Lecture 17

Question 1

Protochordata, Craniata, Gnathostomata

Answer 1

All are within Phylum Chordata

• Protochordata
• Do not have a true brain, skull, or vertebral column
• Craniata (i.e. Vertebrata)
• Have a skull (cranium) and/or vertebral column
• Agnatha (Hagfish and Lampreys) only have a skull (no vertebrae)
• Gnathostomata
• Craniates with jaws
• Includes all of Craniata except for Agnatha

Question 2

Phylogeny of fish!

Answer 2

fish itself is any non tetrapod vertebrate

Agnatha
Osteichthyes* (Bony Fishes)
Chondrichthyes

Question 3

General characteristics to distinguish what is a fish (5)

Answer 3

• Form
• Locomotion in water
• Neutral buoyancy and the swim bladder
• Respiration
• Osmotic regulation

Question 4

Form – types of scales for fish

Answer 4

• Placoid scales
• Ganoid scales
• Cycloid and Ctenoid scales

Question 5

Placoid scales

Answer 5

• Small, conical, toothlike structures
• Typical of chondrichthyes
• Modified to teeth in sharks

Question 6

Ganoid scales

Answer 6

• Diamond shaped

* Early bony fishes and living gars

Question 7

Cycloid and Ctenoid scales

Answer 7

• Arranged in overlapping rows

* Typical of teleost fish

Question 8

Locomotion in Water for fish

Answer 8

Movement achieved through undulation of the posterior end
• Generates thrust (forward motion) and lateral force (sideways motion)
• The lateral force causes fish head to “yaw”, or deviate in the same direction as the tail
• The “yaw” occurs more in more flexible fish
• A less flexible body plan is conducive to speed!!!!!!!!!!!!!!!

Question 9

Buoyancy in fish

Answer 9

Swim bladder = gas-filled organ
Volume adjusted for neutral buoyancy

present in most pelagic (open sea) bony fishes

Not in very deep fish, and most bottom-dwellers

Question 10

Why don’t Chondricthyes (e.g. sharks) have no swim bladder

Answer 10

• Asymmetrical tail provides lift,

* Large livers with squalene (particularly buoyant lipid)

Question 11

Respiration for fish

Answer 11

Most fish use gills
• Breathe dissolved oxygen (oxygen that is in the water)
• Gills are located in the pharyngeal cavity
• Gills are covered with an operculum in bony fishes
• Increases efficiency of respiration
• Not present in sharks and rays
• Some fish also have lungs ,Capable of breathing air

Question 12

Gills in fish

Answer 12

• Gill composed of thin filaments covered with an epidermal membrane
• The membrane is folded repeatedly into plate-like lamellae
• Enormous surface area
• Lamellae contain main blood capillaries
• Water is pumped continuously in the mouth, over the gills and out through the gill slits
• Gas exchange occurs across thin walls of blood capillaries

Question 13

Osmotic Regulation in fish

Answer 13

• Maintenance of balance of fluids
• Freshwater and Marine fish have opposite challenges
• Freshwater fish are hyperosmotic regulators
• Marine fish are hypoosmotic regulators

Question 14

Hyperosmotic Regulators

Answer 14

Freshwater fish
• Greater salt concentration in fish than in surrounding water
• Scales and mucous protect the fish, but water can enter across membranes (e.g. gills)
• Water pumped out by kidneys
• Salt-absorbing cells in the gill move salt from water to blood

Question 15

Hypoosmotic Regulators

Answer 15

• Marine fish
• Contain a smaller concentration of salt than surrounding water
• Salt-secretory cells in the gill move salt out of body
• Salt is voided with feces or excreted by the kidney

Question 16

Agnatha - Hagfishes caracteristics

Answer 16

• Jawless
• Entirely marine group
• Feed on annelids, molluscs, crustaceans, and dead or dying fishes
• Scavengers and predators (not parasitic)
• Poorly developed eyes
• Keenly developed sense of smell and touch
• Produce slime as a defence mechanism

Question 17

Feeding and movement of hagfish

Answer 17

Agnatha
• Hagfish rasps bits of flesh from its prey
• Keratinized plates on tongue • Can itself into knot
• Passes the knot forward along its body until it is pressed securely against the side of its prey (for leverage)

Question 18

Agnatha - Lamprey carcteristics

Answer 18

• Half are parasitic

* They use tooth-like plates of keratin for rasping a hole, through which fluids and tissues are sucked.

Question 19

Chondrichthyes carcteristics

Answer 19

• Cartilaginous fishes (sharks, rays, chimaeras)
• Cartilaginous skeleton
• Bone entirely absent
• Placoid scales
• No swim bladder

Question 20

Chondrichthyes species

Answer 20

Rays: skates, stingrays, electric rays, and manta rays
• Dorsoventrally flattened bodies

Chimaeras (also called ratfishes)
• Closest living relatives are sharks
• Instead of teeth their jaws bear large flat plates

Sharks
• Apex predators – most feed at the top of the
marine food chain
• Some exceptions: e.g. whale shark – largest extant fish species (up to 15 m) – is slow-moving and feeds on plankton
• Spined pigmy shark – 28 cm – feeds on small fishes

Question 21

Sharks body plan

Answer 21

• Asymmetrical heterocercal tail
• Vertebral column turns upward and extends into the dorsal lobe of
the tale
• Provides lift as the shark swims
• Must constantly move to avoid sinking (even while sleeping!)

Question 22

Osteichthyes

Answer 22

• Bony Fish
• Bone replaces cartilage
• 2 groups
• Ray-finned fishes & Lobe-finned fishes
• Gas-filled pouch branches from esophagus
• In fish that use these pouches primarily for gas exchange, they are
called lungs
• In fishes that use these pouches primarily for buoyancy, they are called swim bladders

Question 23

Gills vs Lungs

Answer 23

• Which evolved first? Probably gills, but lungs also evolved early
• Ancestor of ray-finned and lobe-finned fishes had gills and lungs

In lobe-finned fishes (and tetrapods) lungs were preserved
• Modern lobe-finned fish also retained gills
• In ray-finned fishes, gills were preserved and lungs were adapted into swim bladder

Question 24

Ray-finned fishes

Answer 24

• Symmetrical homocercal tail allows for greater speed

* Permitted by the swim bladder and improved control of buoyancy

Question 25

Lobe-finned fishes

Answer 25

* Small group * 6 species of lungfishes * 2 species of coelacanths * Ancestor of tetrapods is found within an extinct lineage of this group * Lobe fins with a single bone that articulates with rest of body * Diphycercal tails * Lungs and gills

Question 26

Lungfishes

Answer 26

* Can live out of water for extended periods of time | * E.g. African lungfishes live in streambeds during the dry season. They remain dormant until rain returns.