Water quality as a determinant of the composition of fish parasite communities

To investigate the relationship between fish parasite communities and water quality level, metazoan parasites were examined in 157 specimens of chub (Leuciscus cephalus L.), sampled in four lowland water courses (northern Italy): Ticino river (unpolluted), Naviglio Pavese Canal (slightly polluted), Lambro river near the Merone village (polluted) and near Monza (severely polluted). Dactylogyrus vistulae, Paradiplozoon ergensi, Bucephalus polymorphus, Acanthocephalus anguillae and larval stages of Tylodelphys clavata were found in all the sampled sites. The distribution of Lamproglena pulchella and Pomphorhynchus laevis was limited to the unpolluted and slightly polluted river sectors, while Asymphylodora tincae, glochidia, along with larval stages of Diplostomum spathaceum, were absent in the severely polluted site. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity), the degree of interactivity among parasites, as well as parameters of species richness and diversity suggest that the structure of parasite communities are affected by the water contamination level.     

Anglers' records as a tool for assessing changes in fish populations

Published anglers’ records from Polish rivers between 1966–1991 were used to show shifts in body weight of two obligatory riverine species: barbel [Barbus barbus(L.)], and chub [Leuciscus cephalus (L.)]. The body weight of barbel significantly decreased while that of chub did not. In 1966–89, the quality of inland waters continuously decreased, a result mainly from nutrient element input (domestic and agricultural). Hence, we consider two factors which were mainly responsible for reduction in fish size: overfishing and, perhaps, eutrophication.     

Cypriniform fish in running waters reduce hyporheic oxygen depletion in a eutrophic river

1. The hyporheic zone is an important habitat for benthic invertebrates and early-developmental stages of gravel spawning fish. However, the eutrophication of running waters and, in turn, the excessive periphyton biomass leads to its biological clogging. The result of these processes is oxygen depletion and a reduction in the habitat quality of the hyporheic zone.
2. This study assessed whether top-down effects of two important European river fish species, the large herbivorous cypriniform common nase (Chondrostoma nasus, L.) and the large omnivorous cypriniform European chub (Squalius cephalus, L.), can reduce eutrophication effects in the hyporheic zone. A 4-week mesocosm-based field experiment in a eutrophic river was conducted using cage enclosures stocked or not with either nase or chub.
3. The top-down control of periphyton was expected to reduce biological clogging and thereby increase oxygen availability in the hyporheic zone. Accordingly, we hypothesised that in enclosures stocked with either fish the concentrations of dissolved oxygen in the hyporheic zone would be higher and the periphyton biomass would be lower than in enclosures without fish stocking.
4. Hyporheic oxygen concentrations were significantly higher in enclosures stocked with either nase or chub than in enclosures without fish stocking. However, periphyton ash-free dry mass was significantly reduced only in enclosures stocked with nase, not in those stocked with chub. Thus, the positive effects of nase and chub on hyporheic oxygen availability were caused by different mechanisms.
5. Our results demonstrate that nase and chub can reduce eutrophication effects in the hyporheic zone of running waters. Hence, protecting and enhancing stocks of herbivorous and omnivorous fish will contribute to restoring the hyporheic zone in efforts to preserve biodiversity in eutrophic rivers.

     

Behavioural pattern in cyprinid fish below a weir as detected by radio telemetry

Changes in the behaviour of cyprinids belonging to different ecology groups were observed below a weir that was restricting their upstream migrations during the spawning period May–July. Positions of chub Leuciscus cephalus (L.), Prussian carp Carrasius auratus gibelio (Bloch 1783), bream Abramis brama (L.) and white bream Blicca bjoerkna (L.) were recorded every 12 min over a 24‐h period using an automatic data logger (ALS) in the upper Elbe River, Czech Republic. For all observed species, two activity peaks occurred; however, the interspecies timing of these peaks differed. Peak times for chub, bream and white bream occurred at night and during daylight, whereas Prussian carp was active mostly at night. Specimens belonging to the rheophilous group suggested more efficient behavioural tactics in passing the weir, staying below the obstacle one month longer than did eurytopic species.     

