Ch.7

Question 1

Osteichthyes

Answer 1

(osteon = bone, ichthyes = fish)

All have an internal skeleton with ossified endochondral bone in addition to dermal and Perichondral bone seen in more Basel gnathostomes

Question 2

Acintopterygii

Answer 2

Ray-finned fishes
(aktis = ray, pteron = fin/wing)

• Basal lineages with low diversity
• Derived Teleostei highly diverse

Characters
• Single dorsal fin* (can split into multiple finlets, or presence of 2nd fin)
• Cerebral hemispheres develop outwardly
• Ganoine (tissue deposited in scales, rigidity is ancestral, similar to dentine), a shiny enamel-like tissue (termed ancestral enamel)
• Ganoid scales are bony rhomboid-shaped scales covered with a shiny layer of ganoine.

Question 3

Osteichthyan characters
Bones

Answer 3

Endochondral bone
• Bony tissue replaces cartilaginous precursor

• Dermal skull bones
• Grow within dermis
• Many, many bones in fishes

Significant bones include
• Premaxilla (anterior tooth bearing dermal bone in the upper jaw)
• Maxilla (main upper bone, posterior tooth bearing dermal bone in the upper jaw)
• Dentary (posterior dermal bone forming the anterior part of the lower jaw)
• Operculum (covers exit of pharyngeal region (gills))

Question 4

Osteichthyan characters
Fins, scales, lung

Answer 4

• Fins tribasic ancestrally
• Basal elements get reduced

Lepidotrichia
• Stacks of segmented elements
• Support the fins
• Can split distally
• dermal bone

Lung ventral to gut
• Aid in both gas exchange and buoyancy

Question 5

Teleostei

Answer 5

Teleostei (teleios = complete, osteon = bone)

Question 6

Teleost characters
Fins

Answer 6

• Homocercal caudal fin
• Appears symmetrical externally
• Heterocercal caudal fin ancestral within Actinopterygii
• Asymmetrical both externally and internally

Question 7

Teleost characters
Mouth

Answer 7

• Mobile premaxilla
• Maxilla and dentary can become mobile too
• Allows for suction feeding

Only connected by soft tissue
Mouth cavity has increased, water pressure goes down —> water get sucked in.

Good for smaller organisms because greater force on them

Jaws that go up and down have more teeth because of this water pressure effect when they close their mouth, it pushes water out.

Question 8

Teleost characters
Scales

Answer 8

Cycloid scales
• Thinner than ganoid scales
• Composed of bone, no enamel- like tissues
• Allow for greater flexibility

Ctenoid scales
• Present in most derived teleosts
• Similar composition, but with posterior “comb” structure (helps with how water moves around them)

Most of each scale is embedded in the dermis with only some of it exposed. Exposed parts overlap like shingles on a roof a pattern described as imbricated.
- together thinner scales and imbrication make Teleosts body far more flexible during swimming.

Question 9

Teleost characters
Lung and gas blabber

Answer 9

• Lung develops into gas bladder
• Migrates dorsally

• Physostomous gas bladders are connected to digestive tract

• Physoclistous gas bladders are connected to circulatory system (present in most derived telesosts)

Question 10

Acanthopterygii

Answer 10

(acanth = spine, pteron = fin)

Question 11

Acanthopterygian characters
Fins

Answer 11

• Fins with bony spines (dorsal, anal and pelvic)
- spines support the first part of the dorsal fin
• Pectoral fin located laterally directly behind the operculum
• Pectoral girdle becomes vertical (closely associated with the pectoral girdle)
• Pelvic fin shifts anteriorly (in the thoracic position)
• Maxilla and dentary lose teeth

Question 12

Swimming
Body aspect

Answer 12

• Thrust generated by body – axial locomotion – or limbs – appendicular locomotion
• Axial locomotion forms a spectrum from full-body undulations to tail oscillations
• Thunniform is more efficient than anguilliform

Undulation
Anguilliform (eels)
Subcarangiform
Caragiform
Thunniform (tuna, fusiform)
Ostraciiform
Oscillation

Question 13

Swimming
Fins

Answer 13

• Fins can provide propulsion
• Undulations in dorsal or anal fins
• Crescent-shaped homocercal caudal fins produce maximum, efficient thrust
• Posteriorly positioned fins best for rapid acceleration

Fins for undulatory swimming
Dorsal, anal, dorsal and Anal together

Fins for oscillatory swimming
Labriform (rowing motion involving only short pectoral fins)
Balistiform (simultaneous undulation of dorsal and anal fins)
Moliform (roughly same thing as above)

Question 14

Swimming physics

Answer 14

Viscosity
• Greater impact on smaller fish

Drag
• Viscous drag: impacted by surface area and surface texture
• Pressure drag: impacted by shape and speed

Many fast swimmers have converged on fusiform or thunniform body shape (teardrop structure)

Question 15

Swimming stability

Answer 15

• Fins provide stability by increasing resistance in certain planes

Roll is when body is kept straight but rotates onto its side

Yaw is when the body turns left or right

Pitch is when the body moves up or down

Question 16

Oviparity

Answer 16

• Most fishes are oviparous (lay eggs)
• Some make nests or attach eggs to substrate
• Some release gametes into water column

Question 17

Viviparity

Answer 17

• live birth
• Relatively rare in fishes
• Required internal fertilization
• Range in brood sizes

Question 18

Fish larvae

Answer 18

• Larval stages can look entirely different from adult form
• Also, different diets and locomotion from adults
• Undergo one or multiple metamorphoses

Question 19

Sex determination

Gonochorism

Answer 19

sex is set at birth and does not change

Question 20

Sex determination

Protandry

Answer 20

juveniles develop as male, can become female

Question 21

Sex determination

Protogyny

Answer 21

juveniles develop as female, can become male

Question 22

Sex determination

Simultaneous hermaphroditism

Answer 22

individuals have both functional ovaries and testes

Question 23

Marine water column

Answer 23

• Majority of species and biomass concentrated within 1,000 meters of surface
• Deep water species have sensory and feeding adaptations to find and take advantage of rare food opportunities
• No teleosts found below 8,300 m

Question 24

Photic zone

Answer 24

• Photic zone fish communities shaped by organisms that make the “substrate”
• Corals and other reef builders
• Kelps and other macro algae
• Light levels determine what organisms form the substrate
• Some fish migrate between zones

Question 25

Niche partitioning drives speciation

Answer 25

East African Rift System

Cichlid fishes
• Acanthopterygians with global distribution
• Abundant and diverse in lakes of East African Rift System
• Speciation has occurred rapidly (<1,000,000 years, maybe <250,000 years)

What drives this speciation?
• Niche partitioning – using different aspects of the environment to reduce competition
• Different feeding specializations
• Unique pharyngeal jaw structures
• Breeding with similar feeders

Results in very high diversity

Question 26

Key Concepts

Answer 26

• Actinopterygii is an incredibly diverse group, united by fin, scale, and nervous system characters.
• Fishes swim via propulsion from their bodies and/or their fins.
• Fish larvae look quite different from the adult forms and have different ecologies.
• Light levels at different water depths determine what substrate- forming organisms can survive, which create different environments that fish can inhabit.