Fishes

1. Fishes Chapter 24

2. I. Diversity • 26,000 living species—more species than all other vertebrate groups combined • Adapted to live in a medium 800 x more dense than air • Can adjust to salt and water balance of environment • Gills extract oxygen from water that has 1/20th the oxygen of air • Aquatic environment both shaped and constrained their evolution

3. II. Ancestry and Evolution • A. Ancestor • Descended from free-swimming protochordate ancestor • B. Agnathans • Earliest fish-like vertebrates • Include extinct ostracoderms, and living lampreys and hagfishes • C. Placoderms • Fish with paired appendages and jaws that went extinct in Carboniferous with no living descendants

4. D. & E. • D. Cartilaginous Fishes • Lost heavy armor and adopted cartilage as skeleton • Flourished during some periods, becoming nearly extinct during others • E. Acanthodians • Resemble bony fish but have heavy spines on all but caudal fin; sister group to bony fishes • Went extinct in lower Permian

5. F. Bony Fishes • Dominant fishes today • 2 distinct lineages—ray finned and lobe finned • Ray-finned radiated to form modern bony fishes • Lobe-finned include lungfishes, the coelacanth, and are sister group to tetrapods (amphibian ancestors)

6. III. Superclass Agnatha: Jawless Fishes • A. Characteristics • Lack jaws, internal ossification, scales, or paired limbs • Pore-like gill openings and eel-like body

7. B. Class Myxini: Hagfishes • 43 species • Entirely marine • Scavengers and predators of annelids, molluscs, dead or dying fishes, etc • Nearly blind but locates food by acute sense of smell • Rasps hole into prey then eats from inside out with plate-like tongue • Glands secrete substance that becomes slimy in contact with seawater

8. C. Class Cephalaspidomorphi • 1. Diversity • 41 species; 22 in North America and of these, half are non-parasitic brook variety • Marine lampreys can grow to length of 1 m. • All lampreys reproduce in freshwater streams, dying soon after

9. 2. Parasitic Lampreys • Attach to fish by sucker-like mouth and sharp teeth rasp away flesh • Anticoagulant injected into wound to stimulate flow of blood • Wound may be fatal to host fish • Non-parasitic lampreys do not feed; digestive system degenerates and fish die after reproducing, within 2-3 years

10. 3. Sea Lamprey Invasion • No lampreys existed in Great Lakes prior to 1829 when shipping canals were built • By the 1940’s, they existed in all the lakes • They decimated almost all fish species until populations finally declined due to lack of food and control measures

11. IV. Class Chondrichthyes • A. Overview • 850 species nearly all marine; 28 species live in freshwater • Ancient lineage but have survived due to well-developed sense organs and powerful jaws making them successful predators • Largest living vertebrates, after whales, reaching up to 12 m in length Whale shark reaches 43’ in length

12. B. Subclass Elasmobranchii • 1. Sharks • A. Orders • Carcharhiniformes—tiger and bull sharks which are coastal sharks and the hammerhead • Lamniformes-- white and mako sharks which are large pelagic sharks • Squaliformes—some of these are deep sea dwellers like dogfish sharks • Orectolobiformes—carpet sharks like bamboo, nurse, and whale sharks

13. Sharks

14. More Sharks

15. b. Outer Physiology • Streamlined fusiform body shape • Pointed nose with paired nostrils in front of ventral mouth; on hammerhead, nostrils on ends of “hammer” • Lateral eyes without lids • Tail has longer upper lobe (heterocercal) • Paired pectoral and pelvic fins, 1-2 dorsal fins, 1 caudal fin, and sometimes an anal fin • Tough, leathery skin with placoid scales that reduce water turbulence

16. Body Structures of a Shark

17. c. Senses • Olfactory organs can detect chemicals diluted 1/10 billionth their original concentration • Lateral line senses low frequency vibrations of prey over large distances • Excellent vision, even in dim water, used at close range • At close range, sharks are guided to prey by electric fields surrounding all animals

18. d. Inner Physiology • Sharp triangular teeth in upper and lower jaws; arranged in rows that are constantly replaced • Mouth leads to pharynx with openings to gill slits • Osmoregulation accomplished by rectal gland which secretes sodium chloride; nitrogenous compounds are also retained in blood to increase solute concentrations, making more on par with seawater

