SKATES AND RAYS Have greatly enlarged pectoral fins

SKATES AND RAYS: • Have greatly enlarged pectoral fins and much reduced dorsal and caudal fins - pectoral fins forward motion • Rays move by bringing their fins up and down in the water - like wings • Skates travel by creating a wave that sweeps along the fin - they glide along the bottom • They have gills on their undersides and spiracles on the dorsal side - water enters through the spiracles and exits through the gills

RAYS: • Electric rays have organs in their heads that produce electric current • Stingrays have hollow barbs connecting to poison glands • Most rays are ovoviviparous, whereas skates are oviparous • Sawfish are related - have barbs on rostrum

CLASS OSTEICTHYES: THE BONY FISHES

BONY FISHES • The coelacanth and marine sturgeon are two of the most primitive bony fishes • The coelacanth (a lobe-finned fish) are found deep in the Pacific - until recently (1938) they were believed to be extinct • Marine sturgeons exhibit a heterocercal tail and have ganoid scales - which are thick and heavy scales, like armor

SCALES

A LIVING FOSSIL!

MODERN BONY FISH: • Modern bony fish have homocercal tails and their vertebral column does not extend down into the caudal fin • They have either cycloid or cteniod scales which are lighter and more flexible beneficial for faster swimming • Possess both paired and unpaired fins dorsal/ventral fins aid in stability and the paired fins are used to steer

BONY FISH

BODY SHAPE: • The streamlined body plan reduces drag from the water - allowing efficient movement • Shape is determined by the area in which the fish lives • Active swimmers have a fusiform body plan examples are tuna and marlin • Bottom dwelling fishes, like flounder, have flattened bodies

BODY SHAPE - contd. . . • Fish with sedentary lifestyles tend to have a globular body form (wider towards the belly) - example toadfish • Coral reef fishes are laterally compressed to navigate tight areas between coral • Burrowing fishes or those that live in tight areas, such as eels, have snakelike bodies and reduced appendages

COLOR: • Color also depends on where the fish lives • The color comes from chromatophores that are located just underneath the transparent scales • Fish that live in the deep sea exhibit obliterative countershading - dark on top and light colored underneath • Many coral reef fish use disruptive coloring - lines or spots are used to confuse predators

LOCOMOTION • Bony fish move by their trunk muscles - one side will contract and then the other, moving the tail from side to side and creating forward movement • Fish that swim slowly, like the eel, tend to undulate their entire body, whereas fast swimming fishes tend to primarily use their tails - this decreases the drag in the water

THE SWIM BLADDER: • A gas filled sac that helps to offset the fish’s density and keep them neutrally buoyant • Specialized networks of blood vessels add/remove the gases - this is necessary to stabilize buoyancy at varying levels • Fast swimming fishes do not have swim bladders because they swim so fast they would not have time to regulate gas levels - like sharks they must swim constantly to keep from sinking - ex. Yellowfin Tuna

RESPIRATION: • Gills remove oxygen from the water and filter out carbon dioxide • The gills are composed of rod-like structures called gill filaments • These filaments are highly vascularized the vessels run in the opposite direction of water flow - more efficient gas exchange • The operculum protects the gills and aids in respiration

SALINITY PROBLEMS: • The salinity is much lower in the tissues of marine fish than it is in their surrounding habitat - they tend to lose water through their gills • They compensate by drinking seawater however this brings too much salt into the fish - they deal with this three ways

Three ways to deal with too much salt. • Bony fish have salt secreting cells that line the gills and salt is secreted there • Some are eliminated in the feces • Other salts are secreted by the kidneys - a limited amount of urine is produced to help prevent additional water loss