The occurrence of Caryophyllaeus laticeps in the nase Chondrostoma nasus from Austrian rivers: possible anthropogenic factors

Between April 2003 and November 2006 a total of 198 nase Chondrostoma nasus (L.) were examined for parasites from seven river sites in Austria. The selected sites showed different levels of anthropogenic alterations in river morphology ranging from pristine areas, with minor anthropogenic alterations, to strongly physically altered rivers. A variety of parasites were recovered from the skin, gills, swimbladder and eyes, with Caryophyllaeus laticeps (Pallas) being identified as the only cestode species occurring in the intestine. This is the first record of this species in nase in Austria. Caryophyllaeus laticeps was confined to the first 20% of the intestine, even in heavily infected hosts. The occurrence of C. laticeps within the fish population seems to be correlated with the degree of anthropogenic changes of the nase's habitat. In rivers with a high degree of ecological integrity or in rivers that are only partially dammed, C. laticeps is either absent in C. nasus or occurs with low prevalence (5.6-20%) and low mean intensity values (1.0-4.0). Where anthropogenic factors have changed the entire river into a reservoir, and fish cannot escape, the prevalence of infection with C. laticeps increases from 46.2 to 78.2% and the mean intensity from 8.8 to 17.2.     

Assessing the efficiency of connectivity measures with regard to the EU-Water Framework Directive in a Danube-tributary system

The effect of restoring connectivity for fish by the construction of 11 fish ladders in the Pielach and Melk rivers, both tributaries to the Danube in Austria, was monitored using electric fishing and fish traps between 1999 and 2004. In order to assess the efficiency of connectivity rehabilitation measures pre- and post-project data combining electric fishing and trap catch data were analyzed by means of three fish-based assessment methods: a MUlti-Level concept for a Fish-based, river-type-specific Assessment of ecological integrity (MULFA), the Fish Index Austria (FIA) and the European Fish Index (EFI). The effect of adding qualitative trap catch data to electric fishing data on metrics and indices was also tested and the magnitude of the effect was related to the distance of the sites from the river mouth. The results clearly demonstrated the significant contribution of connectivity rehabilitation measures to the ecological integrity of rivers like the River Pielach where morphological conditions are good, whereas remaining channelization still limits the success of connectivity measures in the River Melk. Trap catch data were found to represent an essential source of additional information to assess the efficiency of connectivity measures shortly after their implementation. The negative correlations of the magnitude of the effect of different indices and metrics with the distance of assessment sites from river mouths obviously underline the importance of the river Danube as a source for the re-colonization process. While the indices tested were found to have limited ability to reflect short-term response of fish assemblages to continuum rehabilitation, guild metrics were able to detect improvements of the ecological status shortly after the implementation of connectivity measures. Six metrics showed significant differences between pre and post-project data reflecting the expected increase of the ecological integrity: (1) Fish Region Index (FRI; FIA, MULFA), (2) number of subdominant species and (3) number of flow-guilds (FIA), (4) number of type specific species (MULFA), (5) number of benthic species and (6) number of potamodromous species (EFI); the FRI differences were only significant when trap catch data were added. The EFI indicated a decline of ecological integrity through increases in the density of omnivorous species and the relative number of tolerant species as well as a decrease in the relative number of intolerant species. Significantly decreasing responses with the distance from the river mouth were documented by the EFI and MULFA-index, the FRI (FIA, MULFA), total biomass and for the number of type specific species (MULFA). Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Growth and habitat separation in eight cohorts of three species of cyprinids in a subalpine lake

