Search Results (7)

The use of mesocosms in stream ecology has long attracted the attention of researchers due to the clear advantages these systems offer for manipulative experiments. Despite some limitations, they provide an effective way to create semi-natural conditions in which selected parameters can be artificially controlled. This study presents the ALPSTREAM eco-hydraulic laboratory, a mesocosm system designed to mimic the conditions of an alpine stream (Ostana, NW Italy). The structure of this system is unique and consists of six 25-m-long flumes, fed directly by the Po River and equipped to regulate key hydraulic parameters. The paper describes the structure of this system and presents two case studies to illustrate some potential applications. The first aimed to analyze the impact of different aquatic insects (scrapers) on periphyton dynamics. The second tested the feasibility of the flumes for the ex situ breeding of a threatened fish species, the European bullhead (Cottus gobio L.). The purpose of this paper is to raise awareness of this facility and make it available to researchers interested in eco-hydraulic studies in mountain environments. Full article

Niche partitioning studies are essential to understand the mechanisms that allow ecologically similar species to coexist. The Rhone streber (Zingel asper) and the European bullhead (Cottus gobio) are both benthic riverine fishes that consume macroinvertebrates. Both species are protected under European legislature. We focused on trophic niche partitioning between these species, as sufficient access to trophic resources is an important requirement for long-term coexistence. We used a combination of faeces metabarcoding dietary data and prey community data to evaluate dietary overlap, trophic niche variation and dietary preferences. Sampling was performed in three sites along the Durance River (France). Both species consumed a wide range of macroinvertebrates but neither C. gobio nor Z. asper selected the most abundant taxa (chironomids and simuliids). Both species selected larger mayfly (Baetis and Ecdyonurus) and caddisfly (Hydropsyche) taxa. Dietary overlap was generally high but declined when large mayflies were rare. Contrasting secondary prey preferences and trophic niche variation may allow these species to exploit the same preferred mayflies in periods of abundance and to avoid competition during resource scarcity. We propose that dietary partitioning may support the coexistence of these two ecologically similar, benthic predators. Full article

The round goby is an invasive fish in Europe and North America that threatens native species by predation and competition. Its habitat preferences are similar to those of the European bullhead, which it displaces from shelters and out-competes for available resources. We assessed the microhabitat preferences, shelter use, and activity of the round goby and European bullhead in single-species experiments in habitat simulator systems to investigate their behavior in a novel environment. Fish were video-recorded for 28 h in the presence of shelter and feed with water velocity ranging from 0.00 to 0.96 m s⁻¹. The two species showed similar behavior under given conditions. A primary difference was in stress-induced behavior in the initial phases of observation. The round goby spent more time in movement when outside the shelter and a longer time in the escape zone in the exploration period during light. Our results confirmed a significant preference of round goby for low velocity areas and a preference for higher velocities in the European bullhead. Both species were able to cope with velocities > 0.7 m s⁻¹. Therefore, the reported invasion success of round goby is probably not driven by space use or activity patterns, but rather by higher adaptability. Full article

Fish passes facilitate fish movement in fragmented river systems, yet they can also provide important habitat functions. This study investigated the fish community composition of different constructed habitat types (fluvial habitats, floodplain ponds) within fish passes in relation to habitat characteristics in order to deduce recommendations for fish-friendly designs of such structures. Fish community structures within passes differed significantly from those in the main river, comprising a high number of rheophilic species in fluvial habitats (Thymallus thymallus, Hucho hucho, Salmo trutta, Cottus gobio, Chondrostoma nasus, and Barbus barbus), and of stagnophilic species in floodplain ponds (Rhodeus amarus, Scardinius erythrophthalmus, Misgurnus bipartitus, and Tinca tinca). During summer, floodplain ponds also provided important juvenile habitats for the target species C. nasus and B. barbus. Differences between the two habitat types in fish abundance were mostly explained by differences in macrophyte coverage, gravel, boulders, temperature, and current speed. The findings of this study stress the important habitat functions of fish passes. They also suggest that integration of diverse habitat structures, especially of currently hardly considered constructed floodplain ponds into fish passes, can greatly enhance their fish communities and contribute to the restoration of several declining target species of conservation. Full article

