Squalius Cephalus Research Articles

Effects of pharmaceutically active compounds (PhACs) on fish body and scale shape in natural waters.

BackgroundIn recent years, there are growing concerns about pharmaceutically active compounds (PhACs) in natural ecosystems. These compounds have been found in natural waters and in fish tissues worldwide. Regarding their growing distribution and abundance, it is becoming clear that traditionally used risk assessment methodologies and ecotoxicological studies have limitations in several respects. In our study a new, combined approach of environmental impact assesment of PhACs has been used.MethodsIn this study, the constant watercourses of the suburban region of the Hungarian capital (Budapest) were sampled, and the body shape and scale shape of three fish species (roach Rutilus rutilus, chub Squalius cephalus, gibel carp Carassius gibelio) found in these waters were analyzed, based on landmark-based geometric morphometric methods. Possible connections were made between the differences in body shape and scale shape, and abiotic environmental variables (local- and landscape-scale) and measured PhACs.ResultsSignificant connections were found between shape and PhACs concentrations in several cases. Despite the relatively large number of compounds (54) detected, citalopram, propranolol, codeine and trimetazidine significantly affected only fish body and scale shape, based on their concentrations. These four PhACs were shown to be high (citalopram), medium (propranolol and codeine), and low (trimetazidine) risk levels during the environmental risk assessment, which were based on Risk Quotient calculation. Furthermore, seven PhACs (diclofenac, Estrone (E1), tramadol, caffeine 17α-Ethinylestradiol (EE2), 17α-Estradiol (aE2), Estriol (E3)) were also categorized with a high risk level. However, our morphological studies indicated that only citalopram was found to affect fish phenotype amongst the PhACs posing high risk. Therefore, our results revealed that the output of (traditional) environmental/ecological risk assessment based on ecotoxicological data of different aquatic organisms not necessarily show consistency with a “real-life” situation; furthermore, the morphological investigations may also be a good sub-lethal endpoint in ecotoxicological assessments.

Traces of tramadol in water impact behaviour in a native European fish

Tramadol is a widely used analgesic with additional antidepressant and anxiolytic effects. This compound has been reported in continental waters reaching concentrations of µg/L as a consequence of its inefficient removal in sewage treatment plants and increasing use over time. In this study, European chubs (Squalius cephalus) were exposed to 1 µg/L of tramadol in water for 42 days with a subsequent 14 days of depuration. Our results revealed that chubs exposed to this analgesic underwent changes in their behaviour as compared to the control group. The behavioural outcome was also influenced by the individual concentration of tramadol in brain tissue. In particular, experimental fish presented anxiolytic-like effects, characterized by less bold and less social individuals. Exposed animals were less frequently out of the shelter and moved a shorter distance, indicating that they explored the new environment less during the boldness test. In the novel object recognition experiment, although they distinguished the new item, they examined it less and displayed a reduced activity. Shoal cohesion was disrupted as observed in an increased distance between individuals. After the depuration phase, this alteration remained whereas the boldness effect disappeared. Moreover, the degree of behavioural changes was correlated with the concentration of the substance in brain. According to our findings, chronic presence of tramadol in the environment can impact the fitness of exposed aquatic fauna by altering evolutionary crucial behaviours.

The fishes of the Bolaman Stream, Northern Turkey

In this study, the fish species inhabiting the Bolaman Stream drains to the Black Sea from the Fatsa coast (Ordu Province, Turkey) was reported for the first time. The study was caught out non-periodically by sampling from seven stations in the Bolaman Stream between July 2017 and November 2018. Fish samples were captured with an electroshock device. With this study, it was determined that the fish fauna of the Bolaman Stream is represented by 10 species in five families (Acheilognothidae, Cyprinidae, Gobiidae, Leuciscidae, and Salmonidae). These species were as follows, respectively Rhodeus amarus, Barbus tauricus, Capoeta banarescui, Neogobius fluviatilis, Ponticola turani, Alburnus derjugini, Squalius cephalus, Vimba vimba, Alburnoides fasciatus, and Salmo coruhensis.

