23The organization of fish assemblages in offshore, deep channel habitats is poorly known in 24 very large rivers compared with shoreline, littoral areas. We report on the parameters and 25 testing of an electrified benthic frame trawl (EBFT), developed for monitoring the distribution Zingel streber in the river, which proved to be extremely rare in SE catches. The EBFT 35 caught larger/older individuals of many species than SE, and indicated diverse size/age 36 structure for many species offshore. Our survey revealed that offshore areas are intensively 37 used by a variety of species, which occur relatively evenly, but with variable abundance in the 38 Danube River. We suggest that even a relatively small (i.e. 2 m wide 1 m high) EBFT can be
In Europe 37% of freshwater fish are threatened. However, conservation activity is less widespread for fish compared to other vertebrate groups. The Vulnerable European mudminnow Umbra krameri is a marshland fish endemic to the Carpathian Basin. Its range and population have declined significantly since the 1990s. The main threats to the species are habitat loss and the invasive Chinese sleeper Perccottus glenii. During 2008–2012 a species conservation programme was established to rescue broodstocks from threatened populations, breed them under controlled conditions, translocate both rescued fish and their laboratory-reared offspring to surrogate habitats, and finally reintroduce offspring to their original habitats. Broodstocks from three threatened habitats were bred in the laboratory and produced offspring appropriate for stocking. Six artificial ponds were created in the pilot study area according to the environmental needs of the species, four of which proved to be suitable surrogate habitats in which translocated fish survived and reproduced successfully. Populations in the original habitats were supplemented with fish from laboratory breeding and from the natural recruitment of surrogate habitats, with special care of the corresponding broodstocks. Future challenges include improving our knowledge about the ecological processes in which the European mudminnow participates, identifying the most threatened populations, habitats suitable for restoration and potential areas for creation of surrogate habitats, and enhancing induced propagation methodology.
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