Distribution and New Fish Host for the Parasitic Isopod Livoneca redmanii Leach, 1818 (Crustacea: Cymothoidae) Collected in Northeastern Brazilian Coast

Abstract Isopods of the family Cymothoidae Leach, 1814 are frequently found as fish parasites in continental and marine environments, distributed in tropical and subtropical environments. The presence of these parasites causes histological and morphological damage to the health of their hosts, in addition to economic impacts on fishing. The isopod species Livoneca redmanii Leach 1818 occurs throughout the Atlantic Ocean, with a distribution that includes the Caribbean Sea, Brazil and, recently, the Mediterranean Sea (Egypt), parasitizing a wide range of estuarine/marine fish. In Brazil, this species is found mainly parasitizing fishes of the families Scombridae Rafinesque 1815 and Carangidae Rafinesque 1815. Thus, this study reports L. redmanii parasitizing a new host, the smallscale weakfish Cynoscion microlepidotus (Cuvier, 1830) (Sciaenidae), both collected on the coast of Maranhão, thereby expanding its list of hosts and geographic distribution in Brazil. The specimens of C. microlepidotus and their ectoparasites were collected in the municipality of Cedral (Maranhão, 02°00’34.8"S 044°30’30.3"W) by local artisanal fishermen, in June and July 2025. We analyzed 10 specimens of C. microlepidotus , containing 19 individuals of L. redmanii (4 males and 15 females) occupying the gill chambers. This report reinforces the need for studies on parasite-host interactions in coastal and estuarine ecosystems of Northeast Brazil, aiming to better understand their ecological and economic impacts. We also provide a host list for L. redmanii , showing its generalist and opportunistic nature. Furthermore, future research should investigate the dynamics of infestation in species of commercial interest.