Fish from urban rivers and with high pollutant levels have shorter telomeres.

Environmental pressures, such as urbanization and exposure to pollutants may jeopardize survival of free-living animals. Yet, much remains to be known about physiological and ecological responses to currently-released pollutants, especially in wild vertebrate ectotherms. We tested the effect of urbanization and pollution (phthalates, organochlorine and pyrethroid pesticides, polychlorobiphenyls, polybromodiphenylethers, polycyclic aromatic hydrocarbons, and some of their metabolites) on telomere length, a suggested biomarker of life expectancy, in the European chub, Squalius cephalus, from urban and agricultural rivers of the Marne hydrographic network, France. We showed that telomere length was reduced in chub from urban rivers. Moreover, among the wide range of anthropogenic contaminants investigated, high levels of phthalate metabolites in liver were associated with shorter telomeres. This study suggests that urbanization and chemical pollution may compromise survival of wild fish, by accelerating telomere attrition.

Trophic consequences of competitive interactions in freshwater fish: Density dependent effects and impacts of inter‐specific versus intra‐specific competition

Abstract Determining the comparative impacts of increased intra‐ versus inter‐specific competition is important in freshwater ecosystems for understanding the ecological changes that can result from activities such as fish stocking events (using alien and/or native fish species), as well as from natural processes that elevate population abundances (e.g. increased annual recruitment success). While increased inter‐specific competition can result in slower growth rates and/or reduced population density in the weaker or less abundant competitor, it is important that this is assessed in relation to the impacts of increased intra‐specific competition. We tested how the strength of inter‐specific competition from a co‐existing species varies with abundance, and how this compares with increased intra‐specific competition. Fish were the model taxa, as their growth rates strongly correlate with competitive success. Replicated pond mesocosms (150 days) used chub Squalius cephalus in an allopatric control (n = 5; C5) and allopatric treatment (n = 10; C10), and in sympatric treatments (n = 5) with European barbel Barbus barbus (n = 5 (T1), 10 (T2) and 15 (T3)). Treatment effects were tested on fish‐specific growth rates (SGRs), and the size and position of the trophic and isotopic niche (stomach contents and stable isotope [SI] analyses respectively). Chub SGRs were significantly higher in C5 versus all other treatments, but did not differ among the other allopatric and sympatric treatments. Chub trophic niche sizes in T1 to T3 were significantly smaller than C5, indicating more specialised diets in the presence of barbel. Chub trophic niche size in C10 was, however, larger than C5 and T1, indicating a shift to a more generalised diet as intra‐specific competition increased. As SGRs reduced in treatments, so did the predicted extent of fish SI turnover, with SI data in T1 to T3 not at isotopic equilibrium with their diet in the mesocosms at the experiment's end. Following conversion of fish SI data to represent values at 95% isotopic turnover, chub isotopic niches also revealed shifts to a more general diet as intra‐specific competition increased, but to more specialised diets as inter‐specific competition increased. Increased intra‐ and inter‐specific competition impacts on the trophic and isotopic niches were contrasting; both metrics indicated niche constrictions in sympatry but niche expansions in allopatry. Impacts on fish growth were evident from both. These results emphasise that the trophic consequences of competition in freshwater fish can differ between stocking events involving the release of conspecifics or other species, with this having important considerations for how freshwater fish communities are managed for angling exploitation.

Performance of cyprinids in non-reversing mirrors versus regular mirrors in tests of aggressiveness

Mirror tests have been used to test aggressiveness because they reduce the variability of the real opponent and allows for repeated measurements. Regular mirrors have also several disadvantages due to the inability to display a head-to-tail position during lateralization. Recently, a method using a non-reversing mirror was developed, which eliminated this disadvantage, but was tested in a single species only. The present study reflects the need for validating the non-reversing mirror test in other species, represented by chub (Squalius cephalus L.) in the present study, due to species-specific manifestations of aggressiveness. The prediction that a non-reversing mirror would lead to more aggressive interactions than a regular mirror in chub was confirmed. The durations of aggressive interactions were longer in fish exposed to the regular mirror test with specific significance in case of the frontal and the lateral displays. The individuals maintained the same level of aggressiveness throughout both tests, suggesting that both tests are valid for testing the aggressiveness. Nevertheless, due to higher number of interactions performed, a non-reversing mirror may offer a stronger stimulus and could represent a real contest better than the regular mirror. Therefore, the non-reversing mirror test should be recommended for use in future studies.

