Michaël Ovidio

Leuciscid fishes play a crucial role in riverine ecosystems due to their high abundance, diverse life-history strategies, and specific habitat requirements. The spirlin ( Alburnoides bipunctatus ) is a rheophilic, lithophilic, and oxyphilic species, highly sensitive to pollution. Because of its strict ecological requirements, it is particularly vulnerable to anthropogenic disturbances, making it a valuable bioindicator of habitat quality in the middle to upper river zones within its distribution range. This paper aims to synthesize existing scientific knowledge on various aspects of spirlin ecology, based on an extensive review of the literature. It addresses key topics such as European distribution, morphology and identification, reproduction and life cycle, diet, movement patterns of both adults and juveniles, and habitat preferences across life stages. Furthermore, it provides an overview of human impacts on the species’ natural ecology and conservation status. A set of key research questions is proposed to stimulate further research and support the development of effective conservation strategies. This review is intended to support researchers in aquatic and fisheries sciences, river managers, and conservation practitioners.

Few studies have documented the biology, demography, and ecology of eels in deep and large riverine ecosystems, which nevertheless contain important growing areas for this endangered species. Using an original eel sampling technique, this 6-year study, started in 2018, aims to characterise the bioecology and demography parameters of eels in a deep and wide riverine ecosystem, the Meuse in Belgium. It was performed over a 125.8 km stretch and included four sampling sites. This technique, never previously used in the Meuse, trapped the eels in fyke nets when they swam back upstream, swimming against the current, after an avoidance reaction generated by the screens of hydropower facilities. Results revealed a high performance in catching eels as well as their sympatric biodiversity. The inter-site growth of eels was good. Yellow eels were mostly caught in the spring and summer under the influence of rising water temperatures, and silver eels were caught during autumn in October–December when flow and turbidity were high. A down-to-upstream decreasing demographic gradient was observed, but this pattern was not found for entry rate, catchability, survival, and immigration and emigration nets. Survival was low, and net emigration was high at a site experiencing noise pollution and hydraulic disturbance due to the work of expanding the ship lock to facilitate the passage of large boats. Effective strategies for the local eel stock and habitat management have been provided for deep and large riverine ecosystems.

Fish holes called “whédos” are excavations performed near water bodies or in the flood plains of Beninese rivers in Africa for rearing fish. During floods, they are filled and naturally colonized by various fish that remain trapped during recessions. This literature review examines fishing, aquaculture, and fish reared in traditional holes in Benin. It reports on cartography, characterization, socioeconomic aspects, challenges, and status of improvement, and proposes prospects for improving this system. Peer reviews and gray literature were used to conduct the analysis. Our review highlights 19 papers reporting on 17 whédos aquaculture experiences based on the exclusion or inclusion criteria. These results indicate that many genera can be reared in whédos, suggesting that whédos offer the possibility of going beyond the production of Clarias and Tilapia in Africa. Furthermore, the exploitation of the whédos system is fairly profitable for fishermen and their households, at approximately US$ 1713 per household annually, used to finance agricultural activities, children’s education, schooling, mitigating farmers’ vulnerability to climate risks, and health care. However, in the past two decades, there has been a significant decline in the quantity of fish collected owing to the adverse effects of hydroclimatic changes, such as floods and prolonged droughts. Moreover, water eutrophication or pollution, the risk of climate change, and fishing methods have affected crop yield over the years. The implementation of Integrated Multi-Trophic Aquaculture or Integration Agriculture-Aquaculture in whédos systems can be an effective solution for improving profitability and sustainability. The knowledge gained from this review perspective should be helpful in directing future initiatives to grow and sustain this sector of the economy and to optimize its potential to provide food for future generations.

Cyprinid fish play a major role in riverine ecosystems because of their high abundance, variety of life-history patterns, and habitat requirements. The nase (Chondrostoma nasus) is an algivorous, rheophilic, lithophilic, and oxyphilic species and is very pollution-sensitive. Thus, it represents a good indicator for habitat quality in the lower rhithral and upper potamal zones of the European river system. Due to its high level of ecological requirements, the species is very sensitive to human disturbance, leading to habitat loss and river fragmentation, climatic disruption causing a modification of hydrological and thermal regimes, organic and inorganic chemical water pollution, as well as sediment deposition. Its populations are declining in most of its distribution areas. This paper aims to synthesise the scientific knowledge on the different aspects of the nase ecology thanks to consultation of the scientific literature by addressing the following themes: European repartition, morphology and identification, reproduction and life cycle, diet, movement dynamics of adults and juveniles, and the characteristics of spawning grounds and habitats of juveniles and adults. We also provide an overview of the impact of human activities and climate shifts on natural ecology and conservation and present restoration measures based on the results of some studies that have successfully improved their habitats and/or preserved their populations. A series of key research questions are identified that should stimulate new research on this species as well as conservation measures for sustainable conservation. This paper may be particularly of interest to researchers in aquatic and fisheries sciences, river managers, and environmental conservationists.

The restoration of longitudinal connectivity in rivers allows fish to colonise new habitats. However, there is a lack of information regarding the behaviour of fish when they colonise the newly opened river stretch. We used manual radiotelemetry to tracked individuals belonging to four species (trout, nase, grayling and barbel) after their release upstream of two obstacles in the Amblève River. We observed a diversity of movement behaviours and habitats used among the studied species. All the species used potential spawning habitats with distances travelled upstream reaching 2.4 km for the grayling, 7.0 km for the barbel, 16.9 km for the nase and 18.0 km for the trout, which also use tributaries and sub‐tributaries of the Amblève River. Post‐reproduction downstream behaviours were observed in all species, but this was made difficult by the absence of downstream migration devices at dams that forced fish to seek alternative habitats. Our study suggested that allowing fish to move upstream with fishways is beneficial as the species succeeded in reaching spawning grounds, but a holistic approach combined with the installations of devices or an opening of gates to allow post‐reproduction downstream migrations would allow them to completely accomplish their biological cycle.

The efficiency of glass eel restocking as a conservation measure to restore the altered local eel stocks has never been evaluated by integrating the dimension of typological diversity of freshwater habitats in eel recruitment performance in terms of the abundance, density, growth, silvering, survival, catchability and eel yields. Here, we used the electrofishing method during a 6-year study to catch eels, and the most appropriate Jolly–Seber model was applied to estimate the demographic parameters in open populations. We found that most eels were yellow eels in the growth phase with a low abundance (eels 3⁺: 2.8% and eels 5⁺: 7.1%) of silver eels, which were only males at the MII migrating phase. Eel recruitment performance varied between sector/river habitats. Restocked eels showed annually positive allometric growth type with good length increments and better condition factors. They have survived in almost all sectors with a survival rate > 0.810. Eels were more abundant and denser (maximum 0.128 individuals m⁻²) in one sector with a high quality of habitats offering optimal living conditions in terms of the protection against predators and water flow, settlement and food availability, as revealed by it having the highest eel yields. In contrast, no eels were found in two sectors whose habitats offered a high threat of predation, poor burial properties and insufficient protection against water flow. Sector/river habitats play a key role in the success of yellow eel production and certainly, over time, future genitor production. This study provides recommendations for the management of eels and their habitats during restocking aimed at the conservation of this threatened species.