Class Osteichthyes
“Bony Fish”
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Class Osteichthyes
General Characteristics
• The largest (by species) class of vertebrates– Over 29,000 known species
• Bony skeleton of calcium
• Dermal scales provide protection, but are very different from chondrichthyes scales – Epidermal mucous secretion=reduce friction
• Bilateral symmetry– Appendages adapted for aquatic environment
General Characteristics
• Aquatic respiration– Paired gills
• Gills covered by operculum (allows fish to breathe without swimming)
• Habitat – salt, fresh, warm, cool – anywhere!!
General Characteristics
• Swim bladder – – Creates neutral buoyancy– Can also act as resonating chamber
for hearing
• Mouth/jaw well developed– Fine teeth
Scales
• 3 types of scales– Ganoid
• Very tough, external coating of protective enamel
• Diamond shape, shiny
• Uncommon in modern fish (found on sturgeon, gar)
Scales
–Ctenoid• Terminate in tiny
spines along posterior edge
• Most common type of scale in bony fish
Scales
–Cycloid• Smooth
• Overlap for flexibility
• Grow in concentric rings each winter – “age rings”
Skeleton
• Endoskeleton – axial & appendicular– Axial – pertaining to the central axis of
the body – skull, vertebrae, ribs, spines, caudal vertebrae
– Appendicular – parts of the skeleton adjacent to the axial skeleton – pectoral girdle, pelvic girdle, fin rays
Muscular
• Segmented muscles (myomeres) – overlapping, segmented muscles in a zig-zag shape, used for swimming and undulating tail movement
Digestive
• Complete – mouth, pharynx, esophagus, stomach, pyloric valve, pyloric caeca, intestines, anus– Also have liver & gall bladder to aid in
digestion
Circulatory
• Closed – two chambered heart – Pericardial cavity with an auricle & a ventricle– Arteries lead away from heart to gills – veins
return blood to the heart– Capillaries close the system between arteries
& veins at the cells
Respiratory
• Aquatic – gills– Gills covered by muscular plate – “operculum”– Gill filaments – minute capillaries for
absorption of O2 & excretion of Co2– Gill arch – provides cartilaginous support– Gill rakers – protect against foreign substance
entering gills (cleaning & filtering water)
Excretory
• Two kidneys – strains fluid nitrogenous waste– Ureter – Fluid tube leading to urinary bladder
Nervous system/sensory• Brain well developed – division of function
• Nerve cord branches to lateral spinal nerves– Cerebral hemisphere – capable of “thinking”
– Olfactory lobes – receive & process signals from nostrils• Nostrils – olfactory sacs pick up dissolved
substances (aquatic smelling)
– Auditory – inner ear• Otolith – bone growth for equilibrium & balance
Nervous system/sensory
– Lateral line – picks up low frequency vibrations – aquatic touch/hearing
– Optic lobes – midbrain area, process vision• Eyes – well developed, binocular – allow fish
to be predaceous• See in color; some can see ultraviolet light
– Taste buds – fish have taste preferences, can distinguish what’s “good”
Reproduction
• External fertilization (oviparous) – most species– Brook trout – 80 eggs– Ocean sunfish – 5,000,000
• A few species are viviparous