Making up the bed: Gravel cleaning as a contribution to nase (Chondrostoma nasus L.) spawning and recruitment success

Abstract Spawning substrate quality is a major factor influencing the early ontogeny of European nase (Chondrostoma nasus), a target species of conservation. Analogous to findings from salmonids, restoration of spawning grounds was hypothesized to enhance spawning, development and thus recruitment success of nase, by improving the substrate quality, and subsequently spawning site use, egg infiltration and protection of larvae in the interstitial zones before emergence. These assumptions were tested using a comparative approach by cleaning 50% of the area of each spawning ground in two Bavarian rivers. Substrate cleaning resulted in an immediate reduction of ~70% fine sediment content with improvements still detectable 2 months later. Spawning nase used the restored areas of spawning grounds preferentially, which was evident in the number of spawning fish and the significantly higher number of eggs laid. Infiltration of eggs into the interstitial zone was distinctly more successful in the opened interstices of the cleaned spawning substrate, where they were found down to a depth of 20 cm. The same was true for larvae, which could be found down to 30 cm and up to 13 days after hatching. Moreover, higher peaks in the drift density of emerging larvae from the restored spawning substrate were detected (2.5 compared with 1.7 larvae m−3 discharge for the River Mangfall and 0.3 compared with 0.03 larvae m−3 for the River Sims). These results clearly indicate that gravel cleaning is a successful short‐term restoration tool for nase spawning grounds. It is a quick, cheap and effective method for the conservation management of nase, which may also be applicable to other riverine species with a similiar ecology and incubation time, such as Barbus barbus, Squalius cephalus, Leuciscus leuciscus and Phoxinus phoxinus. This especially holds true if streams lack internal dynamics and suffer from high loads of fine sediment and colmation.

Can top-down effects of cypriniform fish be used to mitigate eutrophication effects in medium-sized European rivers?

Eutrophication seriously threatens the ecological quality and biodiversity of running waters. In nutrient-enriched streams and shallow rivers, eutrophication leads to excessive periphyton growth and, in turn, biological clogging, oxygen depletion in the hyporheic zone and finally a reduction in the hyporheic habitat quality. Top-down control of the food-web by manipulating fish stocks, similar to the biomanipulation successfully applied in lakes, offers a promising approach to mitigating the effects of eutrophication in shallow rivers, especially those in which major reductions in nutrient input are not feasible. We conducted a reach-scale experiment over 4 years in a medium-sized eutrophic river to assess whether the top-down effects of two important large European cypriniform fish species, herbivorous common nase (Chondrostoma nasus) and omnivorous European chub (Squalius cephalus), would mitigate the effects of eutrophication. The enhancement of fish stocks was expected to reduce biological clogging, via the top-down control of periphyton by benthic grazing and enhanced bioturbation, thus increasing oxygen availability in the hyporheic zone as well as water exchange between the surface water and the hyporheic zone. As expected, enhancing the stocks of nase and chub increased both oxygen availability and vertical exchange flux of water in the upper layer of the hyporheic zone. However, periphyton biomass (chlorophyll a) was significantly reduced only in deeper pool habitat. Thus, while experimental biomanipulation in a shallow river significantly mitigated the effects of eutrophication in the hyporheic zone, top-down effects on periphyton biomass were rather small. Overall, to our knowledge, our results provide first evidence that the biomanipulation achieved by enhancing herbivorous and omnivorous fish stocks has the potential to mitigate the effects of eutrophication in medium-sized European rivers.

Spatial and Temporal Trends in Contamination of the Czech Part of the Elbe River by Mercury Between 1991 and 2016.

