Class Osteichthyes

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