Chapter 19: Locomotion & Buoyancy

Question 1

How are the evolutionary pressures different for vertebrates moving in land vs water?

Answer 1

Horizontal:
Fish are neutrally buoyant, excused from laws of gravity; exert greater force against water as they move through it; less energy to swim than humans;
H2O 800x more dense than O2.

Vertical:
maintaining vertical position in fluid environment requires energy constant adjustments to fins & body surfaces (swimming) or through buoyancy adjustments
(made with swim bladder).

Question 2

Explain the differences between red and white muscle cells in fishes.

Answer 2

Red muscle cells:
contain high levels of myoglobin & O2 storing proteins;
red appearance; more mitochondria & greater local capillary density; used in normal, sustained swimming activity and is fatigue resistant at slow/ cruise speeds; in highly mobile fish (tunas); extremely well vascularized (efficient O2 supply & sometimes for thermoregulation. (Sparidae, Clupeidae, Carangidae, Scombridae).

White muscle cells:
low levels myoglobin; sudden bursts of rapid swimming (escape or prey capture); operate in anaerobic mode when engaged in burst activity

Question 3

Which Families have more red muscle and why?

Answer 3

Sparidae, Clupeidae, Carangidae, Scombridae; amount of red muscle depends on mode of swimming.

Question 4

Explain the various modes of locomotion in the fish world and provide species examples.

Answer 4

BCF Gaits: Body and caudal fin propel (ex: anguilliform, subcarangiform, carangiform, thunniform, ostraciiform swimming)

MPF Gaits: Fin swimming modes are undulation (waves are propagated along fin surfaces that are broadly attached to the fish’s body) or oscillation (fins with narrower bases are sculled back and forth); locomotion using dorsal and anal fin undulation (ex: balistiform, amiiform, gymnotiform); locomotion using oscillation of dorsal and anal fins
(ex: tetraodontiform); locomotion using pectoral appendages (ex: rajiform, labriform)

Question 5

BCF Gait

Answer 5

Body and caudal fin propel

Question 6

MPF Gait

Answer 6

Fin swimming modes are undulation (waves are propagated along fin surfaces that are broadly attached to the fish’s body) or oscillation (fins with narrower bases are sculled back and forth)

Question 7

Discuss critical swimming speeds.

Answer 7

(Ucrit); maximum speed at which a fish can swim for selected interval of time; experimental animals placed in tubes through which H2O is pumped at desired speed and then increasing speed at regular intervals until fish fails to swim; typical swimming intervals range 2.5-10 body lengths per second (Ls^-1)

Question 8

Discuss larval fish speeds.

Answer 8

Larvae of coral reef fish: 13.7 Ls-1 (can be as fast as 34 Ls-1); VERY fast

Question 9

Discuss migration speeds.

Answer 9

Slower speeds; migrating fish must maintain a speed that’s energetically efficient over long distances.

Question 10

How is the swim bladder and lung homologous structures?

Answer 10

Both form as outpocketings of embryonic gut; both gas-filled bags; both share similar musculature & patterns of innervation; lungs (paired ventral structures); swim bladders (single structures occupying dorsal part of body (duh!))

Question 11

Explain the different swimbladder configurations and functions.

Answer 11

Torpedo- shaped organ, but many varieties;
Minnows/ carps (Cyprinidae): have anterior and posterior chambers connected by a sphincter.
Herrings (Clupeidae): swim bladder has posterior opening to exterior near anus (gas can be voided> fart sounds).
Physostomous: swim bladder attached to digestive system by tube.
Physoclistous: no connection to digestive system (nowhere for O2 to escape).

Question 12

Provide examples of fish that do not have swimbladders- how do they prevent sinking?

Answer 12

Pleuronectiformes (Flounder), Sharks,

Question 13

What are the advantages of having a swimbladder?

Answer 13

Buoyancy maintenance;
Sound production: most sophisticated swim bladder in Scianidae; unusual, sexually dimorphic gas bladders with various shaped sacs.
Sound reception: act as resonator; Some primitive Actinopterygians (bowfin & gar): use swim bladder as lung> in this case, swim bladder is compartmentalized and heavily vascularized.

Question 14

What are the disadvantages of having a swimbladder?

Answer 14

Buoyancy over a range of depths.

Fish descends–>increasing pressure compresses gas bladder, decreasing buoyancy.

Fish ascends–> gas bladder expands bc of decreasing pressure; bc no “relief valve” other organs crowded out by expanding gas bladder; bottom-dwelling fish hooked and brought to surface rapidly, stomachs can protrude from mouth.

Question 15

Discuss how swim bladder morphology reflects ecology and habitat of fishes.

Answer 15

Benthic fish–> small/ no gas bladder; wedge in tight places, dig in, special suction structures (maintain position).

Fish that swim up for food–> small gas bladder.

Bathypelagic species (below 1000m)–> no gas bladder.

Live @ bottom, confined activities to narrow depth ranges (marine)–> gas bladders 5-5.6% of volume (7-10.6% in freshwater species) less bc freshwater content in body makes them more buoyant.

Species adapted to flowing water–> smaller gas bladders than still water fish (less buoyant condition is favorable to maintain position in stream).

Trout & Salmon–> changes from small in stream to larger in the ocean.

Question 16

As fish vertically move through the water column, describe the mechanisms for gas resorption in the swimbladder. (Removing gas on ascent)

Answer 16

Overcome by special areas in wall where rich bed of capillaries can be exposed to lumen of gas bladder.
Resorption involves diffusion from high gas tension to lower tension in blood.
Rate governed by tensions, temperature (warm, gas expands), capillary bed area, rate of blood flow through bed. (pressure receptors that sense decrease in pressure.
Eels- pneumatic duct modified for gas resorption.
Percoid fish (pipefish, stickleback)- diaphragm separate posterior, gas-resorbing part of gas bladder from anterior, gas secreting section (Euphysoclistic)
Paraphysoclistic fish- gas secreting & diffusing areas not well separated

Question 17

As fish vertically move through the water column, describe the mechanisms for gas secretion in the swimbladder. (absorbed during descent)

Answer 17

Blood–> gas bladder thru arterial capillaries, circulates thru special bed of capillaries from which gases are secreted into gas bladder & flows away thru venous capillaries.
Bundles of capillaries–> form “rete mirable” (wonderful nets); can 300- 200,000 capillaries in rete.
Parallel alignment of small vessels form efficient counter current structure, to concentrate gases at site of gas gland.
Process of gas [] in swim bladder:
aided by lactic acid secretion into blood by gas gland–> CO2 + H2O-><- H2CO3 -><- 2H+ + CO32- (more acid in blood drives equation left)–> CO2 increases, pH decreases.–> promotes Bohr Effect (O2 not bound to hemoglobin)–> lactate ions decrease amount of gas held in sol’n, blood leaving gas gland thru venous capillaries of rete has greater partial pressure (gases, O2) than blood in arterial capillaries. Great length & # capillaries allow O2 in the capillaries to diffuse into blood which goes to swim bladder–> pressure in small vessels higher than gas bladder (gas released at gas gland) inflating the bladder!!

Question 18

Gas Bladders

Answer 18

Impervious to gas leakage (4 tough layers).
Outer layer–> densely woven fibers.
Next layer–> loosely organized fibers.
Inner 2 layers–> smooth muscle & epithelium.
Toughness allows swimbladders to be removed (deflated?) and inflated.