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