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Fish Notes Part 3

Fish Notes Part 3. Skin, scales, color, defense, migration and reproduction. Skin. Entire skin of fish is alive (unlike vertebrates) Covered in scales – grow from pockets in skin Not covered by a layer of dead skin, hair or feathers Covered by water at all times

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Fish Notes Part 3

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  1. Fish Notes Part 3 Skin, scales, color, defense,migration and reproduction

  2. Skin • Entire skin of fish is alive (unlike vertebrates) • Covered in scales – grow from pockets in skin • Not covered by a layer of dead skin, hair or feathers • Covered by water at all times • Scales covered by a thin layer of living cells  epidermis

  3. Protection is provided by a thin covering of mucus which reduces friction and lessens the possibility of bacteria and parasites from invading the skin • “fish” odor – found in slimy covering – serves as a means of communication • Scales can also help the fish “taste” the water—some fish have taste buds on their scales & fins!

  4. Scales • Have about the same # for life – count rings on them for growth (although can be tricky…) • Fish w/o scales  lampreys, freshwater catfish • Eels appear “scaleless” but actually have small scales deeply embedded in the skin

  5. Scales (con’t) • Placoid Scales • Tooth-like • like sandpaper • Ex. sharks and skates

  6. Ganoid Scales • Large and plate-like – made of bone • Generally fused to form a hard bony covering • Ex. primitive fish, gar, sturgeon

  7. Scales (con’t) • Cycloid scales • Overlapping covering like shingles • Thin/flexible • Smooth • Found in soft-rayed bony fish • Ex. salmon

  8. Ctenoid scales • Overlapping like cycloid but rough • Comb-like edge • Spiny-rayed bone fish  mackerel

  9. Coloration • Fish show a variety of colors with a variety of functions: • Species recognition during breeding • Camouflage • Warning/poisonous • Advertisement for willingness to remove parasites from other fish (remora)

  10. Two types of cells are located in fish skin: • Chromatophores – star shaped pigment cells – fish can change colors by contracting or expanding these • Iridocytes – contain reflecting granules that work like small mirrors Those in the open water are less colorful. Why?

  11. Defensive strategy • Other than feeding • Modified scales  sharp spines, armor, camouflage • Prehensile tails (sea horse) • Sudden expansion (puffer fish) • Coloration • Countershading – dorsal area is darker than ventral • Disruptive contrast – violently contrasting coloration – ex. stripes, etc.

  12. Defensive strategy • Secretions (ink/poisons) • Schooling – safety in numbers – some part time and some do this their whole life • Intimidating behavior = bluffing, raised fins, open mouth, rapid darting, grinding teeth, rubbing spines

  13. Migrations • 2 underlying needs are directing seasonal migrations and they are: • Locating a suitable place to breed • Seeking food • Migratory fish are grouped according to the type of water in which they breed…

  14. Anadromous • Adult life in ocean – return to fresh water to breed – ex. salmon, sturgeon, shad, smelt, sea lamprey **Salmon live several years in the sea and mature sexually then return to rivers. They don’t feed once in freshwater – rely on stored fat. Eventually they reach the exact stream where they were born. Females dig a shallow next where she lays her eggs. The males fertilize and then both die. How do they find the exact place? They use chemical smells as a homing technique.

  15. Catadromous • Adult life in freshwater – return to sea to breed • Ex. eel Some fish remain in the ocean and move on definite pathways b/n feeding areas and spawning areas – ex. herring and tuna

  16. Reproduction • Fish reproduce sexually in many ways • Most do it externally (females release eggs, males release sperm – millions of eggs – called spawning) – sharks are internal • Terms to know: • Milt – fish sperm produced in testes • Roe – fish eggs produced in ovaries • Some are dioecious (most) but some hermaphroditic (they are able to produce sperm and egg in combination – have ovotestes – ex. lancelfish, tripod fish, top minnow (may self-fertilize) • sex reversal – a means to improve reproductive success – maintains an even number of males and females – ex. grouper, sheepshead, and wrasse

  17. Reproduction • For some the urge to breed in controlled by hormones  timing is controlled by: • Temperature • Day light length • Salinity • Tide cycles • Courtship rituals (provide for species identification) • Bright color display • Nest building • Aggression • “dances” • Specific sounds

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