Development of Myxobolus bramae (Myxosporea: Myxobolidae) in an oligochaete alternate host, Tubifex tubifex

The development of Myxobolus bramae Reuss 1906, a myxosporean parasite of the gills of common bream Abramis brama L., was studied in experimentally infected oligochaetes. In five experiments, uninfected Tubifex tubifex (Müller) and Limnodrilus hoffmeisteri Claparéde were exposed to mature myxospores of M. bramae . In four experiments triactinomyxon type actinospores developed in Tubifex specimens but no infection was found in Limnodrilus . Actinospores were released from oligochaetes 70–81 days after initial exposure. At that time pansporocysts containing eight actinospores were located in the gut epithelium of experimental oligochaetes, but free actinosporean stages were also found in their gut lumen. Each actinospore had three pyriform polar capsules and a barrel-shaped sporoplasm with 32 secondary cells. The spore body joined the three caudal projections with a stout style. The total length of the actinospore was 139 μm on the average.     

Experimental identification of the actinosporean stage of Sphaerospora renicola Dykova & Lom 1982 (Myxosporea: Sphaerosporidae) in oligochaete alternate hosts

The extrapiscine development of Sphaerospora renicola, a myxosporean parasite of the kidney of common carp, Cyprinus carpio L., was studied in the experimentally infected oligochaetes Tubifex tubifex (Müller) and Branchiura sowerbyi (Beddard). After the infection of these tubificids with homogenized common carp kidneys containing myxospores of S. renicola, the development of actinosporean stages was first observed under light microscopy 8 days after infection in pathogen-free T. tubifex. Infection of B. sowerbyi with mature actinosporean stages was first observed 91 days after infection. At that stage of development, pansporocysts containing neoactinospores filled the intestinal epithelium of the worm. Ninety-five days after infection, pansporocysts containing actinospores and free actinospores were found in the gut lumen of B. sowerbyi. Actinospores of S. renicola emerged from B. sowerbyi after 98 days of intraoligochaete development. These were floating in the water and showed the typical form of neoactinospores. The shape of the spores was triangular in apical view and elliptical in lateral view. The prevalence of infection reached 37%. Control specimens of B. sowerbyi proved to be free of neoactinospores. Except for a single specimen of B. sowerbyi, the only early developmental stages (pansporocysts) were found in T. tubifex.     

Dynamics of experimental production of Thelohanellus hovorkai (Myxozoa: Myxosporea) in fish and oligochaete alternate hosts

The dynamics of development and production of Thelohanellus hovorkai (Myxozoa) were examined to investigate factors inducing haemorrhagic thelohanellosis in carp, Cyprinus carpio L. Fresh actinospores of T. hovorkai were harvested from the oligochaete alternate host, Branchiura sowerbyi, and used for infection experiments with myxosporean-free carp. Visualization of actinospores by fluorescent labelling revealed that sporoplasms penetrated the gill filaments of carp immersed in an actinospore suspension as early as 30 min post-exposure (PE). Plasmodia of T. hovorkai developed in the connective tissues of various organs and matured 3-5 weeks PE; dispersion of myxospores from degenerate plasmodia occurred 5-7 weeks PE. Challenges with a high dose of actinospores (4.5 x 10(6) spores per fish) resulted in the onset of disease, which was more easily achieved by the oral intubation of actinospores than by immersion in an actinospore suspension. Actinosporean-free B. sowerbyi were exposed to different densities of myxospores (10(4)-10(6) spores per oligochaete) and subsequently reared at different temperatures (15, 20, 25 degrees C). At 20 and 25 degrees C, actinospore releases were first detected 40-43 days PE, with multiple peaks of release (max. 7 x 10(5) actinospores day(-1)) during the next 60 days. We concluded that the developmental cycle of T. hovorkai was completed within 3-5 months at 20-25 degrees C, and that the ingestion of large numbers of actinospores orally, possibly by feeding on infected oligochaetes, resulted in a disease condition in carp.     

