Osteichthyes

The Bony Fish

Class Osteichthyes

Characterized by having:• Bone in their skeleton • An operculum covering the gill openings• A swimbladder or lungs• True scales• Paired fins• Homocercal tail (Exception lungfish –

diphycercal)• Mouth terminal• Two chambered heart• Sexes separate (Sex reversal in some)• Fertilization external for most• Excrete ammonia

Class Osteichthyes

The bony fishes are the most diverse class of fish. ~24,000 species

Osteichthyes are divided into two subclasses

• The lobe-finned fish (Sarcopterygians) • The ray-finned fish (Actinopterygians).*Most modern fish are members of the ray-

finned, Teleost subdivision.

Sarcopterygians

• Sarcopterygians are the fish most closely related to modern amphibians, reptiles, birds, and mammals

• This subclass includes the lungfish and coelacanth. Coelacanth were thought to have become extinct at about the same time as the dinosaurs, until a live specimen was found in 1938

Sarcopterygians

• Characteristics:• Muscular lobe associated with fins• Have lungs for gas exchange• Live in areas with seasonal droughts• Can breathe air if water stagnates• Cannot withstand desiccation• Burrow in the mud • Have enamel on the teeth

Sarcopterygians

• Can survive drought by remaining in aestivation for 6 months or more

• Aestivation = dormant state

• After rain fills the lake or riverbed Lungfish emerge from their burrows to feed & reproduce

Lungfish - Found in Australia & Madagascar

Lungfish scales

• Cosmoid scales

Lungfish Circulation

Coelacanth

                                                   

         

Actinopterygians

• Ray-finned fish (Fins lack muscular lobes)

• Have swimbldders to regulate buoyancy

• ~23,900 species

Chondrosteans (Fresh water fish)

• Include stergeons and paddlefish• Stergeon eggs make caviar

Caviar = Sturgeon eggs

Paddlefish

Subdivisions of Teleostei

• Superorder Ostariophysi• Order Cypriniformes (minnows, carps)• Order Siluriformes (catfish)• Superorder Protacanthopterygii• Order Esociformes (pikes)• Order Osmeriformes (smelts)• Order Salmoniformes (salmon, trout, whitefish)• Superorder Paracanthopterygii• Order Gadiformes (cod, hakes, pollock)• Superorder Acanthopterygii• Order Percoidei (perches, snook, basses)• Order Pleuronectiformes (flounders, soles)• Order Perciformes (mackerel, tuna, swordfish)

Actinopterygians The Teleosts

• Teleosts are modern day ray-finned fish• Use their fins and body wall to push

against water for locomotion• Some secrete mucus to reduce friction• Most teleosts are carnivores swallowing

prey whole• Herring & paddlefish are filter feeders• Teleosts have pyloric ceca (outpockets

in the small intestine to increase absorption)

Ganoid Fish Scales

• Found on non-teleost bony fishes

• Usually diamond shaped bony scales

• “Heavy armor”

Cycloid Fish scales

• Found on teleost fishes

• Light, thin, & flexible

Ctenoid Fish Scales

• Teleost fishes• Have comblike

ridges along the exposed edge to reduce friction (drag)

Myomeres

Swimming mechanics

• Thrust- force in animal's direction 

• Lift- force opposite in right angles to the thrust 

• Drag- force opposite the direction of movement

Swimming mechanics

• Yaw – side to side movement of head

• Pitch – up and down movement of head