LECTURE 17 - 'Fishes' part 1

Question 1

Describe the anatomy of fishes

Answer 1

• There are roughly 28,000 known species of fish today, but many more are being described every year
• Within those 28,000 species there is a huge variation in morphology

Question 2

What factors influence the morphology of fishes?

Answer 2

• There are many factory involved, but the most important is that FISH SPEND THEIR TIME IN WATER, which imposes or relaxes a number of constraints on basic physiological and morphological traits

Question 3

How does density influence the morphology of fish?

Answer 3

• Water has a density 800x that of air, and it is 70x as viscous
• These properties select for streamlined shapes that reduce drag and turbulence
• Drag increases with the speed of an object or the current, and is due to the boundary layer around the object changing from laminar to turbulent flow

Question 4

How does buoyancy influence the morphology of fish?

Answer 4

• Water provides buoyancy support, which means fish don’t require heavy bones to counteract gravity
• Many bony fish posses an internal gas-filled organ called a swim bladder that allows them to control their buoyancy

Question 5

What are the two different types of swim bladder?

Answer 5

• Physostomous
• Physoclistous

Question 6

What are the three ways fins can be used as “foils”?

Answer 6

• To rise
• To hold
• To sink

Question 7

How does the lateral line influence the morphology of fish?

Answer 7

• The density of water also helps fish to detect movement vibration, and pressure gradients in the environment surrounding the animal
• Fish can use the lateral line sensory system to determine the direction and rate of water movement and to orient themselves in a water current (rheotaxis)

Question 8

How does suction feeding influence the morphology of fish?

Answer 8

• Incompressibility of water allows suction feeding, which is very common in many bony fish
• Suction feeding leads to prey capture through rapid movements that create a drop in pressure in the buccal cavity and cause the water in front of the mouth to rush into the oral cavity, entrapping the prey in its flow

Question 9

How does depth influence the morphology of fish?

Answer 9

• Low light penetrability: below 1000m there is no light, which restricts productivity to the euphotic zone
• Fish often rely on senses besides eyesight to detect prey and avoid predators
• Many fish can produce their own light through bioluminescence
• Every 10m of depth = 1 atm of pressure
• Selects for watery, incompressible tissue (reduced calcification and muscle)

Question 10

How does low oxygen availability influence the morphology of fish?

Answer 10

• Very low oxygen saturation relative to air, so gills must be efficient to extract it
• Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills
• Countercurrent flow in gills
  
  • Exchange is more complete with countercurrent flow
  • In the countercurent exchanges, the water is always more saturated than the blood so that a gradient of O2 saturation exists over the full length of exchange surfaces

Question 11

How does ventilation in the gills work?

Answer 11

• Flow of water over the gills of fishes is maintained by the action of skeletal muscle pumps
• Many active fish ram-ventilate their gills; they open their mouths to ventilate the gills by the forward motion of the body while swimming

Question 12

What are the physics of swimming?

Answer 12

• against current force = DRAG
• along current force = THRUST
• force pulling down = gravity
• force pushing up = buoyancy and lift
• Roll = when the fish’s body waddles from side to side while swimming
• Yaw = when the fish turns its head from side to side (like shaking your head)
• Pitch = when the fish bobs his head up and down (like nodding in humans)

NEED TO:
- Generate thrust/minimize drag
- Generate lift/overcome gravity

• Drag can be reduced by streamlining the body to a low aspect ratio
• Reduce viscous drag by increasing surface smoothness (scale design or loss of scales)
  
  • aspect ratio = a/b

Question 13

What are the different body/caudal fin propulsion (BCF) names?

Answer 13

FROM UNDULATORY TO OSCILLATORY
- Anguilliform
- Subcarangiform
- Carangiform
- Thunniform
- Ostraciiform

Question 14

What are the different median/paired fin propulsion (MPF) names?

Answer 14

UNDULATORY FIN MOTIONS
- PECTORAL
- Rajiform
- Diodontiform
- OSCILLATORY FIN MOTIONS
- Labriform
- DORSAL
- Amiiform
- ANAL
- Gymnotiform
- ANAL AND DORSAL
- Balistiform
- OSCILLATORY FIN MOTIONS
- Tetraodontiform

Question 15

Describe Anguilliform.

Answer 15

• e.g., moray eel
• Entire body undulates
• Several wavelengths in body
• Inefficient

Question 16

Describe Subcarangiform.

Answer 16

• e.g. rainbow trout
• Swim with posterior portion of body, less than one wavelength
• Tend toward truncate rounded tails with low aspect ratio (~1.5-2)

Question 17

Describe Carangiform.

Answer 17

• e.g., Jacks
• Less than half the body flexes
• Generally narrow peduncle, flared and strongly forked tail with high aspect ratio (~3.5)

Question 18

Describe Thunniform.

Answer 18

• e.g., tuna
• Extremely stiff body
• Narrow peduncle, flared and strongly forked tail with very high aspect ratio (~4-10)

Question 19

Describe Ostraciiform

Answer 19

• e.g., cowfish
• completely rigid body
• uses just the tail for propulsion

Question 20

Describe Rajiiform

Answer 20

• e.g., manta ray
• Undulate pectoral fins from front to back
• more than one wavelength present in pectoral fin

Question 21

Describe Diodontiform

Answer 21

• e.g., pufferfish
• undulate pectoral fins for sculling and maneuvering

Question 22

Describe Labriform

Answer 22

• e.g., parrotfish
• Oscillate pectoral fins for sculling and maneuvering

Question 23

Describe amiiform/gymnotiform

Answer 23

• e.g., knifefish
• undulatory waves of dorsal or anal fins

Question 24

Describe Balistiform

Answer 24

• e.g. triggerfish
• use simultaneous motion of dorsal and anal fins

Question 25

Describe Tetraodontiform

Answer 25

• e.g., mola mola
• Both dorsal and anal fins oscillate together

Question 26

What are the different tail designs?

Answer 26

• Hypocercal
• Heterocercal (epicercal)
• Homocercal

Question 27

What are some non-swimming locomotion styles?

Answer 27

• Jet propulsion (e.g., sculpins)
• Passive drift (e.g., larvae, sargassum fish)
• Flying (e.g., flying fish)
• Leaping (e.g., mullets, tuna, and sailfish)
• Burrowing (e.g., eels, gobies, flatfish, rays)
• Hitchhiking (e.g., remoras, lamprey)
• Walking on land (e.g., mudskippers, walking catfish)
• Walking on the bottom (e.g., sea robins, batfish)

Question 28

(IN CHORDATA) What are Myxinoidea?

Answer 28

• Hagfish
• 43 species
• Only living animals with a skull but no vertebrae
• Until recently, it was unclear if they lost the vertebral column or represent an evolutionary stage within Craniata that precedes the evolution of vertebrae
• New evidence suggest monophyly of the Cystostomes and thus that hagfish underwent degeneracy since their divergence from other vertebrates
• No jaws, no paired fins
• Average ~0.5m length
• Rudimentary eyes
• Accessory “hearts”
• Mucous production (up to 20L)
• Knot-tying feeding and anti-predator behaviour
• Temperate marine habitat
• Typically benthic (>25m depth)
• Scavengers

Question 29

(IN CHORDATA) What are Petromyzontoidea?

Answer 29

• Lampreys
• 41 species
• Range from ~10-100cm in length
• No jaws, use “oral disc” instead
• Large eyes, single nostril
• Freshwater or anadromous
• Very distinct larval form (ammocyete)
• About half of species are parasitic as adults, others do not feed as adults