Within species variation across males is common among vertebrates and is often related to distinct reproductive strategies characterized by dramatic differences in morphology and behavior. Males with divergent reproductive tactics often use communication signals in a status-dependent way. South American weakly electric knifefish are an excellent model in which to study how male variation in morphology underlies differences in social communication during intermale contests. Knifefish produce a continuous electric organ discharge (EOD) from their tail to communicate. Fish can also transiently modulate the frequency of this discharge during courtship and agonistic encounters to produce signals called chirps. Variation in male jaw morphology is common among male knifefish and is sometimes related to variation in electrocommunication. In one species, Compsaraia samueli, males show striking variation in jaw length. However, EODs and chirps have never been investigated in this species, so it is unclear if jaw length is related to the production and function of chirps. Here, we use live, agonistic, dyadic encounters with males of varying jaw lengths to analyze the function of chirps. The male with longer jaws was more likely to be dominant and attacked more. Chirp rate was also positively correlated with attack rate within and between fish. Within both dominants and subordinates, chirps tended to precede attacks with a latency of 1-2s, suggesting chirps serve as aggressive signals in C. samueli. Even though males produced chirps in a status-dependent way, their function did not vary across status. Together, these results confirm variation in male morphology determines differences in aggression and communication.