Skin, scales, color, defense, migration and reproduction 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 Scales covered by a thin layer of living cells  epidermis

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!

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

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

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

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

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

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)

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?

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.

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

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…

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.

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

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

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