Fish Locomotion

Swimming by Fishes Most economical form of movement by animals Bouyed by water No energy needed to counter gravity

Swimming by Fishes Squirrel - 1 km walk - 5.43 kcal Gull - 1 km flight - 1.45 kcal Salmon - 1 km swim - 0.39 kcal

3 types of swimming Sustained swimming - slow Burst swimming - fast Prolonged swimming - medium

3 types of swimming Sustained swimming - slow - 6-7 body lengths per second Foraging over large areas, long-distance migrations Aerobic - no oxygen debt

3 types of swimming Burst swimming - fast - up to 20 body lengths per second Escaping predators, capturing prey, swimming against currents Anaerobic - oxygen debt

3 types of swimming Prolonged swimming - intermediate - ~ 10 body lengths per second Used as situation demands Aerobic and anaerobic

Locomotion Most locomotion accomplished through use of caudal fin Fastest fish - barracuda - 27 mph

Locomotion Propulsive muscles along side of fish are W-shaped myomeres (myotomes)

Locomotion Moves by contraction waves of myomeres moving posterior along one side Creates sinusoidal movement of body by alternating contractions on one side of body, then the other

Fish Locomotion Primary forces involved in fish swimming: Thrust - force that propels forward Drag - friction produced from passing an object through a medium Gravity – force from earth’s magnetic pull (partially counterbalanced by density of water) Lift - upward force that counteracts gravity

Swimming Styles - Thrust Generation Body waves – Anguilliform Partial body waves – (Sub)Carangiform Caudal peduncle/fin beats – Ostraciform Medial fin waves - Amiiform Pectoral fin beats -Labriform

Swimming Styles Body waves Anguilliform (eel-like) Lateral curvature in spine and musculature that moves in a posterior direction Start: lateral displacement of head, and then passage of this displacement along the body axis to the tail Result: backward-facing “wall” of body pushing against the water

Swimming Styles Partial body waves (Sub) Carangiform, Thunniform (tuna-like) Body wave begins posterior to head and increases with amplitude as it moves posteriorly Reduced drag compared to full body wave swimming Wave STARTS at the caudal peducle (deeply forked, lunate)

Swimming Styles Caudal peduncle/fin beats Ostraciform (boxfish-like and puffer-like) Sculling action of caudal fin—like rowing No body waves - body remains rigid - useful for odd-shaped fishes

Swimming Styles Medial fin waves Amiiform - bowfin-like Body rigid, but medial fins generate posterior waves (forward) or anterior (reverse) Good for stalking or moving without disrupting body musculature that serves as electric organ (knifefish) Also used for sculling - triggerfish & others

Swimming Styles Pectoral fin beats Labriform wrasse-like Similar to rowing laterally-positioned pectoral fins- often includes feathering as well Especially useful for fine maneuvering e.g. by deep-bodied fishes

Locomotion video http://www.youtube.com/watch?v=70-G1eEZC_o

Drag Reduction Features in Fish Fusiform body shape Reduction of body wave amplitude Reduction of fin surface area: caudal fin (forked, lunate) paired and medial fins Boundary layer modifications mucous laminar jets of water microprojections

Fusiform body shape pointed leading edge maximum depth 1/3 body length back from head posterior taper “propeller” (caudal fin) interrupts perfect fusiform shape

Body wave modifications Minimize lateral movement of head to reduce drag - subcarangiform Increase amplitude as wave moves in posterior direction Ultimate expression involves no body waves, but alternate contraction and transfer of body musculature energy to caudal peduncle and caudal fin - thunniform

Fin surface area reduction Area of fins increases drag Permanent design modifications: forked caudal fins, reduced length of medial fins Adjustable design modifications: variable erection of fins - allows for minimizing surface area when fin is not needed for thrust or turning - ultimate expression: fairings in tunas (dorsal and pectoral fin pockets)

Boundary layer modification Layer of water immediately adjacent to skin causes most of friction - boundary layer Thickness of boundary layer is proportional to amount of friction Three approaches to reducing thickness of boundary layer: smoothing it - making it “slicker” roughing it - giving it tiny disruptions (golfers learned from sharks??) shortening it - reducing distance of contact

Boundary Layer, continued Fluid jets - from gill chamber and out operculum or in micropockets behind and beneath scales Mucous - slime adds to “slipperiness”, can reduce drag by up to 65% Microprojections - disrupt boundary layer so it cannot grow: ctenae placoid tips

Buoyancy Control in Fishes Dynamic lift: generated by propelling a hydrofoil forward at an inclined angle of attack Static lift: generated by including low-density substances and reducing mass of high density substances in body.

Dynamic Lift Hydrofoils: fish use their fusiform body and some use their pectoral fins as hydrofoils Amount of lift is determined by: angle of attack and speed of propulsion Ultimate expression of this is in pelagic rovers - tunas, mackerel sharks head, pectoral fins and peduncle keels all used as hydrofoils swim constantly

Static Lift Reduction of high density substances: cartilage less dense than bone use design features in bone that increase strength while reducing mass of bone Inclusion of low-density fluids lipids - squalene in sharks (sp. grav. = 0.86) stored in liver gases - in swim bladder only in bony fishes

Swim bladders Gas-filled “appendix” to the anterior digestive system - dorsal to abdominal organs Two types of swim bladders: physostomous - pneumatic duct connects swim bladder to esophagous physoclistous - no connection between swim bladder and gut