Bony fishes (Osteichthyes)

Question 1

What are the features of the Actinopterygii (ray finned fish)

Give some examples

Answer 1

(most are teleosts)
- Lack endochondral bone
- Loss of scales
- Upper jaw isn’t fused to cranium
- Gas bladder

Examples: Sturgeon, Paddlefish

Question 2

Describe the teleosts jaw

Answer 2

→ unfused and flexible premaxilla and maxilla = not attached to cranium
- Allowed for specialisation of feeding mechanisms
- Flexibility of bones of skull and jaws → exploit range of prey
- Jaws: suction device increased vol of buccal cavity

Question 3

What has allowed for the huge diversity in skull shape in Telosts (especially chichlids and wrasses)?

Answer 3

• Differences allowed by development of Pharyngeal jaws
• Branchial arches modified
• Freed oral jaws for food manipulation
  = diversity of feeding modes and therefore diets in Cichlids and Wrasses

Question 4

Give an example of an organism with extremely modified pharyngeal jaws

Answer 4

Moray Eel = raptorial jaws

Question 5

Name some key features of the teleosts

Answer 5

Homocercal tail
Small scales
Fusiform shape
Most are oviparous

Question 6

Describe the sensory organs in bony fish

Answer 6

Lateral line
Neuromast organs
Detects water displacement/turbulence
Fish that form shoals have lateral line organs in head

Self recognition
Cleaner wrasse pass the Mark Test → Kohda et al (2023)

Question 7

Describe the swim bladder in bony fish

Answer 7

• Used to maintain buoyancy
• Originally functioned as a lung!
• Homologous with lungs of Sarcopterygians (lobe finned fishes)
• Basal Actinopterygians → ventral and used for air breathing –
• Evolved to be dorsal

Question 8

Describe how a swim bladder works

Answer 8

If Swim Bladder attached to gut:
To increase air: fish gulps air at surface
To decrease: burps it out

If unattached to gut:
To increase: Takes up O2 from blood (complex process)
To decrease: O2 diffuses into blood and is removed from gills

Question 9

Describe how bony fish use gills

Answer 9

• Water in through mouth, over gills and out through operculum
• Buccopharyngeal pumping → slight movement of mouth and pharynx to allow water to flow in
• Countercurrent exchange:
  Blood and water flow across lamellae in opposite directions
  Maximises amount of O2 taken up by the blood