We summarized available data concerning contamination of the Czech part of the Elbe River by mercury and assessed the potential risks to humans connected with the consumption of contaminated fish. Total mercury concentrations were evaluated in dorsal muscle of chub (Squalius cephalus) and bream (Abramis brama) that were collected at 11 sampling sites in the period from 1991 to 2016. Significant differences among sites were found for both species. The highest contamination was observed near the non-ferrous Kovohute metal works at Celakovice and also downstream from the Spolana chemical plant at Neratovice. A significant decline in contamination with time (concentrations decreasing from 1.65 to 0.22mgkg-1; p = 0.004) was revealed in chub downstream from the Spolana plant. Calculated hazard indices (HIs) were below 1, therefore, adverse health effects on the general Czech population connected with the consumption of fish from the Elbe River were not expected.

The impact of a catastrophic flood on species and size composition of the diet of fish-eating birds

Floods in June 2013 affected significant portions of the Czech Republic (total damages amounted ~600 millions of euro). This study examines the impact of catastrophic flood on the species composition and size of fish prey in the diet of the common kingfisher (Alcedo atthis), a fish-eating bird, nesting and hunting on Botič stream (Prague, Czech Republic) in 2013. Hundred and forty years water (flow 74.5 m3 s−1) caused considerable damage to property and it is likely that the character and size composition of biota, especially fish, changed. This should be reflected naturally in the diet of resident kingfishers. The diet of kingfishers before and after the flood were investigated from the mass of regurgitated pellets, which were collected from the nest tunnel and chamber immediately after the successful breeding period before and after the flood event. Before the flood (normal situation; flow 0.4–1.5 m3 s−1), the average length of fish caught was 6.5 cm LT (total length), average weight 2.6 g, and the index of food diversity was 1.58. After the flood, the average length of fish caught was 7.5 cm LT, weight 4.1 g, and the index of the food diversity was 1.36. It was evident that after the flood kingfishers were forced to hunt significantly larger prey. Six fish species (Gobio gobio, Squalius cephalus, Perca fluviatilis, Scardinius erythrophthalmus, Rutilus rutilus, Pseudorasbora parva) which were hunted both before and after the flood composed 96.5 and 99.8% of the catch (by numbers). Surprisingly, the impact of floods may not always be reflected in the species composition of the diet of fish-eating birds, it mostly depends on the presence of fish broadly occurring in the stream, natural stability of the fish stock and on the composition of the fish assemblage in the upstream catchment area.

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.

Organosomatic indices and leukocyte formula of chub (Squalius cephalus L) from the Suturlija River

Coefficients of organs, along with haematological characteristics, represent an important means of monitoring the health and condition of fish. Organosomatic indices show the state of organ systems and individual organs. They manifest as changes in size, which are reflected through a decrease or increase, under the influence of environmental factors. Chub individuals from the Suturlija River were used for analysis. The paper analyses the Fulton's condition factor, heart, liver, and spleen coefficients as a condition factor. Furthermore, the values ​​of total length, standard length, and body weight were determined for all individuals. Also, certain haematological parameters were analysed in the paper: total leukocyte count and differential blood count. A total of 19 chubs caught from the Suturlija River were analysed. The obtained result of Fulton's condition factor (1.53) indicates favourable habitats for chub individuals in the Suturlija River. The results of organosomatic indices are without major variations between individuals (CSI = 0.184, SSI = 0.992, HSI = 0.133). The mean leukocyte count was 45.857x109/l, with the highest proportion of lymphocytes in the differential blood count.

Environmentally relevant levels of four psychoactive compounds vary in their effects on freshwater fish condition: a brain concentration evidence approach.