19. e. Shark Attacks • Only 32 species ( of 350) have been documented to attack humans with another 36 considered potentially dangerous; these typically are the larger size sharks; 80 % of sharks are harmless • Great white, tiger, and bull sharks are the more aggressive species • 50-75 attacks occur each year, with 8-12 fatalities; in contrast 30-100 million sharks are killed every year • Attacks usually occur by sandbars, steep drop offs, or by river inlets and are associated with mistaken identity,territorial behavior, or feeding behavior

20. 2. Rays • A. Order • Rajiformes—skates, sawfish rays, electric rays, stingrays, manta rays and others • Make up half of all species of Elasmobranchii

21. b. Form and Function • Specialized for benthic life • Flattened dorsoventrally; enlarged pectoral fins are used as swimming wings • Water used in respiration enters large spiracles in head • Teeth adapted to act as rollers to crush invertebrates and sometimes small fish • Stingrays have whip-like tail with spines and venom glands • Electric rays have electric organs on sides of head

22. C. Subclass Holocephali: Chimeras • 31 species • Ratfishes • Diverged from earliest shark lineage • Mouth has flat plates for crushing invertebrates; also feeds on seaweed and small fish

23. Internal fertilization Oviparous sharks and rays lay an egg capsule immediately after fertilization that attaches to kelp with tendrils; may take up to 2 years before mini adult hatches Ovoviviparous sharks retain fertilized eggs in reproductive system where they are nourished by yolk of egg; “live” birth Viviparous sharks nourish embryos with maternal bloodstream; “live” birth Live births make it more likely more of the young survive but no other care is given after birth D. Reproduction and Development

24. Embryo Development

25. V. Superclass Osteichthyes • A. Origin, Evolution, and Diversity • Lineage developed in Silurian and now accounts for 96% of all fishes and all tetrapods • Bone replaces cartilage as fish develops • Lung or swim bladder evolved from an extension of the gut; gas filled, it aids in buoyancy • Bony operculum, a flap covering the gills that rotates outward, draws water more efficiently over them • Specialization of jaw musculature improves feeding; also unique dental characters

26. 23,600 species comprise the ray-finned fishes Most familiar fish type B. Class Actinopterygii

27. a. Palaeoniscids • Earliest forms, existing from late Silurian to late Paleozoic • Small, large eyes, dorsal fin with bony rays, heterocercal tail, and interlocking scales • Survived as other fishes declined, suggesting some adaptive advantage • Gave rise to the chondrosteons and the neopterygians

28. b. Chondrosteons • Most primitive characteristics • Heterocercal tail and ganoid scales • Living species include sturgeons, paddlefishes, and bichirs

29. c. Neopterygians • One lineage gave rise to modern bony fishes, the teleosts • Living species are bowfin and gars which gulp air and use vascularized swim bladder to supplement the gills

30. d. Teleosts • 96 % of all living fishes; half of all vertebrates • 10 mm to 17 m; up to 900 kg in weight • Found at 5,200 m to 8,000 m below sea level • Some can live in hot springs at 44 oC while others can survive in Antarctic –2 oC. • Some live in salt concentrations three times seawater; others in swamps devoid of oxygen

31. 2. Morphological Trends • Heavy armor replaced by light cycloid or ctenoid scales which made fish more mobile; some fish such as eels and catfish have completely lost scales • Fins changed to provide greater mobility and serve a variety of functions: braking, streamlining, and social communication • Homocercal tail allowed greater speed and buoyancy • Swim bladder switched from primarily respiratory to buoyancy in function • Jaw changed to increase suctioning and protrusion to secure food Cycloid Ctenoid

32. C. Class Sarcopterygii • 1. Diversity • Only 7 species alive today; 6 lungfishes and 1 coelacanth • Early ones had lungs as well as gills, heterocercal tail; later tail became symmetrical • Skin covered in heavy scales overlaid by an enamel • Fleshy, paired lobes are used to scuttle along bottom • South American and African lungfishes can survive out of water or long periods of time

33. 2. Coelacanth • Thought to have been extinct for 70 million years until one was dredged up off of coast of Africa in 1938 • More were caught off the coast of the Comoro Islands in 1998

34. VI. Structural and Function Adaptations • A. Locomotion • 1. Mechanism • Trunk and tail muscles propel fish forward by undulations • Large, rigid head minimizes yaw • Very rigid body creates less yaw and a fast fish • The largest fin is the tail or caudal fin for rapid forward movement. • Dorsal fins on the top and anal fins underneath assist with lateral stability. • Pectoral fins behind the gill covers (operculum) assist with hovering and slow turning. • Pelvic fins are often small for open water swimmers but larger on bottom dwellers which use them for resting on.

