PADDLEFISH BUCCAL FLOW VELOCITY DURING RAM SUSPENSION-FEEDING AND RAMVENTILATION

A micro-thermistor probe was inserted into the buccal cavity of freely swimming paddlefish to measure flow velocity during ram ventilation, ram suspension feeding and prey processing. Swimming speed was measure d from videotapes recorded simultaneously with the buccal flow velocit y measurements. Both swimming velocity and buccal flow velocity were s ignificantly higher during suspension feeding than during ram ventilat ion. As the paddlefish shifted from ventilation to feeding, buccal flo w velocity increased to approximately 60 % of the swimming velocity. D uring prey processing, buccal flow velocity was significantly higher t han the swimming velocity, indicating that prey processing involves th e generation of suction. The Reynolds number (Re) for flow at the leve l of the paddlefish gill rakers during feeding is about 30, an order o f magnitude lower than the Re calculated previously for pump suspensio n-feeding blackfish. These data, combined with data available from the literature, indicate that the gill rakers of ram suspension-feeding t eleost fishes may operate at a substantially lower Re than the rakers of pump suspension feeders.