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Bony vs Cartilaginous Fish

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  1. Bony vs Cartilaginous Fish • Bony and cartilaginous fish differ not only in their gill and endoskeletal structure, but also in their response to meeting the challenges of an aquatic existence

  2. Why water aerobics are a great workout • Water is ~800 times denser than air, and 100 times more viscous • Impedes moving effectively at low speeds • Nekton have evolved special adaptations to efficiently move through the water column

  3. The dynamics of swimming • To avoid sinking out of surface waters, fishes must increase their buoyancy or swim continually • Cartilaginous fish store various lipids in their liver and tissues, which are less dense than the surrounding seawater • Their cartilaginous skeletons are ~one half as dense as the skeletons of bony fishes

  4. The dynamics of swimming • Most pelagic bonyfish have air bladders to compensate for the relative heavy bony skeleton • Air bladders, or swim bladders are gas-filled floats which provide more buoyancy than the storage of body lipids • Found in pelagic, not benthic,fish • Why?

  5. Air bladder • One major disadvantage: gas responds to changes in pressure by expanding and contracting • Modern fishes have a series of blood vessels and capillaries connected to the swim bladder which fill (and remove) air to control their buoyancy

  6. Can someone give me a lift? • Another way to avoid sinking out of the pelagic zone is to employ dynamic lift • Sharks generate lift by their large, stiffened pectoral fins • Bernoulli’s principle: An increase in speed causes a decrease in pressure; water travels faster over the top of the fin creating a region of low pressure (lift)

  7. How airplanes (and sharks) fly • Thrust is generated by engine • Lift provided by wing of the airplane • Air traveling over the wing is deflected upwards over the top surface and downwards beneath the lower surface; but because of the shape of the wing, air is deflected differently such that pressure is lower above the wing (air travels faster), generating lift

  8. Sharks are really, really fly • The shape of a shark’s pectoral fins and their position relative to their body generates upward lift in the same way that planes do! • Requires constant forward motion (need thrust to generate lift)!

  9. Just keep swimming, just keep swimming • Pelagic fishes usually have stream-lined shapes that make their propulsive efforts more effective • Reduces drag • torpedo shape most effective Mahi mahi (dolphinfish)

  10. Body shape • The body shape of a fish is directly related to its lifestyle • Fast swimmers like sharks and tuna have a streamlined body that help them slice through the water • Body shape can be especially useful for camouflage • An irregular shape can be an excellent means of concealment

  11. Can you find the pygmy sea horse?

  12. Finding Nemo…

  13. Just keep swimming, just keep swimming • Fishes must swim to obtain food, find mates, and escape from predators • Most fish swim with a rhythmic side to side motion of the body or tail, produced by bands of muscles called myomeres • Make up to 75% of weight in active fishes

  14. Just keep swimming, just keep swimming • Paired fins combined with a tail and a relatively inflexible body propel fish through the water

  15. Swim class • Bony fish use their pectoral fins, not for lift, but rather maneuverability • They can brake, hover, and change position • The dorsal and anal fins act as rudders, and provide stability

  16. Respiratory system of fishes • Fish obtain oxygen using paired gills • Gills are specialized extensions of tissue that ‘project’ into the water • Large surface area • High blood flow • Works by way of a counter- current exchange system

  17. Gills maximize gas diffusion • Gas exchange involves diffusion across membranes • The external environment must always be aqueous • Diffusion is passive; driven by the difference in O2 and CO2 on the two sides of the membrane • The rate of diffusion is governed by Fick’s law of diffusion

  18. D A Dp Rate of diffusion = d Fick’s Law of Diffusion D = diffusion constant (molecule specific) A = area over which diffusion occurs Dp = pressure difference between two sides d = distance over which diffusion occurs Maximized by increasing surface area, increasing the concentration difference, and decreasing the distance over which diffusion occurs

