Marine Vertebrates: Fishes (part 2)

Fishes  Phylum Chordata  Subphylum Vertebrata  3 Classes:  Class Agnatha (jawless fishes)  Class Chondrichthyes (cartilaginous fishes)  Class Osteichthyes (bony fishes)

Fishes - Anatomy  Cartilaginous fishes:  Ventral mouth  Heterocercal tail (caudal fin)  Placoid scales “dermal denticles”

 Bony fishes:  Terminal mouth  Homocercal tail  Cycloid or ctenoid scales cycloid ctenoid Fishes - Anatomy

 Cartilaginous fish skeleton: Fishes - Anatomy

 Bony fish skeleton: Fishes - Anatomy

Fishes - Buoyancy  Bony fish – swim bladder (gas)  Cartilaginous fish –  Swim, get lift from stiff fins  Large, oil-filled liver  Cartilage half as dense as bone

Fishes - Locomotion  Muscle up to 75% of body weight  Muscle bands – myomeres (flake when cooked)  Red muscle – sustained swimming  White muscle – burst swimming

Fishes - Locomotion Homocercal caudal fins by shape: Slowest → Fast → ← Fastest ← Slow Heterocercal caudal fins:

Fishes - Locomotion Swimming modes:

Fishes - Locomotion Built for speed – Pacific sailfish has high speed bursts 70+ mph

Fishes - Respiration Cartilaginous fish Bony fish (more efficient)  5-7 pairs of gills  Gill slit openings  4 pairs of gills  Operculum gill cover

Fishes - Respiration  Spiracles important for rays when buried

Fishes - Respiration Gills maximize oxygen diffusion:  High surface area  Counter-current flow (oxygen concentration of water always higher than blood)

Fishes - Respiration “Warm-blooded” fish:  Epipelagic sharks, tunas, billfishes  Counter-current flow retains muscle heat  Body surface stays water temperature  Body core has elevated temperature

Fishes - Feeding Large mouth, tear chunks or swallow fish whole Small mouth, small prey Small mouth, small prey Hard beak, graze algae and coral Large mouth, filter feeder (plankton)

 Largest species:  Whale sharks (up to 60 ft)  Basking sharks (up to 50 ft)  Filter feeders (eat plankton) Whale (Rhincodon typus)Basking (Cetorhinus maximus) Fishes - Feeding

Fishes - Digestion

Fishes - Osmoregulation Equal solutes by adding urea Lower solutes, water loss

Fishes – Sensory Organs  Vision  Taste buds  Smell – olfactory sacs, nostrils  Sound – inner ear, otoliths (bones)

Fishes – Sensory Organs  Vibrations – lateral line (for hearing, too)

Fishes – Sensory Organs  Electroreception – ampullae of Lorenzini (cartilaginous fishes only) small holes

Fishes – Schooling  Use senses to coordinate (vision, sound, lateral line)  Protection from predation  Safety in numbers  Visual confusion  Feeding  Mating  Swimming efficiency

Fishes – Reproduction  Fertilization  External – bony fishes  Internal – cartilaginous

Fishes – Reproduction  Development  Oviparous (most bony fishes, some cartilaginous):  External eggs, yolk

Fishes – Reproduction  Development  Ovoviviparous:  Internal eggs, yolk, live-birth  Viviparous:  Internal eggs, nutrition from mother, live-birth

Fishes – Reproduction  Asexual – parthenogenesis (“virgin births”)  Very rare  Female sharks in captivity  Female offspring (genetic clones) Bonnethead – 2001Black-tip – 2008

Fishes – Reproduction  Strategies  Many small eggs (tarpon – 100 million eggs each spawn)  Fewer large eggs (more work)

 Planktonic fish larvae Fishes – Development

 Coastal fish use estuaries as nurseries Fishes – Development

Cartilaginous vs. Bony Fishes CartilaginousBony Scalesplacoidcycloid, ctenoid Mouthventralterminal Tail lobesunequal (heterocercal)equal (homocercal) Gills5-7 pairs, slits4 pairs, covers Position in waterfins, lower density (cartilage and oily liver) swim bladder Osmoregulationurea (equal solutes), rectal gland less solutes, gill excretion Sensoryampullae of Lorenzini, lateral line lateral line Reproduction (fertilization, development, strategy) internal, variety, fewer offspring external, mostly ovipary more offspring