The life cycle of Chloromyxum auratum (Myxozoa) from goldfish, Carassius auratus (L.), involves an antonactinomyxon actinospore

The myxozoan parasite Chloromyxum auratum Hallett, Atkinson, Holt, Banner & Bartholomew, 2006 , was shown experimentally to have a two‐host life cycle which involved a previously undescribed antonactinomyxon actinospore stage. Myxospores obtained from gall bladders of naturally infected feral goldfish, Carassius auratus (L.), were used to infect samples of mixed species of oligochaete worms obtained from the same locality as the fish: Fern Ridge Dam, Oregon, USA. After some 110 days post‐exposure, actinospores were detected from the water above the oligochaetes. The 18S rDNA sequence of these actinospores was identical to the original myxospores. Spore release was sporadic, of low intensity and short duration, which confounded efforts to identify the host oligochaete species and infect naïve fish. This is the first life cycle that incorporates an actinospore of the collective group Antonactinomyxon, and the first life cycle demonstrated in the laboratory for a species of Chloromyxum.     

The susceptibility of diverse species of cultured oligochaetes to the fish parasite Myxobolus pseudodispar Gorbunova (Myxozoa)

This study provides detailed information on the invertebrate hosts of Myxobolus pseudodispar (Myxozoa) and explores the susceptibility range of several species and analyses the relevance of the species composition of an oligochaete population. Our findings demonstrate that the oligochaete host range of M. pseudodispar is similarly wide as the number of vertebrate host species. Besides Tubifex tubifex and Limnodrilus hoffmeisteri, Psammoryctides barbatus and Psammoryctides moravicus were also found to be susceptible invertebrate hosts. The genetic characterization of the mitochondrial 16S rDNA of T. tubifex sensu lato revealed that lineages I, II and III are susceptible to M. pseudodispar, whereas T. tubifex lineage VI seems to be non‐susceptible. T. tubifex lineage V and L. hoffmeisteri specimens were positive in a M. pseudodispar‐specific PCR, but in most cases, the release of mature actinospores could not be detected. Hence, these non‐susceptible oligochaetes likely serve as `biological filters` as they remove myxospores from the sediment without producing actinospores. Together with the phylogenetic analysis of the susceptible and non‐susceptible oligochaete hosts on the basis of mt 16S rDNA sequences, the route of the development of M. pseudodispar in the oligochaete hosts was tracked by in situ hybridization. According to our findings, the gut epithelia seem to be a portal of entry of the sporoplasms, where the development of the parasite also takes place. The basal lamina seems to be involved in the migration of the parasite, and the worm’s cellular immune response is activated by the infection.     

Development of a rapid assay for the diagnosis of Myxobolus cerebralis in fish and oligochaetes using loop-mediated isothermal amplification

A loop-mediated isothermal amplification assay was developed for the rapid detection of Myxobolus cerebralis in both fish and oligochaete hosts. The assay was optimized to amplify parasitic DNA by incubation with Bst DNA polymerase and a set of six specially constructed primers at 65 degrees C for 60 min. The amplification products were detected visually using SYBR Green I dye which gave identical results to gel electrophoresis analysis. Parasite DNA was detected from infected oligochaetes, and from the anal fin, caudal fin, dorsal fin and operculum of clinically infected fish. This 'Myxo-LAMP' assay has a detection limit similar to that of a polymerase chain reaction assay (10(-6)), but is more rapid and only requires a water bath for amplification and is therefore practical for simple and rapid diagnosis of infected tissue.     

