PRIMARY RESEARCH PAPER Fighting fish love robots: mate discrimination in males of a highly territorial fish by using female-mimicking robotic cues Donato Romano . Giovanni Benelli . Jiang-Shiou Hwang . Cesare Stefanini Received: 20 July 2018 / Revised: 7 January 2019 / Accepted: 25 January 2019 / Published online: 23 February 2019 Ó Springer Nature Switzerland AG 2019 Abstract Among territorial animals, several species are characterized by males showing the same initial behaviours towards both sexes, leading to significant chances of injuries against conspecifics. In this study, we investigated how visual stimuli exhibited by a female-mimicking robotic replica can be exploited by highly territorial Betta splendens males to discrimi- nate males from females. In addition, we tested the effect of light stimuli, mimicking the colour pattern of a reproductive female, on the consistence of courtship displays in B. splendens males. The intensity of male behaviours used in both courtship and not-physical agonistic interactions (e.g. fin spreading and gill flaring) was not importantly modulated by different stimuli. Conversely, behavioural displays used specif- ically in male–female interactions significantly increased when the robotic replica colour pattern mimicked a reproductive female. Furthermore, male courtship behaviours obtained in response to the robotic replica exhibiting light stimuli were compara- ble with responses towards authentic conspecific females. Our biomimetic approach to establish ani- mal–robot individual interaction can represent an advanced strategy for trait-based ecology investiga- tion, a rapidly developing research field. Keywords Aggression Á Animal–robot interaction Á Bioinspired robotics Á Courtship behaviour Á Siamese fighting fish Introduction The decision-making process in animal sexual selec- tion is largely regulated by specific signals displayed during courtship and mating behaviour (Darwin, 1871; Sichlau et al., 2015; Benelli & Romano, 2018). The evaluation of male genetic quality and resource- holding potential by females, based on stereotyped courtship displays as well as features such as body size, colouration, and sound, is widely spread in the animal kingdom (Zahavi, 1975; Hamilton & Zuk, 1982; Bischoff et al. 1985; Ho ¨glund & Lundberg, Handling editor: I. A. Nagelkerken D. Romano (&) Á G. Benelli Á C. Stefanini The BioRobotics Institute, Sant’Anna School of Advanced Studies, viale Rinaldo Piaggio 34, Pontedera, 56025 Pisa, Italy e-mail: donato.romano@santannapisa.it G. Benelli Department of Agriculture, Food and Environment, University of Pisa, via del Borghetto 80, 56124 Pisa, Italy J.-S. Hwang Institute of Marine Biology, National Taiwan Ocean University, Keelung, Taiwan C. Stefanini Healthcare Engineering Innovation Center (HEIC), Khalifa University, Abu Dhabi, United Arab Emirates 123 Hydrobiologia (2019) 833:185–196 https://doi.org/10.1007/s10750-019-3899-6