Throughout their history humans “tamed” not only the Danube River basin land, but also the river and its associated wetlands, drastically influencing their characteristic habitats, associations, communities, and species. One of these flagship endemic fish species in this respect is the European mudminnow (Umbra krameri Walbaum, 1792), influenced by Danube Basin geography, history, politics, and ecology. A study about this European community concern species in the context of long term human impact on its specific habitats, with potential synergic negative effects of climate change, was treated as highly needed, in an international researchers group initiative to support the efforts to provide hope for preserving this fish species and its ecosystems, and brought it back from the brink of extinction. All the characteristic inventoried wetlands which were or some of them still are natural, semi-natural, or accidental anthropogenic habitats, reveal an accentuated diminishing trend of this species areal continuity; fragmentation being the force which skewed it drastically untill now, and inducing diminishing the specific habitats quantitative and qualitative characteristics in the Danube Basin where these fish fight for survival. The main categories of human activities which impacted the climate changes in the context of this species’ habitats are: water regulation, pollution, dredging, draining, and introduction of non-native species. Overall, the diverse human impact in a climate changes in the context of this species’ habitats, Umbra krameri wetlands, creates serious perspectives on negatively influencing this at a very high scale and level. All the inventoried wetlands where Umbra krameri still survive can be considered an ecologically managed as a refuge and stepping stone wetlands, especially in the increasing climate change trend situation. Supplementary inventory studies in the field should be done for the identification of some may be unknown Umbra krameri habitats and populations.

Biotic interactions exerted by invasive species have a strong effect on ecosystems. Intraguild predation may contribute to the decline in the distribution, abundance and population size of native species and may facilitate the spread of non-native taxa. In this study, we investigated the feeding ecology of the invasive fish Amur sleeper (Perccottus glenii Dybowski, 1877) in a lowland watercourse, where it co-exists with the threatened native fish European mudminnow (Umbra krameri Walbaum, 1792). We used two sampling protocols that differed in the frequency of sampling time (e.g. monthly samplings and samplings in 10-day intervals) to provide evidence of predation, an interaction that may lead to the decline of mudminnow populations with the spread of the Amur sleeper. Aquatic macroinvertebrates comprised a major part of the diet for both sampling intervals. However, finer temporal resolution revealed the importance of fish, especially mudminnow juveniles, as a periodically available food source in the Amur sleeper’s diet. A high degree of dietary overlap was found between the different size groups of the Amur sleeper, but larger specimens tended to feed on a relatively higher proportion of fish. Our results suggested that temporal resolution of stomach content analyses may largely determine inferences on the importance of predation on juvenile mudminnow. Overall, we found that intraguild predation could contribute to the decline of European mudminnow populations, which underscores the importance of effective control measures to prevent the further spread of the invasive Amur sleeper.

The dispersal of fish into distant and isolated habitats remains a topic of continuous discussion in the field of fish biogeography. This is particularly relevant due to the perceived limitation of fish movement to what is known as active dispersal. Fish migration is often confined to interconnected water bodies, underscoring the significance of dispersal for fish inhabiting isolated aquatic habitats. However, empirical evidence for a natural (i.e. not human‐mediated) mechanism has been limited. Here we explore and provide evidence for waterbird‐mediated endozoochory as a possible dispersal mechanism in various fish species and families. We force‐fed mallards Anas plathyrynchos with fertilised eggs of nine bony fish species, covering nine taxonomic families. We recovered viable embryos of five fish taxa in the faeces of mallard, proving the ability of fish eggs to survive the passing of the digestive system of waterbirds. Moreover, the recovered eggs successfully hatched into larvae in two fish species. Taking into the flight speed and numerosity of mallards, as well as the high abundance of fish eggs, our results highlight endozoochory of fish eggs by waterbirds as a possible significant, although likely rare natural dispersal mechanism that can occur across more species than previously known in freshwater fish.

This study investigated the effects of dietary vitamin E (VE) and selenium (Se) supplementation on body weight changes, blood profile, and semen quality in Dexamethasone (DEX)-stressed Japanese quails. One hundred and five 10-week-old quail cocks were acclimated and divided into five treatment groups: negative control - G1, DEX-treated (20 mgL^-1 of drinking water) - G2, DEX + VE (180 mg kg diet^-1) - G3; DEX + Se (0.3 mg kg diet^-1) - G4; and DEX + VE (180 mg kg diet^-1) + Se (0.3 mg kg diet^-1) - G5. The birds received their respective treatments over 21 days, and various performance, hematological, and semen quality parameters were measured. Results indicated that DEX treatment significantly reduced weight gain (WG) and feed intake (P < 0.05). Supplementation with VE and Se, individually and combined, ameliorated these effects, with groups G3, G4, and G5 showing similar WG to the control. Hematological analysis revealed significant increases (P < 0.05) in packed cell volume, hemoglobin, and white blood cell count in DEX-treated groups compared to G1. Treatment did not affect blood glucose and cholesterol levels (P ≥ 0.05). Plasma antioxidant assays showed elevated superoxide dismutase and catalase functions and reduced malondialdehyde levels in G3, G4, and G5 compared to G2, indicating reduced oxidative stress. No marked differences were seen in the plasma glutathione peroxidase activities across groups. Sperm motility was impaired in the DEX-only group but improved (P < 0.05) with antioxidant supplementation. In conclusion, dietary VE and Se effectively mitigated the negative impacts of DEX-induced stress on growth, antioxidant status, and spermatozoa motility in Japanese quail cocks. VE and Se supplementation could be beneficial in enhancing the welfare and productivity of poultry under stress.

The Chinese sleeper is one of the fastest-spreading invasive fish species in Eurasia. The species’ effects on native biota are largely adverse through competition and direct predation. In this study, we systematically reviewed 240 scientific publications to synthesize current knowledge on the Chinese sleeper’s morphology, invasion history, life-history attributes, habitat use, feeding habits, parasites and genetics. Our review revealed high variability in the diet, growth, and other life-history attributes, which may largely determine the invasion success of the species. We concluded the colonization of Chinese sleeper is expected to lead to declines in native species richness and abundance, particularly in small and vulnerable aquatic habitats. These habitats frequently serve as refuges for rare and protected fish species, including the European mudminnow, whose long-term persistence is uncertain due to the continued spread of Chinese sleeper. We identified significant knowledge gaps regarding the biology and potential impacts of Chinese sleeper. We emphasize the urgent need for stricter policy regulations to prevent further introductions and manage established populations. Additionally, we highlight the importance of more intensive monitoring programs and the adoption of modern, universal detection methods—such as environmental DNA—to facilitate early detection and improve management effectiveness of the Chinese sleeper.