Class Osteichthyes

Class Osteichthyes “Bony Fish”

Class Osteichthyes Subphylum Vertebrata Phylum Chordata Kingdom Animalia

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

Class Osteichthyes