The life cycle of Henneguya nuesslini Schuberg & Schroder, 1905 (Myxozoa) involves a triactinomyxon-type actinospore

The life cycle of the histozoic myxozoan parasite Henneguya nuesslini was investigated in two salmonid host species. Naive brown trout, Salmo trutta, and brook trout, Salvelinus fontinalis, were experimentally infected in two trials by triactinomyxon type actinospores from naturally infected Tubifex tubifex. In exposed common carp, Cyprinus carpio, no myxospore production was detected. The parasite formed cysts with mature myxospores in the connective tissue of the fish 102 days post-exposure. The morphology of both actinosporean and myxosporean stages was described by light microscopy and a 1417-bp fragment of the 18S rDNA gene was sequenced. Sequence analysis confirmed the absolute congruence of the two developmental stages and assisted in determining species identity. Host range, tissue specificity and myxospore measurements provided sufficiently distinctive features to confirm species validity and were thus crucial for identification. The triactinomyxon spores had 16 secondary germ cells, unique dimensions, a very opaque sporoplasm matrix and three conspicuously protruding, pyriform polar capsules. This is the first record of a Henneguya sp. life cycle with a triactinomyxon-type actinospore, which suggests a close relationship with the Myxobolus group and a polyphyletic origin of the genus Henneguya.     

Macrophage or fibroblast-conditioned medium potentiates Growth of Trypanosoma danilewskyi Laveran & Mesnil 1904

Little is known about the role of macrophage products in blood-borne parasitic infections of fish. This study determined the effects of soluble products of goldfish macrophages on the growth of the haemoflagellate, Trypanosoma danilewskyi Laveran & Mesnil. Cell-free supernatants were collected from macrophage cultures that were derived from infected or uninfected goldfish. Trypanosomes were seeded into wells containing conditioned or control medium, incubated for seven days, and enumerated using flow cytometry. Supernatants collected from macrophages isolated from infected or uninfected fish, supported parasite growth significantly better ( P < 0.05) compared to control medium. Supernatants, collected on day 12, 15, and 18 from macrophage cultures, induced a greater than 25% increase in the number of parasites. Moreover, the growth of T. danilewskyi was related to the number of macrophages seeded into cultures. This growth-enhancing activity was not specific to species or cell-type, as medium conditioned by mammalian macrophages or fibroblasts (fish or mammalian) significantly enhanced ( P < 0.05) parasite growth. While compound(s) that are necessary for proliferation remain unidentified, our results suggest that over the prolonged evolutionary relationship with teleosts, T. danilewskyi has evolved to utilize soluble products of macrophages and fibroblasts as growth-enhancing factors.     

An assessment of the variation in the prevalence of renal myxosporidiosis and hepatitis in wild brown trout, Salmo trutta L., within and between rivers in South-West England

The prevalence of renal myxosporidiosis in wild brown trout, Salmo trutta, in seven river catchments in South-West England was investigated. Three hundred and twenty-seven fish were sampled from 16 sites, of which 54 (16.5%) were found, by histological examination of the kidney, to be infected with Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease. No T. bryosalmonae infected fish were found in one river catchment, in other catchments the prevalence ranged from 2.5% to 36%. Hepatitis was strongly associated with the presence of T. bryosalmonae (odds ratio = 20.2, P < 0.001). Chloromyxum schurovi was found in 25% of fish and in six of seven river catchments, where the prevalence ranged from 2.4% to 63%. There was a strong negative association between the presence of T. bryosalmonae and C. schurovi (odds ratio = 0.10, P < 0.001). A hierarchical binomal model of the variance indicated that for T. bryosalmonae most of the variance existed at the site level, whereas for C. schurovi most variance existed at the river catchment level, suggesting that prevalence of T. bryosalmonae infection is determined largely by site level factors (e.g. presence of alternate host). The intraclass correlation coefficients (ICC) were 0.2 and 0.4 for T. bryosalmonae and C. schurovi, respectively, indicating the latter has higher effective transmission because of a higher level of infectiousness and/or abundance of alternate oligochaete hosts. These values can be used in future studies to estimate the sample sizes required to generate prevalence estimates with the required precision.     

