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

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

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

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

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.

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…

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.

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.

Volume of s.b. decreases St. Francis Xavier University Buoyancy Control Several mechanisms aid in vertical regulation and include fins to create lift, changing body density by the addition of oils. Swim bladders (s.b.) are also used for buoyancy. Water pressure increases Density of fish increases Need to precisely control volume. Why?

St. Francis Xavier University Buoyancy Control Two types of swim bladder: (1) no connection to gut and (2) direct connection to gut. 2. Physostomous fishes 1. Physoclistous fishes Another diagram

St. Francis Xavier University Countercurrent Multiplier Swimbladder Gas gland Normal blood flow through rete O2O2 O2O2

St. Francis Xavier University Countercurrent Multiplier Swimbladder Gas gland Fish wants to move oxygen into Swimbladder Produces lactic acid O2O2 O2O2 O2O2 O2O2 Decreases affinity of oxygen to hemoglobin

St. Francis Xavier University Countercurrent Multiplier Swimbladder Gas gland Fish wants to move Oxygen into Swimbladder Produces lactic acid O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2

St. Francis Xavier University Countercurrent Multiplier Swimbladder Gas gland Fish wants to move Oxygen into Swimbladder Produces lactic acid O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2

St. Francis Xavier University Countercurrent Multiplier Swimbladder Fish wants to move Oxygen into Swimbladder O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2

St. Francis Xavier University Sensory Functions Photo source Sensory receptors are widely distributed and used for olfaction, vision, hearing, equilibrium and for detecting water movements. Schooling may be controlled by sensing water movement generated by nearby fish. Collision-free Driving by Mimicking Fish Behavior

St. Francis Xavier University Lateral Line The lateral line system is a set of pits that detect changes in water pressure. Why is the lateral line located here? Image source Shear forces in b.l. bend cupula Sense hairs bend and response initiated.

St. Francis Xavier University Sound Production Audio communication is not obvious in fishes, but may be used extensively. Low frequency sounds can be detected by lateral line receptors. White Grunt (Haemulon plumieri ) Picture Source

St. Francis Xavier University Atlantic Herring Photo source ‘Frt’ing Sound (at night) Contact Anti-predator (Fast Repetitive Tick) Communication: - Reduced lateral line - Swim bladder connects to inner ear and gut.

St. Francis Xavier University DVD Video Wild Moves: Insights into Animal Physiology Fish and Marine Mammals: Swimming and Diving Several questions will be raised during the video. By the end of the video, you should be able to answer the questions listed on the next slide.

St. Francis Xavier University DVD Video 1. What determines the locomotor styles of fishes? 2. How do fish change their locomotor style with speed? 3. Why do fish have two types of muscles? 4. Why do large fish swim the fastest? 5. What mechanisms do aquatic animals use to maintain themselves in the water column?