Pseudunio marocanus (Pallary, 1918) is an endemic species of Morocco and is considered one of the world’s 100 most threatened species. The life cycle of this critically endangered freshwater mussel remains unknown. However, knowledge about the discharge period of its larvae and its ecological fish hosts is crucial to adopt more effective conservation strategies. Given this information gap, monitoring the presence of P. marocanus glochidia in fish from the Laabid River was carried out from January to May 2019 to determine the larvae discharge period. Two different approaches were used to assess the fish hosts of P. marocanus: (i) the determination of glochidia infestation rates of fishes in situ through monthly (from January to May) sampling in the Laabid River (Oum Er Rbia basin); and (ii) artificial infestation in laboratory trials using four fish species. A peak in glochidia discharge was observed at the end of February. Fully metamorphosed juveniles were detected in all native fish species, i.e. Luciobarbus ksibi (Boulenger, 1905), Carasobarbus fritschii (Günther, 1874), Luciobarbus zayanensis Doadrio, Casal-lopez and Yahyaoui, 2016, and Pterocapoeta maroccana Günther, 1874. For the first time, the glochidia discharge period and the fish hosts of P. marocanus were determined, and this information is vital to implement future conservation measures (i.e. propagation, reinforcement of populations, possible reintroductions of P. marocanus, careful management of river flow by upstream dams, and the prohibition of fishing activities during the critical glochidia discharge period). Given the increasing human pressure on freshwater habitats and biodiversity in Morocco, it is essential to preserve the native ichthyofauna to conserve this rare pearl mussel species.
