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Mitigation measures for downstream migratory Atlantic salmon smolts (Salmo salar L.) at migration barriers usually turn out to be insufficient to enable safe and quick passage, probably due to a lack of knowledge about their behavioural responses. Combining manual 2D tracking with hydrodynamic modelling has been rarely performed but might be useful to highlight environmental factors influencing smolt behavioural tactics and the choice of a migration route. We investigated the smolt downstream migration at a hydropower plant that offers five migration routes, including a Kaplan turbine and a fish-friendly Archimedes screw. Four behavioural tactics were defined to describe the smolt expressed behaviour, which was mainly complex and hesitant. The majority of the smolts approached more than one migration route before crossing the site and the Kaplan turbine turned out to be the most approached route, contrary to the Archimedes screw. Hydrodynamic modelling highlighted that flow velocity and water depth were used as hydraulic cues in the selection of a migration route, as the smolts preferred higher flow velocities and water depths. The comprehension of the factors influencing the research behaviour at hydropower plants may be useful to design attractive mitigation measures and to guide the smolts efficiently towards safe routes. [ABSTRACT FROM AUTHOR]

Biological invasions are a major component of global change worldwide. But paradoxically, an invasive species might also have threatened populations within its native range. Designing efficient management policies is needed to prevent and mitigate range expansions of invasive alien species (IAS) in non-native areas, while protecting them within their native range. Characterizing genetic variation patterns for IAS populations and deciphering the links between their native and introduced populations is helpful to (i) assess the genetic state of both native and non-native populations, (ii) reveal potential invasion pathways, (iii) define IAS management strategies in invaded areas, and (iv) identify native populations requiring conservation measures. The European catfish (Silurus glanis) is the largest European predatory fish. Introduced since the seventies from Eastern to Western Europe, it has colonized many waterbodies. Yet, little is known about the genetic status of non-native populations and the invasion pathways used by the species. Besides, some native populations are threatened, requiring conservation actions. Here, we describe current patterns of genetic variability of native and non-native S. glanis populations across Europe. Using microsatellite markers, we first assessed genetic variation within and between native and non-native populations. Second, we performed genetic clustering analyses to determine the genetic structure of multiple catfish populations across Europe and highlight their potential links. We revealed that native populations are more genetically diverse than non-native populations, and highlight complex introduction pathways involving several independent sources of introduction, which likely explain the invasion success of this large predatory fish across western Europe. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We studied downstream migration behaviour of Atlantic salmon smolt at a hydropower station that offers four safe (weir, new incision gate on weir, downstream bypass and Archimedes screw) and one potentially unsafe (Kaplan turbines) migration routes. We followed hatchery smolts using radio (n = 17) and RFID (n = 200) telemetry. They were released 1.2 km upstream of the hydropower station in spring 2018, in four groups, at different water discharge (18 to 37.2 m3s−1) and temperature (12.2–17.6°C) conditions. For radio-tagged smolts, the repartition of the migration routes was 41.2% for the bypass, 17.6% for both the Kaplan turbine and the weir, 11.8% for the Archimedes screw, 0% for the new incision and 11.8% of unknown route. For the RFID-tagged smolts, the repartition was 38.0% for the bypass, 56.5% for the weir or the Kaplan, 4.5% for the new incision and 1.0% for the Archimedes Screw. The median time to cross the hydropower station was 58 min, and 88.2% of the smolts succeed to continue their downstream migration. The results demonstrate a diversity of choices of migration routes and underline the importance to optimise the position of fish-friendly turbines and fish passes at hydropower stations to increase their attractiveness. [ABSTRACT FROM AUTHOR]

In laboratory fish research, the zebrafish Danio rerio (Cyprinidae) represents the equivalent of the mouse in mammalian research. This species has become a major model for studies in developmental and behavioural genetics, neurophysiology, biomedicine, ecotoxicology, and behavioural and evolutionary ecology. To meet the need for accurate and reproducible data in both fundamental and applied sciences, it is of primary importance to be able to tag and/or recognize individual zebrafish. However, classic methods used in fish ecology and aquaculture are generally difficult to apply to such small fish. Recently, various new tagging methods have been developed. This paper presents a first review of current identification and marking methods applied to zebrafish, from external observation methods (such as skin pattern recognition, fin clipping, scale regeneration, colour and transgenic methods) to the most advanced technological developments in electronic (low- and high- radio-frequencies PIT tags, microchip) and image analysis methods (video tracking). This review aims to help researchers and zebrafish facility managers select the identification method (ID) best adapted to their needs. The main characteristics of each ID method are examined (including detection range, durability, speed and repetitiveness, ID code combination, size dependence and ethical considerations), and their pros and cons are summarized in a decision table to help select the most appropriate option for a research or management program. Finally, contextual applications of these ID methods and future developments are discussed. [ABSTRACT FROM AUTHOR]

