Agonistic interactions between slender mudskippers (Periophthalmus gracilis) in Singapore

Mudskippers engage in frequent territorial interactions. Few studies of mudskipper agonistic behavioral sequences exist. The slender mudskipper (Periophthalmus gracilis) inhabits intertidal zones of mangrove forests across Southeast Asia. Here, we describe common behavioral sequences of winners and losers among unmanipulated, wild slender mudskipper interactions in Singapore. Winning mudskippers showed more approach behaviors than losers, such as "Crawl towards", and more behaviors that may indicate aggression, such as "Pectoral wave", "Flag", and "Head up". Losers showed more evasive behaviors, like "Jump" and "Crawl away". We found evidence of agonistic behavioral matching. Larger mudskippers won contests more frequently than smaller mudskippers.