BackgroundThe aquatic environment has been contaminated with various anthropogenic pollutants, including psychoactive compounds that may alter the physiology and behavior of free-living organisms. The present study focused on the condition and related mortality of the juvenile chub (Squalius cephalus). The aim of the study was to test whether the adverse effects of the antidepressants sertraline and citalopram, the analgesic tramadol and the illicit drug methamphetamine, on fish condition exist under environmentally relevant concentrations and whether these effects persist after a depuration period. Innovative analyses of the fish brain concentrations of these compounds were performed with the aim to show relationship between compound brain tissue concentration and fish condition.MethodsThe laboratory experiment consisted of 42 days of exposure and a subsequent 14-day depuration period with regular monitoring of the condition and mortality of exposed and control fish. Identical methodology, including individual brain concentration analyses for the tested compounds, was applied for all substances. Additional study on feeding under sertraline exposure was also conducted. The feeding was measured from the 28th day of the exposure, three times in a week, by observation of food intake during 15 minutes in social environment.ResultsThe effects of particular psychoactive compounds on chub condition varied. While sertraline induced a lower condition and increased mortality, the effects of methamphetamine were inverse, and tramadol and citalopram had no significant effect at all. Individual brain concentrations of the tested compounds showed that the effects of sertraline and methamphetamine on fish condition were increased with brain concentration increases. Additionally, the food intake was reduced in case of sertraline. In contrast, there was no relationship between tramadol and citalopram brain tissue concentration and fish condition, suggesting that the concentration-dependent effect is strongly compound-specific. Methamphetamine was the only compound with a persistent effect after the depuration period. Our results demonstrate the suitability of the brain concentration evidence approach and suggest that changes in fish condition and other related parameters can be expected in freshwater ecosystems polluted with specific psychoactive compounds.

Evaluation of the performance of successive multispecies improved fishways to reconnect a rehabilitated river

The equipping of barriers with fishways has useful applications for testing hypotheses of fish migration and connectivity in river networks, but multiple passage performance for potamodromous fish is poorly known to date. The aim of this study was to analyse the performance of new fishways installed in the river Vesdre (Belgium). Thirty-eight barbel (Barbus barbus; mean: 508 mm, 2133 g) and seven chub (Squalius cephalus; mean: 372 mm, 935 g) were captured by electric fishing and fish pass monitoring and were equipped by RFID-tags and/or radio-transmitters. They were translocated downstream of three different fishways (nature-like pool-type, block ramp, and technical pool-type) in the lower course of the Vesdre. Detection antennas connected to automatic receivers were placed downstream and upstream of each fishway to evaluate the approaching rate, the overall and adjusted passage efficiencies, the passage delays, temperature, dates and time period. The best passage performance and passage delays were observed for the block ramp fishway (88%; 9 h median time to pass) in comparison with pool structures (47 and 73%; 94 and 144 h median time to pass, respectively). The overall passage efficiency was 18.2 and 29.4% for two successive fishways, and 18.2% for three fishways. Passages occurred mainly during dark periods at median temperatures of 14 °C (barbel) and 12.3 °C (chub), and during highly variable flow conditions. This study provided evidence of the success rate of the reestablishment of the ecological continuity in the river Vesdre as a result of the construction of improved fish-passage structures.

Test-dependent expression of behavioral syndromes: A study of aggressiveness, activity, and stress of chub.

Aggressiveness has been one of the behavioral traits most examined with various standard testing methods. We used two distinct methods (the mirror and the real opponent tests) to evaluate individual aggression and relate it to the activity and individual stress of chub (Squalius cephalus L.). Three hypotheses were formulated and tested: (a) there is a significant positive relationship between the aggressiveness of individuals measured with the mirror and the real opponent tests, indicating their convergent validity; (b) the irregularities in response to the aggressiveness and activity tests lead to the context-specific expression of the behavioral syndromes; and (c) there is a significant positive relationship between the stress induced in individuals by both tests of aggressiveness, demonstrating individually consistent stress-coping strategies. The first and the second hypothesis were confirmed, while the third hypothesis was rejected. Our results suggest that particular tests of aggressiveness could act as a situation with high strength, leaving little variation between individual responses. Thus, we propose that for the proper interpretation of various studies using different tests to study identical behavioral traits, it is important to consider the convergent validity of not only the tested behavioral traits but also the individual stress responses. The chub also showed stress relieve through aggressiveness, suggesting the species as a prospective animal model to the study interaction between the stress and the aggressiveness. A detailed aggression ethogram of chub was provided to facilitate the use of this specie in future studies.

