In the larval stage of the parasitic copepod Lepeophtheirus salmonis , the free living copepodid must locate and settle on a salmonid host. Chemosensory mechanisms play a role in determining whether a potential host is suitable for attachment, yet the full suite of chemical cues and resulting behavioral mechanisms used for host location and aggregation are unknown. After maturing, pre-adult females and adult male sea lice emit sex pheromones. Once mated, gravid females reduce the production of sex pheromones. The aim of this study was to investigate the potential that cues from pre-adult female and adult male sea lice influence copepodid behavior. Behavioral bioassays were conducted with copepodids exposed to water conditioned with three stages of conspecific lice (pre-adult female, adult male, and gravid female), and Atlantic salmon (Salmo salar , L.) conditioned water. Experiments demonstrated that copepodids exposed to water conditioned with the salmon host, pre-adult female or adult male sea lice elicited behaviors characteristic of arrestment, whereas sea lice exposed to gravid female conditioned water did not. These results suggest that L. salmonis larvae respond to the cues of lice stages known to produce sex pheromones, and we conjecture that they may serve to aggregate conspecifics and amplify infestations.