Morphology of Locomotion

Viscous drag

friction between body and water and is influenced by smoothness and surface area, influenced by body and fin size, shape, and fin placement on the body

inertial drag

caused by pressure differences resulting from the displacement of water as body moves through it, this drag increases with speed and so also impacted by body shape

why are fish fish shaped

tear drop or torpedo shaped body makes more laminar flow over body surface minimizing wake or inertail drag

What is unique about fish muscles

they are layerd not bundled, and muscle segments are not flat but have a 3D strucutre that interlock

collagenous septa

critically important for fish movement similar to tendons in other vertebrates

median septum

occur vertically on the long axis of the fish, separating the left and right muscles

main horizontal septum

separates the epaxial muscles from the hypaxial muscles

aspect ratio of the caudal fin

relationship between height and surface area of caudal fin, high AR = reduces drag and flex in caudal region (rapid sustained propulsion), Low AR = broad surface area with powerful thrusts (fast starts)

Undulation

sinusoidal wave passing down the body

oscillation

no waves along the body, trunk stays rigid structures are moved back and forth to generate thrust

Anguilliform

typical of elongated body shapes, most of body contributes to propulsion by undulation, relatively slow and awkward but good for swimmin around structures, digging and hiding, many fish begin as this

Subcarangiform

movement still undulatory but engages less of the body, low AR good for rapid starts from dead stops good for ambush predators

carangiform

body shape becoming more laterally compressed and more tear droped, less drag and higher rigidity with greater thrust and speed, higher AR

functional hinges

maintains tail at ideal angle for more consistent power stroke, substaintially reduces inertial drag

thunniform

body shape perfected for high speed, extreme body rigidity and narrow necking reduce viscous and inertial drag VERY high AR

Ostraciiform

body shape varies substantially, propurlusion mainly through tail movment back and forth (oscillatory)

tetraodontiform

body shape variable but clear medial fins, oscillatory synchronous or asynchronous movment of anal and dorsal fins

balistiform

similar to tetraodontiform but with more undulation of fins rather than oscillation

diodontiform

undulation of anal, dorsal, and pectoral fins

Rajiform

undulation of pectoral fins in skates and rays

amiiform

main propulsive power from undulating dorsal fin (not great swimmers)

gymnotiform

main propulsive power from undulating anal fin

Labriform

body typically more laterally compressed fish with important fins, mostly pectoral fin based oscillatory mvmts, power stroke provides strong propulsion recovery stroke provides lift