The Bony Fishes Class Osteichthyes

Class Osteichthyes – The Bony Fish• More than 27,000 species• Most numerous and successful of all

vertebrates• Found in every marine habitat

– tide pools to deep sea

• Economically important– 77 million tons harvested per year

General Characteristics

• Endoskeleton made of true bone• Hinged jaws• Paired fins – independently movable

Types of Bony Fishes• Lobe-finned Fish:

– Ancestors of amphibians– Ex: coelacanth – thought extinct 65 million years

ago – found live in 1938 – 2 species– Ex: lungfish – lung that can breathe air during

droughts

• *Ray-finned:– Most present day fish

Movement• Nektonic – swimmers - control

movement against current–Move to food–Escape predator

Movement• Streamlining to reduce drag = teardrop shape =

fusiform• Most fish swim by moving tail side to side• Mucus reduces drag• Homocercal tail – top and

bottom same size

yellowfin tuna

Buoyancy• Gas-filled swim bladder – to maintain position

in water• Control quantity of gas• Not present in fast moving fish or sharks

Gas Exchange• Gills covered by operculum• Water pumped through mouth, over gills, out

gill slits and operculum• Thin membranes and high surface area in gills• Oxygen diffuses from water into blood• Carbon dioxide diffuses from blood to water

striped bass

Osmoregulation• Maintenance of water balance• Saltwater fish tend to lose water• Drink seawater• Excrete salt from gland in gills• Produce little urine

Osmoregulation

Senses• To find prey and avoid being eaten• Good sense of sight, smell and taste• Good sense of hearing – inner ear• Lateral line system:

– Line of pores and canals running down body– Detect vibrations, changes in current direction

and water pressure

Outer Covering

• Mucus – reduces friction and prevents infection

• Scales – protective outer cover– Overlap like roof shingles– Can tell age of fish

Outer Covering

Reproduction• Separate sexes• External fertilization = spawning

–Female releases eggs–Male releases sperm on top

Protection

• Camouflageex: flounder, sea dragon,

sargassum fish

Protection• Armor platingex: seahorses• Sizeex: puffer fish• Spinesex: blow fish

Protection

• Countershading - dark on top, light colored on bottom

• Disappear, ex: flying fish – leaps out of water• Deceptive markings, ex: butterfly fish

Protection• Schooling– ¼ of all species at some point in life– Looks like one large individual– Confuses predator– Hard to catch one fish– Easier feeding– Easier mating

Other Fish Adaptations

• Angler fish – lure to attract prey• Deep sea fish – bioluminescence

Fish Oddities

• Some start life as male, change to female or opposite – ex: some grouper, sea bass, sheepheads, wrasses

• Ocean sunfish – Mola mola - planktonic