Fishes and Amphibians

 Classified in the phylum Chordata  Subphylum vertebrata ◦ Have a back bone ◦ Bilateral symmetry ◦ Coelomate ◦ Have endoskeleton ◦ Closed circulatory system ◦ Nervous system with complex brain ◦ Efficient respiratory system

 Three classes of fish in the subphylum vertebrata ◦ Agnatha- jawless fish  Lampreys, hagfishes ◦ Chondrichthyes- cartilaginous fishes  Sharks and rays ◦ Osteichthyes- bony fish  Perch, bass, etc.

 Over 20,000 species of fishes exist ◦ More than all the other vertebrates put together  Fish use gills for respiration ◦ Water flows over gills for gas exchange  Fish have a two-chambered heart ◦ One chamber receives deoxygenated blood ◦ The other chamber pumps blood to capillaries and gills where oxygen is picked up ◦ Blood flows slow because most of pumping action is used to move blood to gills

 Fishes reproduce sexually ◦ Have different sexes ◦ Fertilization is external in most fishes ◦ Most produce large numbers of eggs ◦ Some Chondrichthyes have internal fertilization ◦ Reproduction in fish is called spawning ◦ Number of eggs is related to parental care of young

 Most have paired fins ◦ Only members of Osteichthyes and Chondrichthyes ◦ Fins are fan shaped membranes used for balance, swimming and steering ◦ They foreshadowed the limbs used by land animals

 Senses ◦ Fish have a lateral line system  Fluid filled canal that allows them to feel vibrations and movement in the water ◦ some fish have extremely sensitive smell  Sharks- detect small amounts of blood in water  Most fish have scales ◦ Bony plates formed from the skin ◦ Can be used to age fish ◦ Agnatha don’t have scales

 Have a developed jaw ◦ One of the most important developments in ancient fish ◦ Allows for grasping and crushing of prey ◦ May account for large size of ancient fish ◦ Class Agnatha doesn’t have jaws…  Most fish have a bony skeleton ◦ Only class Osteichthyes ◦ Allowed fish to adapt to many environments and eventually to life on land

 Bony fish have separate vertebrae ◦ Allows for support and better movement and flexibility  Bony fish evolved swim bladders ◦ Acts like a blimp and allows fish to control what depth in the water they are at ◦ Some fish like African lung fish, can gulp air into a modified swim bladder connected to the mouth.

 Range in size from less than 1cm to 15m!  Agnathans are jawless ◦ Drill a hole in their prey and suck out blood and insides from animals ◦ Skeletons made of cartilage  Sharks and rays are made of cartilage ◦ Have not changed much in 100,000 years  Are called “Living fossils” ◦ Some rays have sharp spines with poison for protection. Other species can produce electricity!

 Scientists recognize three subclasses of bony fish ◦ Lung-fishes  Have both gills and lungs ◦ Lobe-finned fishes  Represented by only one species that was thought to be extinct  Coelacanth  Ray-finned fishes  Fins supported by membrane with spines called rays  These are the fish we eat