Dear colleagues, My co-authors and I are pleased to share our recent open-access publication on a rare cetacean–sirenian interaction in the Brazilian Amazon. This case report documents an agonistic interaction from tucuxi dolphins (Sotalia fluviatilis) towards an Amazonian manatee calf (Trichechus inunguis), which ultimately resulted in the death of the manatee. Case Report: Agonistic interaction between Amazonian manatee (Trichechus inunguis) and Tucuxi dolphins (Sotalia fluviatilis) in Brazil. Albuquerque L, Lucchini K, Soares ML, Kantek DLZ, Attademo FLN, Bezerra B, Luna FO (2026) Frontiers in Ethology 5:1717951. https://doi.org/10.3389/fetho.2026.1717951 Abstract: Interspecific interactions play an important role in shaping ecological relationships, yet descriptions of social interspecific interactions in aquatic mammals remain scarce. Here, we describe a rare agonistic interspecific interaction between Tucuxi dolphins (Sotalia fluviatilis) and an Amazonian manatee calf (Trichechus inunguis) in Brazil, which resulted in the death of the manatee. Such records are unique and contribute to the understanding of behavioral repertoires of aquatic mammals. On April 12th, 2004, an Amazonian manatee calf was rescued by local fishermen in Macapá, Amapá State, Brazil, after being attacked by Tucuxi dolphins. The calf was transferred to a rehabilitation center, but its condition deteriorated. On April 22nd, the animal died, and necropsy revealed external cone-shaped marks consistent with dolphin bites, internal thoraco-abdominal trauma, intestinal rupture, and pulmonary edema. Histopathological analyses indicated neurogenic shock as the cause of death. This is the first documented case of aggression of Tucuxi dolphins towards an Amazonian manatee. The record highlights the importance of monitoring interspecific interactions in overlapping habitats and contributes to the scarce literature on cetacean-sirenian interactions. The paper is freely available via https://doi.org/10.3389/fetho.2026.1717951. Kind regards, Karen Lucchini MSc and PhD student in Animal Biology/Animal Behaviour - LECC/PPGBA Federal University of Pernambuco - UFPE Biologist and Researcher GEFMar Fellow - Centro Nacional de Pesquisa e Conservação de Mamíferos Aquáticos (ICMBio/CMA) http://lattes.cnpq.br/0466847532755310 https://www.linkedin.com/in/karen-lucchini-041371174/