Aggressive interactions between fishes commonly take place in a social environment in which uninvolved individuals (bystanders) have an opportunity to gather information about interactants. Signals frequently used during such interactions are designed to transmit information about resource-holding power and/or intention. They are generally related to the level of escalation reached and the eventual outcome of a fight. We consider here the information available in signaling and nonsignaling aspects of aggressive interactions. We focus, in particular, on information available to bystanders. We summarize evidence that bystanders alter their behavior toward interactants on the basis of information acquired while bystanding, and we discuss the sources of information that may result in this change of behavior. In particular, we distinguish eavesdropping (i.e., extracting information from signaling interactions) as a subset of bystanding (i.e., extracting information from all available sources). We conclude that considerations of aggressive strategies should include potential costs and benefits resulting from wider social contexts in which aggression occurs.