1. Biology 201 Dr. Edwin DeMont St. Francis Xavier University Chapter 18 The Fishes: Vertebrate Success in Water Part 1

2. St. Francis Xavier University The Fishes Filmed live The locomotor structure of a fish functions to propel it through the water and helps to reduce the cost of locomotion.

3. St. Francis Xavier University No Slip Condition No flow exists at the interface of a solid and a moving fluid. Filmed live Surface of fish or Wall of artery Velocity gradient Shear forces Friction Boundary layer (b.l.) Video Skin Friction Drag Always exists Laminar or turbulent

4. St. Francis Xavier University Drag Reduction Aquatic swimmers have several different mechanisms to reduce skin friction drag. Filmed live - Riblets on scallops - Fish Slime - Riblets on sharks - Modify b.l. Laminar ↔ turbulent Human swimmers

5. St. Francis Xavier University Pressure drag Filmed live Image source Low pressureHigh pressure Pressure Drag Pressure differences create a pressure gradient → Pressure Drag Reduce pressure drag by streamlining.

6. St. Francis Xavier University Total drag Total Drag = Skin Friction Drag + Pressure Drag Total Drag → constant × V 2 Drag on body slows it down – wastes energy But – drag isn’t always bad news…

7. St. Francis Xavier University Drag as thrust Fins oscillate back and forth creating drag on the fin. What happens on the forward (recovery) stroke? During the backstroke (power) the drag force is directly forward and becomes the thrust force.

8. St. Francis Xavier University Whole Body Whole body (or caudal fin) undulations also generate thrust. Tail interacts with water to form ‘vortexes’ that move downstream and ‘push’ the fish forward.