Aggressive behaviour in moray eels versus species identity: Do I oust you, or do I eat you?

Abstract

Abstract Observing a fight between two snowflake eels in southern Taiwan, we had difficulties locating scientific information on eel-eel aggressive behaviour and looked further afield. We collected and scored 34 videos posted on social media, to provide more insight into this behaviour. The videos showed 12 different species of moray to fight, with the genus Gymnothorax contributing ~ 71% of the films, Echidna to 24%. 82% of the retrieved videos showed same-species encounters. Fights involved “knotting”, when opponents curl around each other and shove with their bodies, and some biting. Overall, incidence of injury and death of losers, as well as injury of winners, was higher in smaller opponents. Conspecificity created the largest difference in behaviour. Available same-species encounters were interpreted as rivalry, as in our video. This normally included a visible resource the opponents fought over (a den, a food item, a mate). Same-species fights started after gaping mouths at each other, with individuals being roughly equal in size. Conspecific opponents were often injured, but never killed. Available videos with fights between different species showed predator attacks and defence in reaction. Except for one case, different-species encounters ended with one eel being killed and eaten, the winner always a fish-eating Gymnothorax species. Pre-fight, the killer was seen displaying food searching behaviour by checking holes. Both, same- and different-species fights frequently incurred deep, V-shaped wounds that were not apparently life threatening. Old V-shaped scars occurred on the bodies of some eels. Such scars could be used in research studying moray aggressive behaviour.