Humoral immune response of turbot, Scophthalmus maximus (L.), to antigens from Tetramicra brevifilum Matthews & Matthews, 1980 (Microspora)

Abstract. The humoral immune response of turbot, Scophthalmus maximus (L.), to antigens from the microsporean parasite Tetramicra brevifilum Matthews & Matthews, 1980, was studied. Thirty days after intraperitoneal immunization with whole T. brevifilum spores in Freund's complete adjuvant, double indirect ELISA indicated that initial production of antibodies to parasite surface antigens was considerably higher than production of antibodies to the antigens contained in a crude extract (CE) of spores. Following re-immunization without adjuvant on day 30, levels of antibodies to surface antigens gradually declined, whilst levels of antibodies to CE antigens increased. The antibody response of intraperitoneally immunized fish was characterized by Western blotting of total soluble antigens obtained by heating and reduction of T. brevifilum spores at 95–100°C in Tris-HCl buffer containing SDS and dithiothreitol: a series of bands with molecular weights between 20 and 53 kDa was recognized by immunized turbot sera. Four additional bands (with molecular weights between 15 and 18kdA) were recognized by serum from re-immunized fish. ELISA studies of sera from naturally infected fish revealed a surprisingly low incidence of strong T. brevifilum seropositivity (61% individuals); antibodies to surface antigens predominated in seropositive individuals. The low background response levels and high sensitivity of the ELISA used in this study indicate that the assay is of value for the monitoring of serum antibody levels in turbot. However, given the relatively low seropositivities observed in naturally infected turbot, particularly to CE antigens, the use of anti- T. brevifilum serum antibody levels for the diagnosis of infection by this parasite may lead to false negative results.     

Parasitism, condition and number of front head breeding tubercles in roach (Rutilus rutilus L.)

Abstract –  In a previous study on the male roach, Rutilus rutilus , we found a positive correlation between sexual ornamentation, breeding tubercles (BTs) on lateral sides and parasite resistance. As a continuation of that study, we examined another measure of sexual ornamentation – number of BTs on front head – of male roach from five populations. BTs on head correlated positively with fish size in two populations and with condition in one population, but not with parasite resistance (proportion of dead parasites) in any of the populations. Moreover, head BTs correlated negatively with the number of two parasite species ( Rhipidocotyle campanula and Myxobolus mülleri ) in two populations, but positively with the number of a third parasite ( Raphidascarus acus ) in one population. In addition, a negative correlation with spleen size was found in one population. The present results suggest that head BTs of male roach – although the patterns vary between populations – may signal condition and parasite load, but not resistance, in contrast to lateral BTs. Therefore, our results are in line with the hypothesis of multiple-message sexual ornaments.     

Efficacy of different types of live and non-conventional diets in endangered clown knife fish Chitala chitala (Hamilton-Buchanan) during its early life stages

In the present study, the growth and survival of early life stages (ELS) of Chitala chitala were studied in nylon hapa for 28 days, followed by rearing in fibreglass reinforcement plastic (FRP) tanks for a period of 30 days. Ten‐day‐old ELS of C. chitala reared in hapa were fed with three different diets namely Indian Major Carp (IMC) spawn (<8 mm), live tubifex and fresh fish eggs. In the second phase, 28‐day‐old ELS were stocked in 200‐lit FRP tank and supplied four different live diets namely live tubifex worm, chironomous larvae, zooplanktons and mosquito larvae. Fish accepted all types of diets in the experimental rearing period in both the systems. The experiments conducted in hapa showed a higher specific growth rate (SGR), weight gain per cent and survival rate in larvae fed with live tubifex (SGR=1.76±0.02) than fish eggs (0.77±0.31) and IMC spawn (0.46±0.12). The study carried out in FRP tanks revealed that SGR was higher in ELS fed on chironomous larvae (4.44±0.61), followed by mosquito larvae (3.29±0.40) and live tubifex (3.28±0.36), whereas minimum SGR was recorded with zooplanktons (2.84±0.66). A significant difference (P<0.05) in SGR, final mean weight and weight gain (%) was also recorded. The highest mean survival rate (100%) of ELS in an FRP tank was observed in chironomous larvae and zooplanktons, whereas with live tubifex and mosquito larvae the same survival rate (80%) was recorded. The rate of survival of the ELS reared in hapa varied from 65% to 85%. The experiments showed that ELS of C. chitala could be reared successfully in hapas and fibreglass reinforcement tanks for attaining better survivability and growth.     