Synopsis Distribution and growth of the embryos, larvae and juveniles of Rutilus rutilus (roach), Scardinius erythrophthalmus (rudd) and Leuciscus cephalus (chub) from an oligotrophic subalpine lake in Tyrol, Austria, were studied during the first three to four months after hatching. R. rutilus was the first to spawn, a single cohort hatching around May 23rd. Four cohorts of S. erythrophthalmus hatched between June 19 and August 1. Three cohorts of L. cephalus hatched between July 3 and 25. The length/weight relationship of all species changed at a length of approximately 15–16 mm. R. rutilus, hatching at the lowest temperature, also showed the lowest growth rate during early life (maximum 10.4 per cent fresh body weight day^–1). In the other two species relative growth rates up to 20% day^–1) were measured. Rudd and chub remained in the shallow littoral during the whole period of observation, whereas roach left the littoral a few weeks after hatching and migrated into deeper water. A subtle shift in vertical distribution was observed for the first cohort of rudd which moved into slightly deeper water when the second cohort made its appearance.To whom correspondence should be addressed     

Isolation and characterization of microsatellite loci from chub Leuciscus cephalus (Pisces: Cyprinidae)

Twelve microsatellite markers were isolated from chub Leuciscus cephalus Linné, 1766 (Cyprinidae), a freshwater fish widely distributed in Europe. We assessed the level of genetic diversity for these loci in 24 individuals sampled in the Rhone river watershed. Nine loci were polymorphic, displaying from two to 13 alleles per locus with expected heterozygosity ranging from 0.160 to 0.887. Simultaneous migration of different polymerase chain reaction products was developed for routine analysis of L. cephalus populations.     

Assessment of instream structures for habitat improvement for two critically endangered fish species

The number of fish habitat improvement schemes has greatly increased in response to the widespread degradation of aquatic ecosystems. However, many of these enhancement projects often fail to create expected habitat conditions, because they are rarely planned and executed with inputs from the species’ habitat requirements throughout their life histories, and it is frequently assumed that the implementation of a specific instream structure for habitat improvement will always benefit all species present. Using a 2D hydraulic model, the present study evaluates the potential habitat improvement for two critically endangered fish species—the Southwestern arched-mouth nase Iberochondrostoma almacai and the Arade chub Squalius aradensis—resulting from simulating the introduction of different instream structures (islands, lateral bays, and deflectors) in a modified Mediterranean river reach. The introduction of islands in the river channel was found to be the best improvement measure for YOY and juvenile nase and chub, as shown by increases in the mean annual Weighted Usable Area (WUA) of more than 100 and 50%, respectively, compared to the present conditions. On the other hand, the simulation with current deflectors proved to be the worst scenario, particularly for nase, with mean annual WUA decreasing by 3.6, 17.8 and 22.7% for YOY, juveniles and adults, respectively. The findings of this study point to the need to account for different species life-history stages when modelling the implementation of instream structures for habitat improvement and also provide a sound basis for future conservation-related studies conducted in Mediterranean rivers that harbour other threatened “sister” species.     

Interactions between immunocompetence,somatic condition and parasitism in the chub Leuciscus cephalus in early spring

Relationships between immunocompetence, somatic condition, parasitism and water temperature in a wild population of chub Leuciscus cephalus were investigated. The effects of a rapid temperature increase in early spring were studied for both sexes as water temperature affects immunocompetence. Investment in gonads and activity of mucus lysozyme were negatively correlated; lysozyme activity decreased as temperature increased. No correlations were found between lysozyme activity and parasitism or intensity of infection by monogeneans, the most abundant metazoan parasite group in L. cephalus. There was a positive correlation, however, between respiratory burst intensity and parasitism. Indices of investment in gonads and spleen were correlated, showing that energetic reserves allowed either investment in gonads and spleen, or that spleen investment, even if often used in other studies in immunoecology, was not always a significant indicator of immunocompetence during this period. This last proposition is supported by the lack of correlation between spleen investment and other factors linked to immunocompetence.     

