1. The Fishes: Vertebrate Success in Water
Chapter 18
The Fishes: Vertebrate Success in Water

2. Evolutionary Perspective
Phylogenetic Relationships
Subphylum Craniata
Skull surrounds brain, olfactory organs, eyes, and inner ear.
Infraphylum Hyperotreti
Infraphylum Vertebrata
Fossils record
Craniates and bone date earlier than 500 mya.

3. Survey of Fishes Infraphylum Hyperotreti—Class Myxini Hagfishes
Head supported by cartilaginous bars.
Lack vertebrae and retain notochord
4 pairs of sensory tentacles around mouth
Ventrolateral slime glands
Marine
Scavenge dead and dying fish

4. Figure Class Myxini.

5. Survey of Fishes Infraphylum Vertebrata Vertebrae surround nerve cord.
Figure An ancient Silurian seafloor with two ostracoderms (Pteraspis and Anglaspis).
Infraphylum Vertebrata
Vertebrae surround nerve cord.
Ostracoderms
Extinct agnathans
Bony armor
Bottom dwellers

6. Survey of Fishes Class Petromyzontida Marine and freshwater
Most are predators as adults, filter-feeders as larvae
Brook lampreys
Adults do not feed.
Life cycles involve open water adult stages and stream or river larval stages (figure 18.7).

7. Figure 18.6 Class Petromyzontida (Petromyzon marinus).

8. Figure 18.7 Life history of a sea lamprey.

9. Survey of Fishes Superclass Gnathostomata
Jaws developed from anterior pharyngeal arches.
Paired appendages
Classes
Chondrichthyes
Actinopterygii
Sarcopterygii
Figure Paired pectoral and pelvic appendages of a member of the Gnathostomata.

10. Survey of Fishes Class Chondrichthyes
Placoid scales, cartilaginous skeleton
Subclass Elasmobranchii
Sharks, skates, rays
Subclass Holocephali
Ratfish
Operculum present

11. Figure 18.9 Class Chondrichthyes. (a and b) Subclass Elasmobranchii.
(a) Reef shark (Carcharhinus perezi). (b) A bullseye stingray (Urolophus concentricus).
(c) Subclass Holocephali. The ratfish (Hydrolagus colliei).
(b)
(a)
(c)

12. Figure 18.10 Scales and teeth of sharks.
(b)

13. Survey of Fishes Class Sarcopterygii Lobe-finned fishes
Fins with muscular lobes
Lungs used in gas exchange.
Lungfish
3 genera
Australia, Africa, South America
Coelacanths
2 species
African and Indonesian coasts
Tetrapodomorpha
Extinct ancestors of ancient amphibians and all tetrapods

14. Figure 18.11 Class Sarcopterygii. The lungfish, Lepidosiren paradoxa.
Figure Class Sarcopterygii. The coelacanth Latimeria.

15. Survey of Fishes Class Actinopterygii Ray-finned fishes Swim bladders
Fins lack muscular lobes
Swim bladders
Chondrosteans
Sturgeons and paddlefish
Neopterygii
Garpike (Lepisosteus) and dogfish or bowfin (Amia)
Modern bony fish—the teleosts

16. Figure 18.13 Class Actinopterygii, the chondrosteans.
(a) Shovelnose sturgeon (Scaphirhynchus platorynchus).
(b) Paddlefish (Polydon spathula).

17. Figure 18.14 Class Actinopterygii, the teleosts.
(a) A flounder (Pseudopleuronectes americanus).
(b) Yellowtail snappers (Ocyurus chrysurus).

18. Evolutionary Pressures
Locomotion
Streamlined shape, mucoid secretions, buoyancy of water, body-wall muscles, fin shape all promote efficient locomotion.
Nutrition and the digestive system
Filter feeders and scavengers
Modern filterers use gill rakers.
Predators (most modern fish)
Swallow food whole
External parasites (lampreys)
Herbivores
Digestive tract
Specializations include spiral valve (sharks) and pyloric cecae (bony fishes).

