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

3. 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

4. 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!

5. 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

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

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

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

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

10. 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)

11. Those in the open water are less colorful.
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?

12. 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.

13. 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

14. 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…

15. 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.

16. 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

17. 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

18. 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