Variation in fish growth characteristics along a river course

Variation in the growth patterns of roach, Rutilus rutilus (L.), pike, Esox lucius L., and chub, Leuciscus cephalus (L.) was examined along the upper Warta River, where human impact (mostly pollution) has influenced the longitudinal zonation on the fish assemblage. Significant differences were found in the exponent of weight-length relationships for roach and chub populations occupying different zones of the river, but no such variation was observed in pike. Moreover, pike growth was isometric, whereas roach and chub grew allometrically, with regression coefficients (slope) above 3. Although the length-at-age data were similar for each zone, the von Bertalanffy parameters (L _inf, K and t ₀) suggest that there may exist some inter-zone variation in the overall growth patterns of these species. All the species grew better in the zone where the index of relative abundance (relating dominance of a particular species to its maximum abundance in river system) achieved its highest value. The results suggest that a relative abundance index expressed in this way can be a good index of habitat quality.     

Larval rearing of chub, Leuciscus cephalus (L.), using decapsulated Artemia as direct food

Little is known about the larviculture of the chub, Leuciscus cephalus (L.), an endangered cyprinid species endemic to European flowing waters. The use of decapsulated Artemia cysts as food for chub larviculture was investigated. After 3‐day feeding with the rotifer Brachionus calyciflorus, the larvae were fed on different diets: (i) dried decapsulated Artemia cysts, (ii) Artemia nauplii, (iii) rotifers for seven more days and then Daphnia collected from a pond, and (iv) an artificial diet. After a 24‐day rearing period, the highest survival rate was obtained with the larvae receiving decapsulated Artemia cysts. Feeding of the larvae with an artificial diet resulted in a significantly lower survival rate compared with the other groups. At the end of the experiment, the larvae fed on Artemia nauplii yielded a significantly higher mean length compared with the other groups. Feeding an artificial diet resulted in a significantly lower average weight and mean length gain compared with the other groups.     

Changes of nase Chondrostoma nasus L. occurrence in the Wislok River,southern Poland,after stocking with pond reared juveniles

Nase Chondrostoma nasus L., once one of the most common fish species in the upper reaches of central European rivers, is now considered endangered throughout its natural range. Since 2000 the Department of Ichthyobiology and Fisheries, Warsaw Agricultural University, has co‐operated with the Polish Anglers Association in Krosno to study the effects of river restocking with pond‐farmed nase juveniles. The experiment is carried out on Wislok River, where nase was very twenty years ago but has now completely disappeared. Selected parts of the river are stocked with tagged, one‐summer and 1 year‐old juveniles. Changes in nase occurrence, and their growth and foraging behaviour have been analysed.     

Distribution and Habitat Use of Sturgeon Chubs (Macrhybopsis Gelida) and Sick-Lefin Chubs (M. Meeki) in the Missouri and Yellowstone Rivers, North Dakota

Sampling was conducted on the Missouri and Yellowstone rivers, North Dakota to obtain information on the distribution, abundance and habitat use of the sturgeon chub (Macrhybopsis gelida) and sicklefin chub (M. meeki)(Family Cyprinidae), two declining benthic fish species native to the Missouri River basin. The study area consisted of three distinct river segments, the Missouri River near Williston, the Missouri River near Bismarck (below Garrison Dam), and the Yellowstone River near its confluence with the Missouri River. Both species of chub were collected, mainly with a benthic trawl, throughout 94% of the range sampled in the Williston and Yellowstone segments. Sicklefin and sturgeon chubs were the second and third most abundant cyprinids, respectively, collected from the Williston and Yellowstone segments. Best-fit regression models indicated that the presence of sturgeon chubs increased with decreasing depth, increasing velocity and decreasing water clarity, and that the presence of sicklefin chubs increased with increasing depth, decreasing velocity and decreasing water clarity. In contrast, no chubs of either species were collected in trawls from the Bismarck segment. This segment had significantly deeper, faster, and clearer water than both the Williston and Yellowstone segments.     