Studies on the proposed role of Tubifex tubifex (Muller) as an intermediate host in the life cycle of Myxosoma cerebralis (Hofer, 1903)

Abstract. In a recently proposed hypothesis for the transmission of Myxosoma cerebralis , the causative agent of salmonid whirling disease, it was suggested that there was a developmental cycle in tubificid worms culminating in actinosporean spores, which were infective to the fish. Results are presented here which do not support the actinosporean involvement in the life cycle. On addition of M. cerebralis spores to Tubifex tubifex colonized in sterilized medium, no significant change in the prevalence of Triactinomyxon dubium (i.e. T. gyrosalmo ) was found. Although it is shown that these worms are capable of ingesting M. cerebralis spores, neither hatching of the spores nor further development within the worm has been observed. Field observations on the distribution of actinosporean species show no obvious correlation between the occurrence of T. dubium and M. cerebralis .     

Performance of different types of diets on experimental larval rearing of endangered Chitala chitala (Hamilton) in recirculatory system

This is the first report on the successful larval rearing of captive bred population of Chitala chitala (Hamilton). C. chitala is one of the endangered fresh water fish species in India for which the development of controlled larval rearing procedures are needed for stock enhancement. Fifteen days old post-hatchlings were stocked for 28 d in a 30 L recirculatory tanks using eight different diets i.e. live feed (tubifex worms, chironomous larvae, zooplanktons,), dry feed (dry tubifex, spirulina, daphnia) and other non-conventional feed (fish eggs and boiled egg-yolk). Fishes accepted all types of diets. The study revealed that specific growth rate (SGR) was higher in post-hatchlings fed on live tubifex worms (2.40 ± 0.72) followed by fish eggs (2.15 ± 0.71), dry tubifex (2.12 ± 0.40), chironomous larvae (1.91 ± 0.44), spirulina (1.79 ± 0.38), daphnia (1.42 ± 0.79) and planktons (1.37 ± 0.77) whereas minimum SGR was recorded with boiled egg-yolk (0.63 ± 0.5). A highly significant difference (p < 0.01) in SGR was observed in fish fed on live feed (tubifex worms, chironomous larvae, planktons, spirulina), dry tubifex and fish eggs whereas for daphnia and boiled egg-yolk it was only significant (p < 0.05). The final mean weight and weight gain showed highly significant difference (p < 0.01) in live tubifex, zooplanktons, spirulina, chironomous larvae, dry tubifex and fish eggs, whereas daphnia and boiled egg-yolk fed larvae showed significant difference (p < 0.05). Highest mean survival rate on day 28 was observed in live tubifex worms (94%) and chironomous larvae (92%). The post-hatchlings reared with spirulina and daphnia showed same survival rate of 88% whereas the lowest mean survival of 66% was recorded in boiled egg-yolk. The experiments showed that captive bred post-hatchlings of C.chitala could be reared in experimental recirculatory system for attaining higher growth and survival during early life stages. However, methods to improve the larval rearing have to be improved further for commercial farming of the species.     

