Biodiversity 5: Fish

Question 1

What were the ancient jawless fish called?

Answer 1

Ostracoderms ‘shell-skinned’

Question 2

Describe the Ostracoderms

Answer 2

Dominated 450-375 mil years ago
Went extinct ~150 mil years ago, outcompeted by jawed fish
Heavily armoured
Covered with bony plates and scales surfaced in dentine and enamel (Protection)
Plates around mouth probably acted as a scoop for shovelling food into mouth
Early forms lacked pectoral fins = probably poor swimmers

Question 3

Give 2 species that are modern jawless fish

Answer 3

Hagfish and Lampreys

Question 4

Describe modern jawless fish

Answer 4

Eel-like
No armour
Skeleton cartilaginous
Protective slime production
Lack paired fins and jaws

Question 5

Describe hagfish

Answer 5

Many are scavengers that feed on dead animals
Enter body through opening and eat from inside out
Only vertebrate that are isotonic with seawater

Question 6

Describe lampreys

Answer 6

Predators/parasites of fish
Adults may be freshwater/marine
Larvae (ammocoetes) are eel shaped suspension feeders that live in send
Go through metamorphosis
Cartilaginous ‘vertebral column’

Question 7

What are jawed vertebrates called?

Answer 7

Gnathostoma

Question 8

Describe the Gnathostoma

Answer 8

Jaws
2 pairs of appendages = active roles
Developed into:
Fish: pectoral & pelvic fins
Mammals: Forelimbs & hindlimbs

Question 9

Describe the evolution of jaws

Answer 9

Hinged to work up/down unlike invertebrates
Arose from modification of skeletal rods that support the pharyngeal slits
= Shows evolution as a remodelling process, rather than a creative one

Question 10

What are ancient jawed fish called?

Answer 10

Placoderms ‘plate skinned’

Question 11

Describe the placoderms

Answer 11

Silurian to the end of the Devonian period
All extinct
Large group of predators
Heavily armoured, some with cleaver like plates for biting prey

Question 12

What are the two types of modern jawed fish called?

Answer 12

Cartilaginous Fish
Bony fish

Question 13

What are the 2 groups of cartilaginous fish

Answer 13

sharks & rays
Ratfish & chimaeras

Question 14

Describe the features of cartilaginous fish

Answer 14

• Flexible endoskeleton of cartilage (not bone!)
• Cartilaginous skeleton is a derived trait → new to that group (didn’t belong to an ancestor)
• Many are covered in small tooth-like placoid scales
• Some have acute senses adapted to predatory lifestyle
• Heterocercal tail (upper lobe bigger than lower lobe) and wing-like pectoral fins provide lift because body is negatively buoyant (heavy and no swim bladder)

Question 15

Describe the acute senses some cartilaginous fish have evolved

Answer 15

Sharp vision, not colour
Nostrils with smell receptors
Lateral line system (row of microscopic organs) for detecting pressure changes
Electroreceptive organs in the head detect electric fields

Question 16

Describe the tail and fins of cartilaginous fish

Answer 16

Heterocercal tail (upper lobe bigger than lower lobe) and wing-like pectoral fins provide lift because body is negatively buoyant (heavy and no swim bladder)

Question 17

What is the endoskeleton of bony fish made from?

Answer 17

Calcium phosphate

Question 18

What is the skin of bony fish like?

Answer 18

Flattened bony scales

Question 19

What system do bony fish use to detect pressure changes?

Answer 19

Lateral line system

Question 20

Describe the gas-sac organ in bony fish

Answer 20

→ either swim bladder or sometimes a lung
Hydrostatic organ for buoyancy
May act as an oxygen reservoir during periods of stagnation/ drought
= Don’t have to keep swimming to stay up in the water column
= Suggests bony fish derived from a murky freshwater ancestor

Question 21

Describe the gills in bony fish

Answer 21

Gills covered by an operculum, with pharyngeal muscles
Acts like bellows to keep water flowing across gills (even while fish isn’t moving)

Question 22

What type of fertilisation do most bony fish use?

Answer 22

External

Question 23

What are the 3 classes of bony fish?

Answer 23

Lobe-finned fish
Lungfish
Ray-finned fish

Question 24

What shape do all fish have? Describe it.

Answer 24

Fusiform means tapered at both ends
→ reduces drag for efficient movement in the water

(other marine organisms have convergently evolved this shape e.g penguins, seals, squid)

Question 25

Describe lobe-finned fish

Answer 25

Muscular pectoral and pelvic fins supported by extensions of the skeleton
Large bottom dwellers that may have walked on the sea bed
Coelacanth → only living species

Question 26

Describe lung-fish

Answer 26

Were dominant predators in the shallow waters of the Devonian
Have lungs and nostrils
Breathe air
Adaptation, allowing them to survive in stagnant ponds and swamps

Question 27

Describe ray-finned fish

Answer 27

Reduced scaled for increased mobility
Fins free from being wings, adapted as brakes (pectoral) or rudders (pelvic)
Homocercal tail allows better maneuverability
Evolved more efficient jaw
Maxilla now free and articulated

Question 28

What is another name for bony fish?

Answer 28

teleosts

Question 29

What are the Lake Malawi Cichlids an example of?

Answer 29

Example of great diversity and adaptive radiation

Question 30

Describe the case study of the Lake Malawi Cichlids

Answer 30

Relatively small as a body of water (when compared to the oceans)
Been isolated for 2 mil years
= 450 species of Cichlid have evolved to fill many niches in the lake
Consequence of both natural and sexual selection