LEFTOVER SALMON The jam circuit has long been the province of the bluegrass/rock 'n' roll fusion - but that was hardly the case when Leftover Salmon took electric instruments to rootsy Americana more than two decades ago. The improv pioneers charmingly dub their style "polyethnic Cajun slamgrass," mashing bouncy cajun and funk rhythms with high-energy bluegrass stomp. It's a formula that works - Salmon's influence is palpable in heavy-hitters all across the plugged-in folk ouvre, including occasional collaborator String Cheese Incident. Their first studio album eight years, Aquatic Hitchhiker, drops next month. $25. Visulite Theatre.