Characterization of glycans in the developmental stages of Myxobolus cerebralis (Myxozoa), the causative agent of whirling disease

Glycans and sugar-binding molecules (lectins) form an interactive recognition system, which may enable parasitic organisms to adhere to host cells and migrate into target tissues. The aim of the present study was to analyse surface-associated glycans in the developmental stages of Myxobolus cerebralis (Hofer), the causative agent of whirling disease. A panel of biotin-labelled plant lectins was used to detect a broad spectrum of glycan motifs with high specificity. Binding sites were detected histochemically in the tissue sections of infected rainbow trout, Oncorhynchus mykiss (Walbaum), and infected Tubifex tubifex (Müller), and were characterized by light, fluorescence and transmission electron microscopy. With mannose-specific lectins [Lens culinaris agglutinin, Pisum sativum agglutinin, Canavalia ensiformis agglutinin (LCA, PSA, CanA)] mannose-containing glycans were detected in all the developmental stages and host tissues. No binding sites for galactose-specific lectins were present in M. cerebralis spores but reactivity with host tissues occurred. Diversity in glycans was detected by N-acetyl-D-galactosamine-specific lectins in sporoplasm cells of M. cerebralis and triactinomyxon spores. In the group of lectins with monosaccharide-specificity for N-acetyl-D-glucosamine (GlcNAc), the reactivity of Datura stramonium agglutinin (DSA), Lycopersicon esculentum agglutinin (LEA) and Solanum tuberosum agglutinin (STA) was restricted to polar capsules whereas Griffonia simplicifolia agglutinin II (GSA II) also bound to sporoplasm cells of stages in the fish host but not in those present in infected T. tubifex. Moreover, Triticum vulgaris (wheat germ) agglutinin (WGA) and succinylated WGA indicated the presence of N-acetyl-D-glucosamine polymers in polar capsules. No specificity for spores was observed concerning 'bisected'N-glycans and no reactivity in parasitic stages was observed with the fucose-binding lectin Ulex europaeus agglutinin (UEA) I, Sambucus nigra agglutinin (SNA) (specific for alpha2,6-sialylated glycans) and Maackia amurensis agglutinin (MAAI) (specific for alpha2,3-sialylated glycans). Arachis hypogaea (peanut) agglutinin (PNA), Erythrina cristagalli agglutinin (ECA), GSA I, Sophora japonica agglutinin (SJA), Dolichos biflorus agglutinin (DBA) and GSA II detected reactive sites solely confined to the developmental stages of M. cerebralis and were not reactive in the fish host. These parasite-specific glycans may play a role in the adhesion process of the parasite to fish epidermis prior to infection, but may provide protection to the host by activating the complement system, or stimulating an adaptive immune response as putative antigens.     

Histopathological and ecological aspects of Henneguya and Myxobolus (Myxosporea) infections in Acanthopagrus australis (Günther) (Pisces: Sparidae) from Moreton Bay, Australia

Abstract. Sporulated plasmodia of Henneguya sp. infected the gill filaments, interhemibranch septum, gut and other microhabitats of Acanthopagrus australis in Moreton Bay, southern Queensland, whereas Myxobolus sp. infected only the gut. There was usually no inflammatory response, but some plasmodia in the gill filaments were associated with a granulomatous, predominantly lymphoid, response that was not determined by either parasite maturity, or sex and size of fish or season. There was a microhabitat shift in branchial Henneguya infection from predominantly gill filament in juvenile bream to gill septum in older fish. The highest prevalences of Henneguya were in the southern part of Moreton Bay, but trends in seasonal infection and prevalences in relation to size and sex of fish were similar in the western and southern parts of the bay. This suggested a widespread distribution of the putative annelid alternate host in Moreton Bay, with highest densities in the southern part. Myxobolus infection was most prevalent in young male fish at the winter spawning grounds on eastern surf bars.     

Eimeria scardinii Pellérdy and Molnár, 1968 in the kidneys of Rutilus rutilus (L,) and Scardinius erythrophthalmus (L.) from northern Greece

Abstract. The occurrence of Eimeria scardinii in roach, Rutilus rutilus (L.), and rudd, Scardinius erythrophthalmus (L.), from a lake in northern Greece is reported. The coccidium was found in the renal haemopoiettc tissue, mainly in the form of mature sporulated oocysts. The morphology and dimensions of the parasite, as well as the host reaction, were very similar in both species of fish examined. The overall prevalence of infection in roach and rudd was 6·67% and 6·3%, respectively. The prevalence of infection of roach was higher during summer (22·22%) but less than 5% in other seasons.     