First Occurrence of Eustrongylides spp. (Nematoda: Dioctophymatidae) in a Subalpine Lake in Northwest Italy: New Data on Distribution and Host Range.

The genus Eustrongylides includes nematodes that infect fish species and fish-eating birds inhabiting freshwater ecosystems. Nematodes belonging to the genus Eustrongylides are potentially pathogenic for humans; infection occurs after the consumption of raw or undercooked fish. In the two-year period 2019–2020, a total of 292 fish belonging to eight species were examined for the occurrence of Eustrongylides spp. from Lake San Michele, a small subalpine lake in northwest Italy. The prevalence of infestation was 18.3% in Lepomis gibbosus, 16.7% in Micropterus salmoides, and 10% in Perca fluviatilis. The other five fish species (Ameiurus melas, Ictalurus punctatus, Squalius cephalus, Carassius carassius, and Scardinius erythrophthalmus) were all negative for parasite presence. There were no significant differences in prevalence between the three fish species (Fisher’s exact test; p = 0.744). The mean intensity of infestation ranged from 1 (M. salmoides and P. fluviatilis) to 1.15 (L. gibbosus), and the mean abundance ranged from 0.1 (P. fluviatilis) to 0.28 (L. gibbosus). There were significant differences in the infestation site between the four muscle quadrants (anterior ventral, anterior dorsal, posterior ventral, and posterior dorsal) and the visceral cavity (Kruskal–Wallis test; p = 0.0008). The study findings advance our knowledge about the distribution and host range of this parasite in Italy.

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

Abstract 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. 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. 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. 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. 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.

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments.

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Spatial and Temporal Variation in Feeding Habits Squalius cephalus Living in Suat Uğurlu and Hasan Uğurlu Dam Lakes

In this study, spatial and temporal feeding habits of Squalius cephalus (L., 1758) sampled in the Suat and Hasan Uğurlu Dam Lakes and the river areas above and below the dams was investigated by stomach contents analysis. For that purpose, the sampling was performed at 4 different stations: The first station, the Dam Exit (DEX) river areas; the second, Suat Uğurlu Dam Lake (SUDL); the third, Hasan Uğurlu Dam Lake (HUDL) and the fourth, the Dam Entrance (DEN). A total of 332 individuals of Squalius cephalus were sampled during the four seasons. Empty stomach ratio was 54.41%. Accordingly, the highest number of empty stomach was observed in autumn (for 60 individuals). According to stomach contents analysis, a total of 37 different prey species belonging to 6 main groups were identified. Of the identified prey species, insects group was the most preferred feed source (39.5%), followed by Chlorophyta (12.48%), Bacillorophyta (9.93%), aquatic plants (8.04%), detritus (5.57%) and Crustaceae (1.27%), respectively. The dominant food item in spring were Bacillariopyhta (3.49 ml), Chlorophyta (4.52 ml) and insects (14.44 ml) while Chlorophyta (1.93 ml), insects (1.38 ml) and detritus (1.41 ml) in summer. It was determined that insects and aquatic plants predominated stomach of S. cephalus in autumn, whereas they mostly fed on insects and preferred plant originated Bacillariohyta group in winter. Dams caused changes in the number of fish and food sources along the river. S. cephalus fed on insects, Bacillariophyta and Chlorophyta in DEX and SUDL; detritus, insects, Bacillariophyta in HUDL and aquatic plants, Bacillariophyta in DEN. In conclusion, it was observed that S. cephalus preferred both animal and plant materials during four seasons. More S. cephalus were captured in the river areas at the outlet of the dams and the variety of food sources consumed has been characterized more in their SUDL and HUDL.

Quantitative analysis of the pigment composition of macrophage aggregates in the spleen of chub (Squalius cephalus L., 1758) from the river Crn Drim. Influence of sex and season

Quantitative analysis of the pigment composition of macrophage aggregates in the spleen of chub (Squalius cephalus L., 1758) from the river Crn Drim. Influence of sex and season