19. Evolutionary Pressures
Circulation
Closed
Heart
4 embryological enlargements of ventral aorta
Sinus venosus
Ventricle
Atrium
Conus arteriosus
Most fish have single circuit.
Lungfish
Pulmonary circulation
Pulmonary and systemic circuits

20. Figure 18.15 Circulatory system of fishes.

21. Evolutionary Pressures
Gas exchange
Water movement over gills
Opercular and pharyngeal muscles pump water in most fishes.
Ram ventilation in elasmobranchs and open-ocean bony fish
Gas exchange surfaces
Visceral arches support gills.
Gill filaments and pharyngeal lamellae
Countercurrent exchange mechanism
(figure 18.16)

22. Figure 18.16 Gas exchange at pharyngeal lamellae.
(a) Gill arches. (b) Trout lamellae. (c and d) Comparison of countercurrent and parallel current exchanges.

23. Evolutionary Pressures
Swim bladders and lungs
Pneumatic sacs connect to digestive tract in nonteleost fish.
Function as lungs in lung fish, climbing perch and ancient rhipidistians
Function as swim bladders in other bony fish
Buoyancy Regulation
Low density compounds
Fins provide lift.
Reduction of heavy tissues
Swim bladders
Pneumatic duct (gulp air)
Counter current exchange at rete mirabile

24. Figure 18. 17 Possible sequence in the evolution of pneumatic sacs
Figure Possible sequence in the evolution of pneumatic sacs. (a) Origin as ventral outgrowths of esophagus.
(b) Primitive lungs. (c) Swim bladders move dorsal in position and lose connection to gut tract.

25. Evolutionary Pressures
Nervous and sensory functions
Brain and spinal cord
Sensory receptors
External nares
Eyes
Lidless and round lens
Inner ears
Equilibrium, balance, and hearing
Lateral line system
Sensory pits in skin detect water movements.
Electroreception
Prey detection by chondrichthyians
Gymnarchus (figure 18.18)
Electrophorus (electric eel)

26. Figure 18.18 Electric fishes.
(a) Electrical fields are used to detect the presence of prey and other objects in a murky environment. (b) The electric fish (Gymnarchus niloticus).

27. Evolutionary Pressures
Excretion and Osmoregulation
Kidneys
Filter nitrogenous wastes, ions, water, and small organic compounds at nephrons
Glomerulus is filtering capillary network.
Tubule system promotes reabsorption.
Freshwater fishes
Excess water must be excreted.
Ions and organic compounds are selectively reabsorbed.
Marine fishes
Water must be conserved.
Excess ions excreted.

28. Evolutionary Pressures
Excretion and Osmoregulation
Elasmobranchs
Sequester urea in body tissues
Rectal gland
Diadromous fishes
Gills cope with both uptake and excretion of ions.
Nitrogen wastes
90% ammonia (diffusion across gill surfaces)
10 % urea, creatine or creatinine (kidneys)

29. Evolutionary Pressures
Reproduction and development
Most oviparous
Some ovoviviparous (some elasmobranchs) or viviparous (other elasmobranchs)
Fertilization
Most external
Copulatory structures
Claspers in elasmobranch males
Development
Usually little or no parental care
Some tend nests or brood young

30. Figure The male garibaldi (Hypsypops rubicundus) cultivates a nest of red algae, entices a female to lay eggs in the nest, and defends the nest.

31. Further Phylogenetic Considerations
Two series of evolutionary events
Radiation of teleost fishes
Evolution of terrestrialism
Terrestrialism
Tetrapodomorpha
Osteolepiform sarcopterygians
Common features with amphibians
Jaws, teeth, vertebrae, limbs
Tiktaalik (the “fishapod”)
Fins, gills, scales
Dorsoventrally compressed and widened skull
Tetrapod-like forelimbs
Lacked opercular supports and dorsal and anal fins
Pectoral girdle and freely moveable neck

32. Figure 18. 22 The fishapod Tiktaalik
Figure The fishapod Tiktaalik. This 375-million-year-old fossil helps us understand the transition between sarcopterygian fish and tetrapods. Its tetrapod-like features were probably used in foraging the water’s edge for prey.

33. Box Figure The fossil record provides clear evidence of the evolution of the tetrapod limb. (a) The sarcopterygian Eusthenopteron.
(b) The sarcopterygian Sauripterus. (c) The forelimb of the tetrapod Acanthostega. (d) The hindlimb of the tetrapod Ichthyostega.