The extreme body sizes of megafishes associated with their high commercial values and recreational interests have made them highly threatened in their native range worldwide by human-induced impacts such as overexploitation. Meanwhile, some megafishes have been introduced outside of their native range. A notable example is the European catfish (Silurus glanis), one of the few siluriforms native to Eastern Europe. It is among the 20 largest freshwater fish worldwide, attaining a total length over 2.7 m and a documented mass of 130 kg. Its distinct phylogeny and extreme size imply many features that are rare among other European fish, including novel behaviours (massive aggregations, beaching), consumption of large bodied prey, fast growth rates, long lifespan, high fecundity, nest guarding and large egg sizes. The spread of the species is likely to continue due to illegal introductions, primarily for recreational angling, coupled with natural range extension associated with climate change. Here, the most recent knowledge on the current distribution and the ecology of the species are reviewed. A series of key research questions are identified that should stimulate new research on this intriguing, yet largely unknown, species and, more generally, on the ecology of freshwater invaders. [ABSTRACT FROM AUTHOR]

The dynamics of upstream movements of the yellow eel Anguilla anguilla were investigated at Lixhe on the Belgian River Meuse in an inland fish pass regularly monitored from 1992 to 2014. Based on a constant year-to-year sampling effort, we examined the abundance of ascending yellow eels and their body size, seasonal movement, and the associated water temperature and flow. Over the last 23 years, the number of ascending yellow eels has declined at an average 4.2 % per year since 1992. The abundance of eels in 2014 is estimated at 4.5 % of the ascending stock in 1992. We observed that some annual variations in eel abundance at Lixhe might be related to opening fish passes downstream of the study site. The results clearly demonstrated that long-term declining abundance of eels has resulted in increased sizes (mean increase, 4.1 mm per year since 1992) and temperatures triggering the upstream movement process (1.03 °C per decade), with earlier dates for the last eel passages reducing the difference between temperature extremes of eel passages through the fish pass during the migration season. Eel movements occurred in spring and summer at low river discharge and were mainly triggered by high-temperature events. Eels have become larger with time because of improved feeding opportunities and more growth habitats available resulting from the long-term reduction in recruitment. This study highlights the importance of investigating long time spans for a better comprehension of the changes observed in yellow eels and for the optimization of management measures and future research. [ABSTRACT FROM AUTHOR]

This study aims to investigate the upstream movement patterns of potamodromous fish species using multi-annual monitoring of modern multi-species fish passes in two medium-sized Belgian rivers: the Berwinne and the Amblève. During a 6-year monitoring period including a frequency of 1-5 times per week, the captured individuals were identified, measured and weighed to determine species abundance, and the periodicity of their seasonal movement patterns was investigated in relation to environmental factors. In the Amblève, 22 different fish species were monitored ( n = 1513 individuals; biomass of 154 kg) and 14 species in the Berwinne ( n = 3720; 408 kg). In both fish passes, inter-annual differences were observed, but the first year of monitoring was the best in terms of biomass, indicating the existence of an opening effect just after the fish passes opening, which allowed new migration routes. Salmonids and rheophilic cyprinids were predominant in terms of biomass, while minnow and spirlin were predominant in terms of number of fishes. The diversity in size ranged from 46 to 760 mm demonstrating the importance of movements in various life stages. The capture periodicity showed different mobility patterns between the adult and juvenile stages in most species. Movements occurred frequently during the circum-reproduction period for some species, but many species moved also apart from spawning period. This study highlights the omnipresence of patrimonial holobiotic potamodromous fish at different life stages that reflect their biological needs to move throughout the annual cycle. They must be considered as target species in river continuity restoration programmes and fish-pass design. [ABSTRACT FROM AUTHOR]

The movements and habitat use of resident yellow eels were studied in a stream stretch having both natural and minimum flow zones. N = 12 individuals (total length 505-802 mm) were surgically tagged with radio transmitters and released at their capture sites. They were located using manual radio receivers during the daytime from 2 to 5 days/week over periods ranging from 200 to 329 days, for a total of 1,098 positions. Eels showed home ranges ranging from 33 to 341 m (median value, 62 m), displayed strong fidelity to sites and demonstrated a great degree of plasticity in habitat use. Eels were slightly mobile throughout the year, but their movements were season and temperature dependent, with a maximum during the spring (mean water temperature, 12 °C) and a minimum in winter (3 °C). Stones and roots (utilization rate greater than 50 % of eels for more than 30 % of location days) were significantly the most frequently used habitats. Between the two flow zones, the natural flow was the most occupied, with a significantly higher proportion of resident eels (66.7 % of radio-tagged yellow eels) and longer occupation (81 % of location days) than the minimum flow zone with less suitable habitats. [ABSTRACT FROM AUTHOR]

