Ch.7 Flashcards
Osteichthyes
(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
Acintopterygii
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.
Osteichthyan characters
Bones
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))
Osteichthyan characters
Fins, scales, lung
• 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
Teleostei
Teleostei (teleios = complete, osteon = bone)
Teleost characters
Fins
• Homocercal caudal fin
• Appears symmetrical externally
• Heterocercal caudal fin ancestral within Actinopterygii
• Asymmetrical both externally and internally
Teleost characters
Mouth
• 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.
Teleost characters
Scales
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.
Teleost characters
Lung and gas blabber
• 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)
Acanthopterygii
(acanth = spine, pteron = fin)
Acanthopterygian characters
Fins
• 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
Swimming
Body aspect
• 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
Swimming
Fins
• 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)
Swimming physics
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)
Swimming stability
• 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
Oviparity
• Most fishes are oviparous (lay eggs)
• Some make nests or attach eggs to substrate
• Some release gametes into water column
Viviparity
• live birth
• Relatively rare in fishes
• Required internal fertilization
• Range in brood sizes
Fish larvae
• Larval stages can look entirely different from adult form
• Also, different diets and locomotion from adults
• Undergo one or multiple metamorphoses
Sex determination
Gonochorism
sex is set at birth and does not change
Sex determination
Protandry
juveniles develop as male, can become female
Sex determination
Protogyny
juveniles develop as female, can become male
Sex determination
Simultaneous hermaphroditism
individuals have both functional ovaries and testes
Marine water column
• 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
Photic zone
• 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
Niche partitioning drives speciation
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
Key Concepts
• 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.