The hypothesis that liver lipid accumulation in fish is an adaptive strategy to survive the winter in the high-altitude environment was assessed in this study. During summer 2019, specimens of Cottus gobio were sampled in 15 watercourses of Friuli Venezia-Giulia Region (Italy) to verify if hepatic steatosis is or not normally present in the species. To do this, hepatic vacuolization was assessed by histology using a semiquantitative score. Furthermore, C. gobio were also captured during the ice-free season at Dimon Lake (1872 m a.s.l.) and But Stream (520 m a.s.l.) to compare the trend in lipid accumulation: water temperature, hepatosomatic index (HSI), gonadosomatic index (GSI), Fulton’s condition factor (K), and lipid area percentage (lipid %) were measured monthly. Findings revealed that liver steatosis is rather common in C. gobio. However, the trend in lipid accumulation of this species differed between Dimon Lake and But Stream. Based on the HSI and the GSI, the reproductive cycles differed in fish from the two environments (April–May in But Stream; May–June in Dimon Lake). While K values remained unchanged in the But Stream specimens, significant changes were recorded for Dimon specimens. The increase in lipid % from July to August in the Dimon Lake specimens coincided with greater food availability. With the rapid drop in lake water temperature in October, the lipid % decreased due to slower metabolic rate and lipid utilization from liver stores. There was a slight decrease in lipid % in the But Stream specimens, indicating that lipids were not being accumulated. Introduced years ago, the Dimon Lake bullhead population has since adapted to the winter conditions at high elevation. Full article

The aim of this study was to describe liver alterations observed in a bullhead (Cottus gobio) population from a high-mountain lake (Dimon Lake; 1857 m a.s.l.) located in Carnic Alps (Northeast Italy). Two fish sampling campaigns (summer and autumn) were performed in 2017 to explore the possible causes of this phenomenon. In addition, to investigate the typical liver features of C. gobio, control specimens were captured from Degano Creek in the same seasons. Total length, weight, and liver weight were recorded in fish from both sampling sites. In addition, Fulton’s condition factor (K) and hepatosomatic index (HSI) were calculated. Stomach contents were also analyzed. Liver from each specimen was sampled, and histological examination was carried out. Liver steatosis (L) (nuclear displacement and cytoplasm vacuolization) were histologically evaluated by assigning a semiquantitative severity score. A significant difference in L was found between Dimon Lake and Degano Creek in both summer (Mann–Whitney test; p = 0.0001) and autumn (Mann–Whitney test; p < 0.0001). Regarding HSI, a significant difference was also recorded between Dimon Lake and Degano Creek in summer (Mann–Whitney test; p < 0.0001) and also in autumn (Mann–Whitney test; p < 0.0001), but no seasonal change in K values was recorded between the two sites in both summer (Mann–Whitney test; p = 0.8589) and autumn (Mann–Whitney test; p = 0.6415). A significant positive correlation between HSI and L was found (ρS 0.573). The causes of this abnormality might be related to adaptation by the fish to the high-altitude environment, accumulating lipids in the liver to tackle the adverse season, which lasts for 6 months of the year. Nonetheless, our study does not preclude steatosis induced by a nearly exclusive chironomids diet in bullhead from Dimon Lake. Full article

Application of instream habitat models such as the Mesohabitat Simulation Model (MesoHABSIM) is becoming increasingly popular. Such models can predict alteration to a river physical habitat caused by hydropower operation or river training. They are a tool for water management planning, especially in terms of requirements of the Water Framework Directive. Therefore, model verification studies, which investigate the accuracy and reliability of the results generated, are essential. An electrofishing survey was conducted in September 2014 on the Stura di Demonte River located in north-western Italy. One hundred and sixteen bullhead—Cottus gobio L.—were captured in 80 pre-exposed area electrofishing (PAE) grids. Observations of bullhead distribution in various habitats were used to validate MesoHABSIM model predictions created with inductive and deductive habitat suitability indices. The inductive statistical models used electrofishing data obtained from multiple mountainous streams, analyzed with logistic regression. The deductive approach was based on conditional habitat suitability criteria (CHSC) derived from expert knowledge and information gathered from the literature about species behaviour and habitat use. The results of model comparison and validation show that although the inductive models are more precise and reflect site- and species-specific characteristics, the CHSC model provides quite similar results. We propose to use inductive models for detailed planning of measures that could potentially impair riverine ecosystems at a local scale, since the CHSC model provides general information about habitat suitability and use of such models is advised in pre-development or generic scale studies. However, the CHSC model can be further calibrated with localized electrofishing data at a lower cost than development of an inductive model. Full article