  19. Gills maximize gas diffusion Gills maximize gas exchange by consisting of many rows of thin plates or lamellae which increase surface area ( A) and contain capillaries ( d), along which counter-current gas exchange occurs H20 ( p) Rate of diffusion = D A Dp d

  20. Countercurrent gas exchange


  22. Gas exchange in fishes • Bony fish have four gill arches on each side of their heads • Each gill arch is composed of two rows of gill filaments, which consist of lamellae

  23. Gas exchange in fishes • In contrast, cartilaginous fish have 5-7 pairs of gills • The first pair of gill slits is modified into a pair of spiracles

  24. Gas exchange in fishes • Mobile fish (cartilaginous fishes and tunas, etc.) swim with their mouth open to continuously move water passed the gills; this is known as ram ventilation

  25. Gas exchange in fishes • Most bony fish use pumping action (not ram) to ventilate; but many alternate between ram and pumping to move water across their gills

  26. Gas exchange in fishes • Benthic sharks, skates, and rays pump water through their spiracles • Moves water over the gills while resting on the mouth • Important for rays and skates when buried

  27. White meat or dark? • Hemoglobin in the blood carries oxygen through the fishes body; Muscles also contain myoglobin which can also store oxygen • Strong swimmers have a higher proportion of myoglobin and thus a higher proportion of red muscle, as opposed to white, which is used for short bursts of speed

  28. The return of endothermy!!! • Some fish are “warm-blooded” in that they can increase the internal temperature of their body to one higher than the external environment • Counter-current heat exchange system • Body surface remains at water temperature; body core is elevated

  29. Something smells fishy • Most fishes have a highly developed sense of smell which is used to detect food, mates, predators and sometimes to find their way home • Salmon memorize the sequence of smells on their way out to sea, so they may return to spawn • Sense of smell is particularly well-developed in the sharks • Can detect a drop of blood in concentrations less than one part per million

  30. Sensory organs of fishes • Fishes have a unique sense organ called the lateral line that enables them to detect vibrations in the water • The lateral line consists of a system of small canals that run along the head and body • Lined with sensory cells, or neuromasts that are sensitive to vibration via clusters of hair • Allows fishes to avoid collisions and predators, detect prey, orient to currents, and maintain position in a school

  31. Lateral Line of Fishes

  32. Sensory organs of fishes • In addition to a lateral line, cartilaginous fish have sensory organs in the head known as ampullae of Lorenzini that can detect weak electrical fields • Helps locate prey, may also aid in navigation

  33. You’re about to get schooled • Many fish form well-defined groups, or schools • Some, including herring, sardines, and some mackerels school throughout their lives • Schools function as well-organized units, with no known leader • The individual fish tend to keep a constant distance between themselves; turning, stopping and starting in near perfect unison

  34. You just got schooled • Fish use vision, lateral line, scent and sound to keep track of one another and maintain unity • Protection against predators (safety in numbers) • Also aids in feeding, swimming, and finding mates

  35. Reproduction and Life History • The sexes are usually separate in fishes, although a few marine fishes are hermaphroditic (both male and female) • Some hermaphrodites are simulataneous, simultaneously being both male and female, while others are sequential, beginning life as a male (or female) and changing into a female (or male)

  36. Reproduction and Life History • Sex reversal occurs in several groups of marine fishes, but it is prevalent among sea basses and groupers, parrotfish, and wrasses • Makes the most sense to begin as male and become female; why?

  37. Finding (the truth about) Nemo • Some species of anemone fish begin life as males; each anemone is inhabited by a single, large female that mates only with a large, dominant male • All the other fishes on the anemone are small, non-breeding males; when the female dies, her mate changes into a female and the largest of the non-breeding males becomes the new dominant male

  38. Reproduction and Life History • Most fish reproduce via external fertilization where eggs and sperm are released, or broadcast into the water • Internal fertilization occurs mainly in cartilaginous fishes via male copulatory organs called claspers

  39. There’s always a bigger fish…