The pikeperch (Sander luciopercaL.) possesses great potential for diversifying European aquaculture. However, studies on the genetic risk of stocking natural waters with farmed individuals of this species have been limited. Even the effect of pond culture on the genetic composition of stocks with natural-origin has not yet been determined. Our study aimed to compare the genetic variability of a wild living pikeperch population, a pond cultured broodstock (originating from the wild population) and its offspring generation. We also aimed to detect the potential signs of selection using three different methods. By analyzing the molecular data with 14 microsatellite markers, we illustrated that the impact of pond culture on the genetic diversity of fish stocks is similar to hatchery rearing due to its diversity reducing effect caused by using lower effective population sizes. Although the heterozygosity was similar in all populations (H_o= 0.68–0.71), the average number of alleles and allelic richness were significantly lower in the pond cultured stocks (NA = 7.5 and 6; AR = 7.5 and 5.9) compared to the wild population (NA = 11.00, AR = 10.47). Despite the semi-natural conditions of the present study, we detected changing selection pressure in one of the 14 microsatellite markers.

Bigheaded carps (bighead carp, Hypophthalmichthys molitrix, and silver carp, Hypophthalmichthys nobilis) and their hybrids play an important ecological and economic role in their original habitat, while their introduced stocks may pose serious ecological risks. To address questions about the persistence and invasiveness of these fish, we need to better understand their population structures. The genetic structures of bigheaded carp populations inhabiting Lake Balaton and the Tisza River were examined with ten microsatellite markers and a mitochondrial DNA marker (COI). The Lake Balaton stock showed higher genetic diversity compared with the Tisza River stock. Based on hierarchical clustering, the Tisza population was characterized only by only silver carps, while the Balaton stock included hybrid and silver carp individuals. All COI haplotypes originated from the Yangtze River. Based on the high genomic and mitochondrial diversity, along with the significant deviation from H–W equilibrium and the lack of evidence of bottleneck effect, it can be assumed that bigheaded carps do not reproduce in Lake Balaton. The present stock in Balaton may have originated from repeated introductions and escapes from the surrounding fishponds. The Tisza stock consists solely of silver carp individuals. This stock appears to have significant reproductive potential and may become invasive if environmental factors change due to climate change.

Tench is a cyprinid fish that has undergone human-induced translocations. The natural populations of the species are on the decline due to habitat loss and spawning grounds degradation. The genetic diversity of seven natural populations was investigated to establish the genetic knowledge base for successful conservation efforts and for selective breeding. Twelve microsatellite markers, the sequencing of a 615 bp section of mtDNA (Cytb) and PCR-RFLP analysis of two nuclear markers (Act) and (RpS7) were used to analyze the genetic variation and structure among 175 individuals. All microsatellite loci were found to have moderate levels of polymorphism. The pairwise Fst values between population pairings were moderate; the populations were aligned to four clusters. The Cytb gene showed 20 haplotypes; 67.1% of individuals were categorized as Eastern, while 32.9% to the Western haplogroup. Analysis of the Act and RpS7 genes showed that the level of hybridization among the two haplogroups is high within the sampled populations. Hungarian Tench populations are genetically less diverse compared to natural populations in Western-Europe, but they still represent valuable genetic resources and Lake Fertő, Lake Kolon and Csörnöc-Herpenyő populations can be optimal candidates for future selective breeding programs.

As an alternative method for preserving female genetic material, the cryopreservation and orthotopic transplantation of day-old gonadal tissue have become well-developed techniques in a few poultry species. The aim of the present study was to apply these methods for the first time to domestic geese. Cryopreservation was accomplished using the previously developed vitrification technique. Native and frozen/thawed White Hungarian geese ovarian tissue was transplanted onto Grey Landes geese recipients. Both donors and recipients were less than 24 h old. The surgical protocol previously used in chickens needed to be modified regarding anaesthesia; ketamine, xylazine, and midazolam were administered partly intramuscularly and partly intravenously. After sexual maturation, the Grey Landes recipients were paired with White Hungarian ganders, and eggs were collected and hatched individually. The origin of the offspring was determined by phenotype- and microsatellite markers. Donor-derived offspring were obtained from native and frozen/thawed ovarian tissue transplantation, which had not been published earlier. The ratio of donor-derived progeny producing layers was 40% and 58% in native and frozen/thawed gonadal tissue transplantation, respectively. The highest rate of donor-originated progeny was 78.9%. Consequently, gonadal tissue transplantation appears to be a suitable method for preserving female genetic material in domestic geese; the technique is already implemented in Hungarian gene bank practice.

The European mudminnow ( Umbra krameri Walbaum, 1792) is a relict wetland fish endemic to the Danube Basin, with Hungary representing the core of its historical distribution. We compiled published faunistic records, grey literature and standardised field-survey data from 1975–2025 to quantify long-term distribution changes across 12 Hungarian geographic regions and 200 documented localities. Confirmed persistent populations occur at 45.5% of historical localities (91 sites), including 17 “large” and 74 “small” populations. An additional 15 sites (7.5%) show only occasional recent records, whereas the European mudminnow has disappeared from 44% of its historically known localities. Most extant populations remain small and spatially fragmented. The Danube–Tisza Interfluve historically contained the highest number of localities (n = 57) and exhibited the greatest absolute loss (33 disappeared sites), primarily associated with hydrological degradation. In contrast, the Fertő–Hanság–Szigetköz Region currently represents the most important north-western refuge (21 persistent populations, including three large populations), whereas the Zámoly Basin is regionally extinct. Across all localities, invasion by the Amur sleeper ( Perccottus glenii Dybowski, 1877) (35% of sites) and documented desiccation (30.5%) were the two most frequently recorded threat categories. GLM applied to sites with known status (n = 194) showed substantially lower predicted persistence probabilities at sites affected by desiccation. At the national scale, desiccation emerged as the only clear independent predictor of reduced persistence, whereas the effects of other pressures appeared regionally heterogeneous and context-dependent. Surviving populations increasingly occur in artificial canal systems, indicating a marked shift from natural floodplain habitats towards secondary refugia. Integrated hydrological restoration, invasive-species control and genetically informed conservation management, including eDNA-based monitoring, are urgently required to prevent further contraction of this approximately 60-million-year-old Danubian endemic lineage.

The crucian carp (Carassius carassius Linnaeus, 1758) is a declining native European cyprinid, inhabiting small water bodies, primariliy threatened by climate change, anthropogenic impacts and invasive relative the Prussian carp. Despite conservation efforts across Europe, data on Carphatian Basin populations remain scarce. This study analyzed nine natural populations (257 individuals) in Hungary using thirteen microsatellite markers and mitochondrial DNA COI sequencing (187 individuals). Sequencing of mitochondrial DNA revealed a presumably introduced Baltic stock in addition to the Danube lineage and the presence of Prussian carp hybrids in part of the populations. Microsatellite markers also confirmed the latter, but there were populations in the southern region free of hybrids. Genetic diversity was found to be moderate (Ho: 0.49–0.61; Ar: 6.01–7.98). Depending on the genetic structure analysis method, two or three main units with low to moderate differentiation were detected (FST: 0.054–0.192). Based on gene flow, the Danube-Drava region showed a separation from the northern areas and the populations on the eastern bank of the Danube. Eight of the nine populations examined, especially the south Danube populations, could provide a good basis for the establishment of a genetically controlled gene bank of remaining crucian carp stocks, without hybrids.