35. 2. Speed and Energy • Larger fish swim faster • Short bursts of speed are possible for a few seconds • Swimming is most economical means of motion since water buoys the animal; swimming expends 0.30 Kcal, 1.45 Kcal for walking, and 5.43 Kcal for flying

36. B. Swim Bladder • Fish are slightly heavier than water • A shark has a very fatty liver that makes it a little buoyant; must also keep swimming to move it forward and angle itself up • Bottom dwelling fishes also lack swim bladder • Fish can control depth by adjusting volume of gas in swim bladder • Gas gland removes or adds gases from blood to remove or add gas to bladder • Some fish gulp air to fill swim bladder

37. C. Respiration • Gill filaments are folds of tissue inside the pharyngeal cavity covered by the operculum • Continuous water flow opposite blood flow through capillaries maximizes gas exchange allowing some fish to remove 85% of O2 from H2O • Some fishes are dependent on ram ventilation as well, in which forward movement pushes more water over gills; such fish will die in an aquarium • Lungfish use lungs; eels use skin; bowfin uses gills at low temperatures and air bladder at higher temperatures; electric eel has degenerate gills and must gulp air

38. D. Osmotic Regulation • 1. Freshwater Fishes • Freshwater has less salt than blood of fish so water tends to enter fish’s cells and its salts tend to leave • Hyperosmotic regulators: kidney pumps out excess water and salt absorbing cells in skin remove salts from water and add to blood • Euryhaline fishes live in estuary environments where they are in contact with both fresh and salt water

39. 2. Marine Fishes • Blood has lower salt content than surrounding water so tend to lose water and gain salt • Hypo-osmotic regulators: fish drinks water bringing in more water but also salt; salt is carried by blood to gills where it is secreted by salt-secretory cells, some salt leaves in feces, and others are excreted by kidneys

40. E. Feeding Behavior • Most time devoted to searching for food and eating • Most carnivores-feed on zooplankton, insect larvae, and other aquatic animals • Most don’t chew food since it would block flow of water across gills; swallow food whole although a few have teeth that crack prey or have some molars in throat • Some herbivores--eat plants and algae • Suspension feeders eat plankton, using gill rakers to strain food; these fish swim in large schools • Also have omnivores, scavengers, and parasites • Stomach used for storage; intestines absorb and digest nutrients

41. F. Migration • 1. Eels • Catadromous—develop in freshwater but spawn in seawater • Adult eels spawn in Sargasso Sea at depths of 300 m. • Larvae drift for 2 years before developing into elvers; males remain in brackish water; females swim hundreds of miles up rivers • Females mature for 8-15 years before returning to the sea ( 8 months to complete journey) • American eels are separate species from European eels

42. 2. Salmon • Anadromous—living in sea but spawing in freshwater • 6 Pacific salmon species, and 1 Atlantic salmon species that migrate • Pacific species migrate downstream, live in Pacific for 4 years, and then return up the same stream it was spawned in • Young fish are imprinted with the odor of their stream • Pacific salmon spawn and then die • Endangered by stream degradation, logging, pollution, and hydroelectric dams

43. Reproduction • Most dioecious with external fertilization and development • Some are ovoviviparous where eggs develop in ovarian cavity—sharks, guppies, mollies • Oviparous marine fish lay large numbers of eggs, upwards of several million • Nearshore or bottom dwelling fish lay fewer, larger nonbuoyant sticky eggs • Some fish bury eggs, attach them to vegetation, incubate them in their mouths • Freshwater fish produce fewer, nonbuoyant eggs, and more care is usually provided • Many freshwater fish also have elaborate mating dances before spawning

44. H. Growth • Egg starts to take up water after it is laid, outer layer hardens, and cell division begins • Yolk is consumed during development • Fish fry hatch carrying semitransparent yolk sac to supply food until it can forage • As fry change to adult, it may undergo dramatic changes in body shape, fins, color patterns, etc • Growth is temperature dependent; warmer fish grow more rapidly • Annual rings on scales reflect seasonal growth cycles • Most fish continue to grow throughout life and do not stop at maturity

45. Fish Development