ITS rDNA sequences of Pomphorhynchus laevis (Zoega in Müller, 1776) and P. lucyi Williams & Rogers, 1984 (Acanthocephala: Palaeacanthocephala)

The internal transcribed spacers (ITS-1 and ITS-2) of the ribosomal RNA gene of Pomphorhynchus laevis (Zoega in Müller, 1776) (Acanthocephala) isolated from various fish species across Central and Southern Europe were compared with those of P. lucyi Williams & Rogers, 1984 collected from the largemouth bass Micropterus salmonoides Boulenger from the USA. The nucleotide sequences of ITS regions of P. laevis from minnows Phoxinus phoxinus (L.) and chub Leuciscus cephalus (L.) from two distant localities in the Slovak Republic were found to be 100% identical. The ITS-1 and ITS-2 of P. laevis from chub from the Czech Republic and Italy were also mutually identical, but significantly different from Slovak worms (88.7% identity for ITS-1, 91.3% identity for ITS-2). A fifth sample collected from Barbus tyberinus Bonaparte from Italy was very similar to the sympatric Italian isolate from chub, possessing four nucleotide substitutions in ITS-1 (98.4% identity). The ITS rDNA sequences of P. lucyi differed significantly from those of P. laevis; the values of identity were 51.8–56.1% for ITS-1 and 63.1–65.3% for ITS-2, and were significantly higher than the range of P. laevis within-species variability. The results based on the ITS sequences confirmed the occurrence of strains in P. laevis from Continental Europe which are well defined by molecules but reveal only slight differences in their morphology.     

Diet composition of chub,Squalius cephalus (Teleostei: Cyprinidae), in Lake Tödürge,Sivas, Turkey

Digestive tract contents of 241 specimens captured between March 1998 and November 1999 were analysed using both qualitative and quantitative methods to determine diet composition and feeding habits of Squalius cephalus (L., 1758) inhabiting Lake Tödürge, Turkey. Ages ranged from I to VI years; 60.6% of the fish were females, 39.4% males. The chub population appeared to consume a wide range of food items such as phytoplankton, zooplankton, nematodes, insects, fish, macrophytes, plant and animal detritus, whereby zooplankton (69.2%) predominated. Although individuals in the age I group preferred plankton (phytoplankton frequently; zooplankton infrequently), the older specimens (age groups IV, V and VI) behaved mostly as carnivores but also consumed some macrophytes. While there were no significant differences between diet compositions of males and females, seasonal changes were observed in frequency of occurrence, quality and quantity of consumption, and feeding activity. The chub specimens fed most heavily during spring (the pre‐spawning period: March, April and May). Highest food volume (13.0 cm³) consumed was in May and the lowest in September (2.0 cm³) while also being correlated with temperature. All of the food items were found in the digestive tract (82.1% of the specimens examined over all seasons). Highest fullness (84.9%) was reached in autumn and the lowest during summer (79.8%).     

Characterizing the trophic niches of stocked and resident cyprinid fishes: consistency in partitioning over time,space and body sizes

Hatchery‐reared fish are commonly stocked into freshwaters to enhance recreational angling. As these fishes are often of high trophic position and attain relatively large sizes, they potentially interact with functionally similar resident fishes and modify food‐web structure. Hatchery‐reared barbel Barbus barbus are frequently stocked to enhance riverine cyprinid fish communities in Europe; these fish can survive for over 20 years and exceed 8 kg. Here, their trophic consequences for resident fish communities were tested using cohabitation studies, mainly involving chub Squalius cephalus, a similarly large‐bodied, omnivorous and long‐lived species. These studies were completed over three spatial scales: pond mesocosms, two streams and three lowland rivers, and used stable isotope analysis. Experiments in mesocosms over 100 days revealed rapid formation of dietary specializations and discrete trophic niches in juvenile B. barbus and S. cephalus. This niche partitioning between the species was also apparent in the streams over 2 years. In the lowland rivers, where fish were mature individuals within established populations, this pattern was also generally apparent in fishes of much larger body sizes. Thus, the stocking of these hatchery‐reared fish only incurred minor consequences for the trophic ecology of resident fish, with strong patterns of trophic niche partitioning and diet specialization. Application of these results to decision‐making frameworks should enable managers to make objective decisions on whether cyprinid fish should be stocked into lowland rivers according to ecological risk.     

