This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/jfb.14576 Patagonian grouper Acanthistius patachonicus (Jenyns, 1840) forms massive spawning aggregations in the Southwest Atlantic Alejo J. Irigoyen 1* , Cecilia Riestra 2 , Sofía Lopez 2,3 and Ana M. Parma 1 1 Centro para el Estudio de Sistemas Marinos (CESIMAR), Consejo Nacional de Investigaciones Científicas y Técnicas (CCT CENPAT–CONICET). Puerto Madryn U9120ACD, Argentina. 2 Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Mar del Plata B7600EEP, Argentina. 3 Instituto de Investigaciones Marinas y Costeras (IIMyC), Consejo Nacional de Investigaciones Científicas y Técnicas (FCEyN, UNMDP-CONICET), Cc1260, 7600 Mar del Plata, Argentina. E-mail: alejo@cenpat-conicet.gob.ar Phone: (+54) (2965) 451024 Fax: (+54) (2965) 451024 Funding information: Field work was supported by PADI Foundation. AJI, PDA and AMP were supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) of Argentina. This article is protected by copyright. All rights reserved. Running head: Spawning aggregation of a reef fish