At first glance, muddy, low-oxygen waters seem unattractive. For some highly specialized fish species, however, they are vital refuges. It is precisely these habitats that are increasingly threatened in Europe.
A new special issue in the journal Nature Conservation, recently published and edited by an expert group led by Josef Wanzenböck, is dedicated to these unique fish and their importance for wetland conservation.
The special issue “Biology and conservation of wetland fishes in Europe” brings together selected papers from the international conference “The Fish of Muddy Waters,” which took place in Vienna in October 2025. The focus was on fish species adapted to the specific conditions of wetlands and their surrounding areas.
Fish fauna monitoring in Illés Pond VI in the Szada Pilot Area. Photo by Sándor Tatár. From Bajomi et al., 2026
These include, among others, the European mud minnow (Umbra krameri), the weatherfish (Misgurnus fossilis), and the crucian carp (Carassius carassius). At the same time, non-native fish species that have since become established in the peripheral areas of floodplains and other wetland habitats were also examined, and their impact on ecosystems was discussed.
What makes these fish special is their ability to cope with conditions under which many other species could not survive. In small, muddy bodies of water, oxygen levels can be very low at times. The fish species found there are adapted to these extreme conditions and can therefore provide important insights into the state of their habitat. This means that fish inhabiting wetlands are much more than just rare species. They can serve as indicators of the ecological health of their habitats. If these specialized fish are struggling, this often points to changes or a deterioration in the entire ecosystem.
For instance, a study by Sallai et al., covers 50 years of records from Hungary, the core of the European mud minnow’s range, found that the species has disappeared from 44% of its historically known localities. Its lineage is roughly 60 million years old, yet surviving populations are increasingly confined to artificial canals. In the research article, drying wetlands emerged as the clearest threat.
The issue also offers cause for hope. Bajomi and col. showed that in two small, isolated artificial ponds, mud minnows released by conservation teams were still breeding 7 to 10 years later, which shows that carefully designed translocations can create safe refuges for the European mudminnow (Umbra krameri).
For more research like this, access the full Special Issue here: https://natureconservation.pensoft.net/issue/5260/
This was precisely the focus of the conference “The Fish of Muddy Waters.” The goal was to strengthen the link between research and conservation and to draw attention to fish species that often receive less public attention than larger or economically more significant species. The exchange between international scientists and representatives of nature conservation organizations should help to consolidate existing knowledge and develop new approaches to the protection of endangered wetland fish.
Fish have always held a firm place in our culture and are closely linked to the use of water bodies. However, the little-known inhabitants of wetlands reveal another side of this relationship: they highlight just how closely the conservation of individual species is tied to the protection of their habitats. Research on these species can thus also help raise awareness of the importance of wetlands and lay the groundwork for more effective biodiversity conservation.
This newly published special issue offers insight into current research on these specialized fish species and makes selected results of the Vienna conference accessible to an international audience of experts.
Cover image credit to: Lukas Fuxjaeger