The gonadosomatic index at spawning, absolute fecundity, and egg size for the female sexual products as well as the density and consistency of semen for the male sexual products were examined in cultured Abramis brama × Blicca bjoerkna F1 hybrids and compared with the parental species at their first sexual maturity. Females ovulated under environmental conditions, and their eggs were weighed, counted and measured. Semen of males was macroscopically examined and spermatozoa counted using a hemocytometer. Results revealed that hybridization affected the quality of female and male gametes but with an overlap between hybrids and parents. The gonadosomatic index and fecundity were significantly lower than those of parental species. Egg sizes in hybrids showed a parental effect but to the benefit of hybrids. Semen of hybrids was more diluted which was classified into two groups: the white semen overlapping slightly with parents and the aqueous without any overlap with parents. Overlapped areas between hybrids and parents in term of quality of sexual products could translate that females and males of these hybrids have the biological capacity to produce high quality gametes and thus, a greater chance to produce F2 and backcross generations in rivers. [ABSTRACT FROM AUTHOR]

From February 2006 to June 2007, we followed the movement patterns of the Rhine sculpin ( Cottus rhenanus) by combining short-term radio-telemetry ( n = 10 radio-tagged sculpin with a miniature 0.5-g transmitter) and long-term individual (PIT-tag) mark-recapture ( n = 452 PIT-tagged sculpin during six removal electric fishing operations) studies in a small tributary of the River Meuse, Belgium. During a 25- to 27-day period, the radio-tracked sculpin displayed various mobility patterns, showing frequent movement from one day to another and longitudinal home ranges from 7 to 46 m, with cumulative distances up to 149 m. During the mark-recapture study, most (99%) recaptured PIT-tagged individuals moved from their original 5-m long site, subsequently using longitudinal home ranges between 5 and 435 m (mean, 50 m; median, 20 m). The most common movement behaviour was alternation between upstream and downstream movements (62%), followed by directional upstream (26%) and directional downstream (11%) movement. Using the latest available techniques, this study builds on the current knowledge on the Cottus genus and closes gaps in the comprehension of sculpin movement and home range at a scale that had not been investigated to date. [ABSTRACT FROM AUTHOR]

A hydroelectric power plant (HPP) started operation in December 2002 on the River Lhomme, (mean annual flow: 1.78 m3 s−1; mean annual water temperature: 9.9°C). The new HPP bypasses the river over a length of 1.2 km. The minimum flow allowed in the bypassed section is currently fixed at 0.220 m3 s−1. Before the construction of the HPP, two contrasted 150-m-long reaches of the Lhomme were selected to estimate their total fish population abundance and to analyse their fish population dynamics. Electrofishing was carried out in each of these two reaches on 23 April 2002 in a natural flow situation to remove the fish. Other inventories were carried out in late April or early May in 2003, 2004, 2005 and 2006 in minimum flow conditions. The results revealed a prompt and severe decrease in the total fish biomass (up to 81% for grayling from 2002 to 2006) combined with severe changes in the fish community structure that were not observed in a reference site. The effects of the flow reduction varied considerably depending on the size of the individuals, the species concerned and their habitat availability, which was modelled using a classical physical habitat simulation (EVHA method). [ABSTRACT FROM AUTHOR]

Hybridization success at early developmental stages and larval resistance to osmotic, thermal and fasting tests in roach Rutilus rutilus, silver bream Blicca bjoerkna, common bream Abramis brama and their F1 hybrids were investigated. Results revealed that hybrid survival rates were similar to parents. At the eyed embryo stage, however, a maternal effect was observed as a general trend during hatchling and larval stages. After these stages, hybrids displayed a higher survival rate than their parents. Under stress tests, no survival was observed after 40 min for osmotic and thermal shocks and after 24 days for the prolonged fasting test in these species and their F1 hybrids. The median survivals of hybrids were intermediate between the two parents. For total mortality, hybrids were also affected by a maternal effect but to the advantage of the hybrids. [ABSTRACT FROM AUTHOR]

Adult roach Rutilus rutilus (L.) ( N = 24; 19.9–36.1 cm FL) from three highly fragmented Belgian rivers were tagged with surgically implanted radio transmitters. Their seasonal movements were observed from March to August 2004 (circum reproduction period) in river stretches delimited by two physical barriers. In the three rivers, roach displayed similar patterns of movements which were mainly influenced by the date of observation (movements increased in late April–May) and water temperature (travel distances were more important when water temperature ranged between 10°C and 14°C). Roach sometimes cleared physical obstacles. The mean distances travelled in each river were relatively short (max. 2.5 km) and mainly influenced by the length of the study reach, which was delimited by physical barriers. [ABSTRACT FROM AUTHOR]