Seasonal changes in frequencies of wrestling among 16 adult river otters (Lutra canadensis) in six different captive groups (two groups of four animals and four groups of two) were investigated. Initiators of wrestling and choice of wrestling partners were identified. All otters wrestled, some as often as 15–20 bouts/h. They wrestled significantly less often during the breeding season than in months preceding the breeding season. Females and males wrestled at similar rates, but mixed-sex wrestling bouts were initiated by females almost twice as often as by males. In same-sex bouts, dominant otters initiated wrestling nearly 5 times as often as subordinates.