussel is a novel host for the bitterling, which is expanding its range throughout Europe.

Methodological issues affecting the study of fish parasites. III. Effect of fish preservation method.

The aim of this study was to evaluate the influence of preservation method on the results of parasite community studies. Two host species, European perch Perca fluviatilis and European bitterling Rhodeus amarus, were examined for parasites after having been subjected to 4 different storage treatments: freezing, preservation in 4% formaldehyde or 70% ethanol and transportation of live (fresh) fish as a control. Preservation prior to dissection resulted in a loss of information, leading to incomplete quantitative data (all preservation treatments), qualitative data (ethanol and formaldehyde preservation) and a lowered ability to determine parasites to species level based on morphology compared to dissecting fresh fish. Of the more abundant taxa, only crustaceans and acanthocephalans provided relatively even results between treatments. We conclude that preservation media, such as ethanol or formaldehyde, significantly affects the ability to obtain precise parasite community data; hence, we recommend the use of freshly sacrificed fish for parasite community studies whenever possible. Alternatively, freezing may prove acceptable for evaluating parasite community taxonomic composition.

Experimental evidence for parasite-induced over-winter mortality in juvenile Rhodeus amarus.

In this study, the effects of the eye fluke Diplostomum pseudospathaceum (Trematoda) infection on over-winter survival of young-of-the-year (YOY) European bitterling Rhodeus amarus (Cyprinidae) were examined between September 2010 and April 2011. The fish were reared in semi-natural conditions to ensure that results were not confounded by other parasite infections. The cumulative mortality of R. amarus from November until April was significantly higher in D. pseudospathaceum-infected fish (57·3%) compared to controls (42·1%). Infection of the parental generation did not have any effect on the mortality of juveniles. The results indicate that D. pseudospathaceum infection increases over-winter mortality of YOY R. amarus. The possible mechanisms causing mortality are discussed.

Overwinter body condition, mortality and parasite infection in two size classes of 0+ year juvenile European bitterling Rhodeus amarus

Body condition and parasite abundance were examined in two size classes of European bitterling Rhodeus amarus during the first overwintering period in two seasons (2007-2008 and 2009-2010). Body condition of large fish did not change during winter, and increased significantly in March. From November to February, small fish showed a decreasing trend in condition. Despite a significant increase in March condition of small fish only reached the same level as before winter. Total parasite abundance increased significantly in winter in both fish size classes, reflecting a seasonal increase in monogenean infection. Large fish were parasitized significantly more than small fish during winter, but only in small fish was a negative correlation between parasite infection and condition found and a significant decrease in parasite abundance recorded after wintering, indicating mortality of heavily infected individuals with low condition during the winter. A trend for higher overwinter mortality in small fish was found under semi-experimental conditions. The decrease in condition during the winter period in small fish may reflect faster energy depletion generally expected in smaller individuals. The results indicate that parasite infection may contribute to the overwinter mortality of 0+ year R. amarus, with a stronger effect in smaller individuals.

Reproduction mode of European Bitterling (Rhodeus amarus,Bloch, 1782) determined through rapid oocyte counts and size determination using digital imaging

Summary This study focuses on assessing the reproduction mode of an important model species for evolutionary and behavioural ecology by using digital image analysis: the European bitterling Rhodeus amarus (Bloch, 1782). Specifications of mode of reproduction were determined using oocyte size distribution, seasonal dynamics in mean oocyte diameter and total number of oocytes in ovary samples gained from April to July 2007. The rapid oocyte count was enabled by using lucia image analysis software, which also provided measurement and colour estimations of oocytes. Bitterling ovaries showed features typical for indeterminate spawners, i.e. a continuous distribution of oocyte size over the reproductive season and recruitment of new pre-vitelogenic oocytes in the second half of the reproductive season. These results are consistent with the view that the European bitterling is a batch spawning fish with indeterminate fecundity.

The role of the European bitterling (Rhodeus amarus, Cyprinidae) in parasite accumulation and transmission in riverine ecosystems

In aquatic ecosystems, fish play a key role in parasite accumulation and transmission to predacious animals. In the present study, realized on seven populations of a small cyprinid fish species, the European bitterling Rhodeus amarus, we investigated (1) the role of the European bitterling as a potential intermediate or paratenic host, (2) the ability of the fish to accumulate parasites with similar final host group, and (3) its significance as a potential source of parasite infection in the ecosystem in respect to habitat characteristics. A total of 36 parasite species were recorded; 31 species (90% of all parasite specimens) were classified as endoparasites. Most of the endoparasites were found in the larval life stage, using bitterling as an intermediate or paratenic host. In particular, parasite community structure showed significantly higher proportions of allogenic parasites in comparison with autogenic. The supposed co-occurrence of parasite species with identical final host groups showed only a weak association. The adjacent reservoir areas were a significant determinant of both the total and infracommunity parasite species richness and for the mean parasite abundance. No relationship between the distance of sampling site from the adjacent reservoir and parasite community characteristics was found. As a small-sized fish with a wide distribution range and high local abundances, the European bitterling can represent a natural prey for a wide range of piscivorous predators. Due to its susceptibility to the number of larval endoparasites, this fish species may therefore fulfill the role as important transmitter of parasites to their final hosts.