Effect of large weirs on abundance and diversity of migratory Labeobarbus species in tributaries of Lake Tana,Ethiopia

Lake Tana has a remarkable fish diversity, including 17 endemic Labeobarbus species, of which nine spawn in the inflowing rivers. Three of the migratory species are threatened, namely the endangered Labeobarbus macrophtalmus and the vulnerable L. acutirostris and L. platydorsus. In July–November 2016 during the wet season netting upstream and downstream of large weirs in two rivers and in two undammed rivers showed that weirs had a severe negative effect on migratory Labeobarbus, including the three threatened species. Of eight Labeobarbus species caught below the Gelda River weir, only L. intermedius was recorded above the weir, and in the Shini River, five Labeobarbus species were caught below the weir, but none above it. Labeobarbus diversity below the Gelda River weir (H’?=?1.4) was significantly different to that above the weir (H’?=?0), whereas in the two rivers without any weirs, Labeobarbus diversity downstream (H’?=?1.39 and 1.55) was not significantly different from that upstream (H’?=?1.52 and 1.40). Therefore, specific mitigation measures, such as fishways, need to be designed from the outset of proposed weir and instream dam construction.     

Immunocytochemical studies of the gonadotropic cells in the pituitary gland of male mullet, Mugil cephalus, during the annual reproductive cycle in both natural habitat and captivity

Using antiserum specific for the β subunit of coho salmon gonadotropic hormone II (GTH II), an immunocytochemical study of Mugil cephalus (L.) pituitaries was conducted during the annual reproductive cycle of the male in both natural habitat and captivity. The gonadotropic potency of the pituitary gland in general underwent an obvious increase during testicular development, reaching a peak at the time of reproductive maturity. During the testicular cycle of M. cephalus, the GTH cells showed an increase in immunoreactive staining intensity, granulation, hypertrophy and hyperplasia during sexual maturation. However, degranulation, vacuolization, and weakened immunoreactivity of these cells occurred during spawning. The GTH cells in the pituitary gland of M. cephalus males reared in captivity appeared with high synthetic and secretory activity but the reproductive activity declined, as reflected in the form of low values of the gonadosomatic index (GSI) and earlier resorption of the testes.     

Spawning strategies in cypriniform fishes in a lowland river invaded by non-indigenous European barbel Barbus barbus

Spawning strategies of lowland river fishes include single spawning, where reproduction generally occurs in early spring to provide 0+ fish with an extended growth season through the summer, but with a high risk of stochastic mortality events occurring, such as early summer floods. This risk can be reduced by multiple or protracted spawning strategies, where 0+ fish are produced over an extended period, often into mid-summer, but with the trade-off being a shorter growth season. The spawning strategies of cypriniform fish were explored in the River Teme, a spate river in Western England, which has non-indigenous European barbel Barbus barbus present. Sampling 0+ fish in spring and summer and across three spawning periods, B. barbus, chub Squalius cephalus and minnow Phoxinus phoxinus always revealed multiple spawning events, with 0+ fish of < 20 mm present in samples collected from June to August. Fish below 20 mm in August remained relatively small by the end of their growth season (October). For dace Leuciscus leuciscus, only single spawning events were evident, but with 0+ dace always being relatively large. Therefore, multiple spawning appears to be a common strategy that provides resilience in 0+ fish against stochastic mortality events in lowland rivers.