Host-parasite interface of Caryophyllaeus laticeps (Eucestoda: Caryophyllidae) in three species of fish

Abstract. The host-parasite interface of Caryophyllaeus laticeps has been investigated in naturally infected bream, Abramis brama (L.), chub, Leuciscus cephalus (L.), and roach, Rutilus rutilus (L.), by light and electron microscopy. The fish were caught in the Ruhr-lake near Bochum. Bream showed the highest rate of infection and also harboured the largest worms compared to the two other host species. In all three cyprinids, the worms' scolices caused local compression of the host's intestinal epithelium. At the attachment site of scolices of medium- to large-sized worms, the intestinal epithelial cells were vacuolized and their brush border ruptured. These pathological effects were most pronounced in bream, which also showed conspicuous granulomas in the tunica propria adjacent to the scolices. A heavy infiltration of eosinophilic granulocytes was noted in chub and roach at the worms' attachment site. In bream, only the smallest worms provoked a slight eosinophilic reaction. It is concluded that the worms within the three host species were of different ages and that the chronic stage of infection, associated with the formation of granulomas, was only reached in bream, the major host.     

Insights into myxozoan composition and physiology revealed by histochemical properties of myxospores

Myxozoa (phylum Cnidaria) are a diverse group of metazoan parasites that predominately infect fish. Little is known regarding the composition and physiology of their myxospore life stage. The objective of this work was to investigate the composition of myxospores and extrasporogonic stages of nine myxozoan species infecting various teleost fish using histochemical staining techniques. Thirty histochemical stains were applied to formalin-fixed, paraffin-embedded tissues processed routinely for light microscopic evaluation. The polar capsules were the most consistent stain target across the taxa examined. Polar capsule staining with Alizarin red, von Kossa and methyl green-pyronin suggests the presence of intracapsular calcium and phosphate, which may contribute to polar filament discharge or pathogenesis of host invasion. The shell valves and suture lines of most myxozoans were stained with Luna and phosphotungstic acid haematoxylin stains, consistent with the presence of chitin and microfibrils, respectively. Vacuoles were consistently highlighted by diastase-susceptible periodic acid-Schiff and Grocott's methenamine silver staining, indicating glycogen. Other histochemical stains exhibited inconsistent staining across the taxa, suggesting differences in myxospore composition potentially reflective of physiologic variations and tissue tropisms. This work provides some information on conserved features and taxa-associated composition of myxospores and lends insight into myxozoan physiology and host–parasite interactions.     

Diet and feeding relationships of two Iberian cyprinids

The diet and feeding interactions of the Iberian roach, Rutilus alburnoides (Steindachner), and chub, Leuciscus pyrenaicus Günther, were studied in the Sorraia river system. Seasonal shifts in the diets were examined to determine trophic overlap between the two species. Dipteran larvae were the dominant item in the diet of roach with the exception of summer and early autumn when dipteran adults became important. Ephemeroptera nymphs and imagos were the two principal food categories in chub diet. Plant material and terrestrial insects were consumed by both species mostly in the summer and autumn, periods of low availability of aquatic invertebrates in temperate streams. A low dietary overlap was found, probably resulting from differences in their seasonal foraging activity, but also from a compromise between the consumption of highly abundant plant material and rare animal food items.     

Zschokkella russelli Tripathi (Myxozoa: Myxosporea) from the five-bearded rockling, Ciliata mustela L., (Teleostei: Gadidae) in Wales

Abstract. Up to 88-9% of five-bearded rocklings, Ciliata mustela L., from three localities in Wales harboured the coelozoic myxozoan parasite Zschokkella russelli Tripathi. Previously recorded only from the gall-bladder of British rocklings, Z. russelli was also found to produce proliferation, enlargement and thickening of hepatic ducts, lowering of the duct epithelium and pericholangitis. Histological, scanning and transmission electron microscopy techniques were used to examine the parasite, and comparisons were drawn between Z. russelli from Welsh fish and infections recorded elsewhere, particularly from Plymouth, Devon.     

