Pectoral fin kinematics and electromyography in Karman gaiting trout

Pectoral fin activity is important for a range of behaviors in fishes, including propulsion and maneuvering. How these paired fins are used to navigate unsteady flows is less understood, despite their prominent use in stream-dwelling fishes such as rainbow trout (Oncorhynchus mykiss). We investigated the muscle activity of pectoral fins in four trout (L= 21.7 ±0.837 cm) Karman Gaiting behind a 5 cm D-cylinder across a range of five flow speeds (2 L s-1 – 3.75 L s-1). Electromyography recordings for both the superficial and deep layers of the pectoral fin abductor and adductor muscles were collected with simultaneous high-speed video to reconstruct pectoral fin motion and muscle activity. Pectoral fin motions were observed during Karman Gaiting which co-occurred with activity from the abductor muscles. Our data suggest that Karman Gaiting fish use their pectoral fins to interact with vortical flows in a manner that allows them to employ passive or trimming forces to adjust their position. When a major body correction is needed, especially when fish were re-positioning themselves or re-entering the vortex street at high speeds, both the abductor and adductor muscles are highly active. At high flows, adductors and abductors showed the highest activity when coinciding with the initiation of braking motions, which occurred when trout approached the cylinder suction zone.