Schizocypris altidorsalis is a fish of very restricted distribution, with its populations being known only from few water reservoirs on the border of Iran and Afghanistan. Aims. The aim was to investigate the occurrence and diversity of host-specific Monogenea on this fish. Methods. In total, 400 fish were purchased from the market and examined for the presence of Monogenea. Specimens were characterised morphologically and genetically. Key results. In total, 26.5% of fish were found to be infected with Monogenea. Further morphological and molecular studies based on the sequences of the 18S, 28S and ITS2 regions suggested that they all belong to a new species, herein named as Paradiplozoon jalalii. Our results suggest that this monogenean is a highly specific parasite of Schizocypris altidorsalis. Conclusions. Monogeneans are highly specialised host-specific parasites infecting fish gill. They can adversely affect respiration and excretory functions in fish, making them more vulnerable to illness, leading to population declines. Implications. Determining effective strategies for safeguarding endangered fish can be challenging in conflict zones, such as the area studied here. Additionally, the parasite identified in our study, with its blood-feeding habits, could contribute to the extinction of its fish host, subsequently leading to its own extinction. An unanswered question lingers regarding the potential extinction of other symbionts of Schizocypris altidorsalis if the fish faces extinction.

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