Complete developmental cycle of Myxobolus pseudodispar (Gorbunova) (Myxosporea: Myxobolidae)

Myxobolus pseudodispar (Gorbunova) is a common parasite of the muscle of roach, Rutilus rutilus L., whereas its actinosporean development occurs in two oligochaete alternate hosts. This paper reports the complete developmental cycle of this parasite in the oligochaete alternate host Tubifex tubifex and the roach. In laboratory experiments, parasite-free T. tubifex specimens were infected by myxospores of M. pseudodispar collected from roach in Lake Balaton. Parasite-free roach fingerlings were infected with floating triactinospores (TAMs) released from oligochaetes on day 69 after challenge. Young plasmodia and spores in roach were first recorded on day 80 post-exposure (p.e.). Myxospores collected from experimentally infected roach initiated a new development in T. tubifex and the resulting TAMs infected roach. No infection of roach resulted from feeding oligochaetes containing mature triactinospores.     

Movement of fish between a river and its backwater: diel activity and relation to environmental gradients

Abstract –  Movements of fish, in particular roach Rutilus rutilus , perch Perca fluviatilis, rudd Scardinius erythrophthalmus, bleak Alburnus alburnus and chub Leuciscus cephalus (age ≥ 1+) in relation to environmental variables were examined between the River Morava, Czech Republic, and a rehabilitated former meander. Data were taken over seven 24-h periods in April–June 1997 using two back-to-back traps. Of 170 fish captured, 70% moved from the backwater to the river. Diel activity differed between sampling dates, but overall bleak, roach and chub moved mainly between dusk and dawn, whereas perch moved throughout most of the day. Rudd showed bi-modal (mid-day, midnight) activity. However, avoidance behaviour could have biased results for species known to be wary of traps. Water level changes, temperature and illumination were among the main environmental factors influencing fish movement, along with spawning migrations relevant for most species. In all specimens, over 65% individuals captured were ready to spawn. Most of them, except for perch, were moving out of the backwater towards the river.     

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.     

Swimming ability and differential use of velocity patches by 0+ cyprinids

Abstract– The ability of chub, dace and roach to resist displacement in a laboratory channel was not only controlled by species-specific swimming ability, but also by the fishes'ability to locate areas of reduced velocity. Dace were better able to withstand high velocities than roach. Chub were better at locating slow flowing patches than either roach or dace throughout their early development. Only chub larvae shifted towards slower flowing patches as velocity increased. All juveniles shifted to slower flowing patches at high velocities.     

Histopathology, immunohistochemistry and ultrastructure of the intestine of Leuciscus cephalus (L.) naturally infected with Pomphorhynchus laevis (Acanthocephala)

The histopathology, immunohistochemistry and ultrastructure of the alimentary canal of chub, Leuciscus cephalus (L.), from the River Brenta, naturally infected with the acanthocephalan Pomphorhynchus laevis Müller, 1776, was studied and described. Of 62 chub examined, 54 (87%) were infected with P. laevis ; the intensity of infection ranged from five to 130 parasites per host, and a density of 8 P. laevis per cm² was common. Examination of histological material of infected chub revealed that both male and female acanthocephalans deeply penetrated all layers of the gut wall by means of their slender neck, bulb and proboscis. As a result, a capsule was formed around the bulb and proboscis on the external surface of the host intestine. In parasitized chub, four main types of reaction against the body of the acanthocephalan were recognized. Pomphorhynchus laevis caused local damage to the intestinal wall, eliciting catarrhal-erosive enteritis in the lumen and a fibroblastic-collagenous and fibro-epithelioid encapsulation in its thickness with tissue zonation according to the depth of parasite penetration. Furthermore, eosinophilic granular cells (EGC) within the inflammatory tissue were identified by immunohistochemical methods and transmission electron microscopy.     

