The thermal rudd Scardinius racovitzai is a Pannonian biogeographical relict species whose taxonomic status has been disputed; it was historically restricted to the thermal Peţea Lake near Oradea, Romania (Kottelat & Freyhof, 2007, Handbook of European Freshwater Fish). In the early 2010s, overexploitation of the thermal springs feeding the lake caused severe water loss, leading to near-complete desiccation in 2013–2014. Endemic fauna, including the thermal rudd, was saved in emergency rescue operations by the Ţării Crişurilor Museum (Oradea, Romania). Rescued fish were successfully bred in captivity in 2014, with offspring reintroduced to the original habitat and distributed to zoos and aquaria (Müller et al., 2018, Egyptian Journal of Aquatic Research, 44, 245–249). The negative impacts affecting the lake continued, leading to the complete destruction of the habitat in 2022. As a result, the species is now categorized as Extinct in the Wild on the IUCN Red List (Ford, 2024, IUCN Red List). In 2024, a renewed international collaboration was launched to advance ex situ conservation of the species.

During this project, breeding trials of the thermal rudd were carried out at four locations: Schönbrunn Zoo (Vienna, Austria), Țării Crișurilor Museum, Tropicarium and Oceanarium (Budapest, Hungary) and Hungarian University of Agriculture and Life Sciences (Gödöllő, Hungary). In these trials, two artificial propagations, in Oradea and Gödöllő were successful. On 7 April 2025, spawning was hormonally induced at the Țării Crișurilor Museum, resulting in fertilized egg batches. After several attempts, the Hungarian broodstock was also propagated at the end of April 2025. The 130 juveniles from the breeding trial in Oradea were introduced to Schönbrunn Zoo and Țării Crișurilor Museum, and the 85 offspring from the Hungarian broodstock were used to restock the Tropicarium and Oceanarium. The sperm bank for S. racovitzai in Gödöllő, established in 2014, was supplemented with newly preserved sperm samples from Schönbrunn Zoo. Currently, no suitable wild habitat is available for reintroduction of the rescued population, and the species can only be preserved through ex situ conservation, maintained within zoological institutions and research facilities.

We thank the Mohamed bin Zayed Species Conservation Fund (grant number: 242533675) for their funding and support.