Loxothylacus ihlei Boschma, (Rhizocephala) and its effects on the mud crab, Scylla serrata (Forskål), in northern Australia

Abstract. Loxothylacus ihlei , a rhizocephalan parasite of the mud crab, Scylla serrata (Forskål), is reported for the first time in Australian waters. The parasite is described and found to be variable in a number of characters. Most infected S. serrata , collected from commercial catches in the Northern Territory, Australia, were significantly smaller than uninfected crabs, and their abdominal flaps were relatively larger than those of mature females. Annual prevalence of infection was low (2.1%), with the monthly variation ranging from negligible early in the year to around 7% in November.     

The significance of myxosporean infections in roach, Rutilus rutilus L., in different habitats

Abstract. Two Myxobolus species, M. pseudodispar and M. ellipsoides , and two Myxidium species, M. rhodei and M. pfeifferi , were found in roach, Rutilus rutilus L., from three different locations in northern Greece, northern England and Scotland. Their prevalence, distribution in the host and pathology were studied. In the ease of M. rhodei , the pathological changes were quantitatively evaluated by computer-based image analysis, and the results expressed in terms of area and volume of organs affected. The pathology of M. pfeifferi was associated with trophozoites in the bile duets and the infection ranged from mild to severe. In the severe eases, degeneration of duetal mucosa sometimes progressed to focal hepatitis. Myxidium rhodei was found in the kidneys as large cysts containing mature and immature spores (Type A cysts), and less often, in the form of small concentric cysts (Type B) which contained no obvious spores but which were characterized by a marked host response giving the appearance of focal granulomas. Type A cysts were also found in liver and spleen, and Type B cysts in the heart. Trophozoites of M. rhodei were observed in only a few eases and occurred in enlarged renal corpuscles in which the capillary tuft was atrophied and compressed. The pathology of M. rhodei was significant due to the enlargement of glomeruli from four to seven times their normal size and with an estimated increase in volume of 54 to 78 times. In addition to the functional damage to the glomeruli, there was also damage of the surrounding interstitial tissue and tubules as a result of the pressure from these enlarged glomeruli. The two myxobolid species were considered to be mainly specific to the kidney with no serious pathology in this organ, but caused significant pathology in the muscles ( M. pseudodispar ) and gills ( M. ellipsoides ).     

Distribution and feeding of juvenile fish on invertebrates in littoral reed (Phragmites) stands

Abstract – Complex interactions between fish predators and their prey have been found in structurally complex habitats built by submerged macrophytes. In contrast, the role of comparably structured littoral reed stands in shaping biotic interactions has not been investigated. We hypothesised that reed stands may be a valuable feeding habitat for juvenile fish, and that perch and roach may segregate along the spatial and dietary niche dimensions between reed and open water habitats. In contrast, the protection effect of reed against predators was assumed to be rather low because of the lower plant volume infested in reed when compared with submerged macrophytes. We analysed biomass and growth of juvenile (age 0 and age 1) perch and roach in littoral reed habitats and in open water habitats in front of the reed in the shallow Lake Müggelsee over 4 months in 2000. Sampling was conducted by point-abundance electrofishing over the full diel cycle (day, dusk, night, dawn). Zooplankton and benthos biomasses were determined in both habitats as well, and habitat-specific diet of fish was assessed during day and night. Roach were more frequent than perch in both habitats. Food of roach included a higher proportion of zooplankton, whereas perch fed more on macroinvertebrates. Overall, diet overlap between the fish groups was high. Diel distribution of fish did not follow the expectations of habitat segregation between perch and roach. Instead, the function of reed as refuge habitat against littoral piscivores (mainly birds) may have caused the strong daytime preference for reed in almost all fish groups, which was partly upset by roach at night. The higher behavioural plasticity of roach may explain their good performance even under the conditions of high structural complexity.