Pentacapsula neurophila sp.n. (Multivalvulida) from the central nervous system of striped trumpeter,Latris lineata (Forster)

Striped trumpeter, Latris lineata, are being experimentally cultured by the Tasmanian Aquaculture and Fisheries Institute at Taroona, Tasmania. Fish surviving over 30 days post-hatching have frequently developed nervous aberrations associated with a severe granulomatous meningoencephalomyelitis. The myxozoan parasite Pentacapsula neurophila sp.n. was revealed as the parasite causing the disease in the striped trumpeter juveniles. Measurements made of isolated spores indicated that the organism was distinct from all previously described Pentacapsula species. This is the first report of a marine myxozoan parasite of the genus Pentacapsula in Australian waters.     

The influence of parasitism on fish population success

Abstract The influence of parasitism on first‐year growth and recruitment success of two cyprinid species in the Yorkshire Ouse catchment, England, was investigated using a 14‐year dataset. This study demonstrated a significant role of parasitism in growth and recruitment success of roach, Rutilus rutilus (L.), and European chub, Squalius cephalus (L.) populations. Muscle infections by Bucephalus polymorphus Baer (Digenea), Myxobolus pseudodispar Gorbunova (Myxozoa) and Myxobolus pfeifferi Thélohan were considered important, with significant relationships between these parasites and year‐class strength and age‐0 fish length. Other parasites, such as Phyllodistomum sp. and Goussia sp., were implicated in host success to a lesser extent. Parasitism may be a major factor in recruitment and account for a high proportion of the variation in year‐class strength, although this varied among locations.     

A comparative study of the myxosporeans Myxidium rhodei Léger, 1905 and Myxidium pfeifferi Auerbach, 1908 in roach, Rutilus rutilus L.

Abstract. The morphology and dimensions of Myxidium rhodei and M. pfeifferi were studied in roach originating from two different geographic locations (Greece and UK) using both scanning and light microscopy. The measurements and morphology of both mature spores and immature stages (trophozoites and spores) were studied and compared. No differences were observed in the morphology of mature or immature spores of both species when examined under light and SEM. Furthermore, no differences were found in the dimensions of the mature spores of both species in all fish. However, immature spores of both species were found to be smaller but wider than mature ones in all organs and in both habitats. Size differences between the two species were only seen in immature spores, M. rhodei immature spores being always larger than those of M. pfeifferi. When comparing the dimensions of the spores between the two habitats, these were larger and wider in the Greek fish than those in the British fish. The information in this study suggests that, in roach, M. pfeifferi is undistinguishable from M. rhodei and that similar studies should be carried out on the tench, Tinca tinca L., the type host of M. pfeifferi.     

Recruitment patterns of six species of cyprinid fishes in the lower River Trent, England

Abstract – Fisheries data were collected for six species of 0-group cyprinid fishes from eight sites in the lower reaches of the River Trent, England, between May and October 1999 inclusive, using a micromesh seine net. Recruitment and growth patterns were observed via monthly length–frequency histograms and estimations of mean length. In the cases of roach and dace, growth was approximately linear through the summer, before declining in September and October. In the cases of chub and gudgeon, and to a lesser extent bream and bleak, however, there were suggestions of multiple recruitment events. It is argued that some of the fish species examined in the present study adopt fractional or protracted spawning strategies in the lower River Trent.     

Variation in the trophic position of common stream fishes and its relationship to the presence of a rare fish,northern leatherside chub (Lepidomeda copei)

Variation in trophic position can be caused by structural changes in food webs that may affect the presence of, or be affected by the presence of, individual species. We examined variation in the trophic position of fishes across 14 stream sites in the Bear River drainage, WY, USA. This drainage is the focus of ongoing conservation of northern leatherside chub (Lepidomeda copei). Our goals were (i) to describe variation in trophic position of individual species and (ii) to determine whether these measures differed between sites with and without northern leatherside chub. Mean trophic position of individual fish species varied between 0 and 3 trophic positions across sites. For two of these species, trophic position declined at sites without northern leatherside chub. Importantly, habitat surveys from a previous study at 10 of these sites revealed no differences in habitat suitability for northern leatherside chub. This suggests that trophic position revealed systematic differences among sites that were not apparent based on traditional species‐habitat modelling. We outline possible mechanisms behind these patterns and argue that monitoring variation in trophic position can complement traditional, habitat‐based methods for understanding species distributions.     