Seasonal dynamics in population characteristics of European bitterling Rhodeus amarus in a small lowland river

The seasonal dynamics of biological traits in a population of European bitterling Rhodeus amarus from a small river in central Europe (River Kyjovka, Czech Republic) were investigated from April 2007 to March 2008. The reproductive season lasted from early April to mid-June, with a peak in late April when > 50% of females possessed ripe eggs in their ovaries. The sex ratio was female-biased, with a higher bias following the peak in reproduction, suggesting higher mortality of males than females over the reproductive period. The population was effectively annual, with a major decrease in adult fish abundance at the end of the reproductive period. Highest relative lipid content and condition factor were observed in February, both decreasing with an increase in investment into gonads. Seasonal dynamics in somatic condition, relative lipid content and gonad mass, and their comparison with other R. amarus populations, suggest that the study population allocated a disproportionally high level of resources to reproduction.

A morphological and genetic analysis of the European bitterling species complex

Bitterling fishes lay their eggs on the gills of living freshwater mussels and are valuable models in behavioural and evolutionary ecology. We used morphological and genetic data to resolve the taxonomic relationships of bitterling in Europe. Previous studies have suggested the European bitterling is either a single species with a wide but discontinuous geographic distribution, or a complex of species. Morphometric and meristic data identified differences between three putative species; with a clear distinction between the eastern Asian Rhodeus sericeus, western European bitterling Rhodeus amarus, and colchian bitterling, Rhodeus colchicus. Polymorphism in the mitochondrial DNA control region was predominantly due to insertion/deletion events, making phylogenetic inference difficult, but the single haplotype found in R. sericeus populations was detected at low frequency (one of 24 individuals) in R. amarus and R. colchicus populations. Eight control region haplotypes were found in R. amarus populations, which were distinct from the two haplotypes in a R. colchicus population. Cytochrome b data produced a phylogeny with strongly-supported differentiation between a clade of two R. sericeus haplotypes and a clade of six R. amarus/colchicus haplotypes. The star-like topology of the R. amarus/colchicus haplotypes in a minimum spanning network suggested a rapid radiation in this clade. Our results are consistent with an hypothesis of relatively ancient divergence of R. sericeus from R. amarus/colchicus and more recent and rapid differentiation between R. amarus and R. colchicus. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 337–347.

Classical and molecular cytogenetic characterization of allochthonous European bitterling Rhodeus amarus (Cyprinidae, Acheilognathinae) from Northern Italy

A cytogenetical study was carried out on 34 specimens of the European bitterling Rhodeus amarus (Teleostei: Cyprinidae, Acheilognathinae) from four rivers of the Venice district (NE Italy). This allochthonous fish species was accidentally introduced in the North-East of Italy about 20 years ago and is now rapidly spreading all over the rivers of the Northern part of the country. All the studied specimens are characterised by the same karyotype (2n = 48: 8M + 20SM + 20ST), i.e., the typical one of the native populations of the species. However, a polymorphism in the number of NOR bearing chromosomes has been found. In fact, in addition to the main species-specific NORs, on the short arms of chromosome pair 7, two to five additional 18S rDNA sites have been revealed by FISH in different specimens. Sequential staining with silver nitrate, chromomycin A(3) and DAPI revealed that most of the additional sites are inactive and CMA(3)-positive. Data herein reported confirm that in spite of an overall morphological karyological conservativeness, significant differences for the finer cytogenetic features can be found within the Acheilognathinae with the 2n = 48 and NF = 76 karyotype.

Deceptive female oviposition behaviour elicits male ejaculation in the European bitterling

In European bitterling Rhodeus amarus, fish that lay their eggs in the gill chambers of living freshwater mussels, females perform conspicuous behaviours associated with spawning that increases the probability of males performing ejaculatory behaviour and participating in a spawning. A significant positive association was detected between behaviour in which a female performs a spawning action but without releasing eggs, here termed ‘deceptive female oviposition’, and ejaculatory behaviour by courting males.

A possible evolutionary lag in the relationship between freshwater mussels and European bitterling

The coevolutionary dynamics between European bitterlingRhodeus amarusand freshwater unionid mussels, which the former parasitize by laying eggs on their gills, were tested. In a series of experiments fish preferences and mussel responses were compared in parasites and hosts of recent (Europe) and ancient (Asia) sympatry.Rhodeus amarusreadily oviposited on the gills of all mussel species tested. Fish that laid their eggs on the gills of AsianAnodonta woodiana,however, suffered a dramatic reduction in reproductive success compared to fish that oviposited on the gills of European mussels:Unio pictorum,Unio tumidus,Anodonta anatinaandAnodonta cygnea. This difference was the result of egg ejection behaviour by mussels rather than the unsuitability of the internal gill environment for European bitterling embryo development. The ejection response of mussels with a long sympatry with European bitterling was considerably more pronounced than that of mussels with a substantially shorter sympatry. The data support a coevolutionary arms race between bitterling and mussels and point to an evolutionary lag in the relationship betweenR. amarusand its European mussel hosts.

Characteristics of the European Bitterling Rhodeus amarus (Cyprinidae) in the Rihios River, Greece

ABSTRACT We sampled the population of the European bitterling Rhodeus amarus (Bloch, 1782) from the Rihios River (Greece) monthly between September 1997 and January 1999. The overall sex ratio of females to males was 1:2.14 and was statistically different from unity. The total length of the individuals caught varied from 12 to 83 mm. The population of the Rihios River grew allometrically and had a five-year life cycle. The parameters of the von Bertalanffy growth curves were estimated as L∞= 120.25 mm, k= 0.86/year, and t0= 0.22 years. The condition factor and the gonadosomatic index indicated that reproduction occurred around April-June. Fecundity was low with a few but relatively large eggs produced. Natural mortality was 0.60/year. The diet of bitterling consisted of algae, insects, crustaceans, and organic and inorganic material.