Morphology,seasonality and phylogeny of Zschokkella soleae sp. n. (Myxozoa,Myxosporea) parasite of Solea solea (L.) (Pleuronectiformes,Soleidae) from Ghar El Melh Lagoon,Tunisia

A new Myxosporea, Zschokkella soleae sp. n., was found in the gall bladder and the bile of common sole, Solea solea (L.), from Ghar El Melh Lagoon in north‐east Tunisia. This is the first record for the presence of Zschokkella species in Tunisian waters. The parasite's plasmodia are polysporic with variable size and shape. Some plasmodia appeared attached to the gall bladder epithelium while others were found free in bile. Mature spores are ellipsoidal in frontal view 13.8 ± 0.38 μm long and 10.86 ± 0.40 μm wide with two equal size spherical polar capsules 3.6 ± 0.43 μm in size. The prevalence of infection seems to correlate with host size and changes over the year with maximum percentage in summer. Based on the 18S rDNA sequence data, Z. soleae sp. n. is readily distinguishable from other myxozoan DNA sequences in GenBank. Phylogenetically, the new species is placed in the freshwater Myxidium clade including several Zschokkella spp. infecting the gall bladder. Morphology, histology as well as DNA sequence analysis indicate that the examined species differs from all previously described Zschokkella species.     

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.     

Real-time PCR detection of Parvicapsula pseudobranchicola (Myxozoa: Myxosporea) in wild salmonids in Norway

The myxozoan genus Parvicapsula contains 14 species infecting fish, some of which are known to cause severe disease in farmed and wild salmonids. Parvicapsula pseudobranchicola infections were first reported from seawater-reared Atlantic salmon, Salmo salar, in Norway in 2002 and have since then been an increasing problem. The present study describes a Taqman real-time PCR assay for specific detection of P. pseudobranchicola. The Taqman assay targets the 18S rRNA gene of P. pseudobranchicola and is able to detect as few as ten copies of the target sequence. Using the described assay, P. pseudobranchicola was detected in both farmed and wild salmonids, indicating that wild Atlantic salmon, sea trout, Salmo trutta, and Arctic char, Salvelinus alpinus, may be natural hosts of the parasite. Parvicapsula pseudobranchicola was found in samples from wild salmonids in the far south and the far north of Norway, displaying a wide geographic range of the parasite. Farmed salmonids showed P. pseudobranchicola infection levels many folds higher than that observed for wild sea trout, indicating that farmed Atlantic salmon are subjected to an elevated infection pressure compared with wild salmonids.     

Cryptocaryon irritans (Ciliophora): primary infection in thick-lipped mullet, Chelon labrosus (Risso)

Abstract. Cryptocaryon irritans (Ciliophora), isolated from the reef fish, Grammistes sexlineatus Thumberg, was established as primary infections in mullet, Chelon labrosus (Risso). Only a small percentage (<22%) of exposed theronts established infection under controlled conditions. This is discussed in relation to the probability of host parasite contact and susceptibility. There was no evidence of density-dependent or intra-specific competition in trophont establishment, a strong linear relationship being found between the levels of exposure and infection. Infection intensity was assessed in relation to host survival, indicating a 90% probability of host death following levels of >200 trophonts per gram of host. A close temporal association between host death and trophont exit was found, possibly as a result of epidermal disruption leading to dysfunction of osmoregulatory and respiratory systems.