Fish Characteristics
· Locomotion: trunk and tail used for propulsion
o Undulation of entire body in slow swimmers
o Fast swimmers only undulate tail region.
· Buoyancy: all fish are slightly heavier than water and have tendency to sink.
o Sharks move forward at all times to prevent sinking.
o Bony fish have swim-bladders: adjusting volume of gas inside can allow suspension without muscular effort.
§ Regulating gas in the swim bladder
· Pneumatic duct: connects swim bladder to esophagus
· Gas gland: enables gas exchange with blood
o Rete mirabile: “marvelous net” of capillaries that function as a countercurrent exchange system to trap gases
· Respiration
o Gills are composed of thin filaments richly supplied with blood vessels.
o Operculum: moveable flap that protects gills and streamlines body
· Reproduction and Growth
o Most dioescious with external fertilization
o Eggs usually hatch into larvae that undergo metamorphosis into adults
§ Most oviparous: egg producing
§ Some ovoviviparous: egg-producing, live birth (no placenta)
§ Some sharks viviparous: live birth with internal nourishment
· Agnatha: Jawless Fish
o Adapted as scavengers or parasites
o Eel-like body form
o No vertebrae, but cranium present
o No jaws, internal bones, scales, paired fins
o Pore-like gill openings
o Hagfish
§ Keen sense of smell for finding dying prey
§ Attach to prey with toothed plates and then rasps away tissue with tongue
§ Both male and female gonads present, but only one becomes functional
§ No larval stage
o Lampreys
§ Both marine and freshwater forms
§ Petromyzon marinus is found in Great Lakes
o Can hold stones in mouth to hold position in current
o Males build nests for females to lay eggs in
o Eggs hatch and release larvae that stay in the nest and later buried for 3-17 years
· Chondrichthyes: Cartilaginous Fish
o Skeleton composed of cartilage
o Well-developed sense organs
o Powerful jaws and swimming musculature
o Primarily predators
§ Sharks
· Predaceous fish with five to seven gill slits and gills on each side
· Typically a spiracle behind each eye
· Leathery skin covered with placoid scales made of dentine
· Lateral line system is used to locate objects
· Can also detect bioelectric fields generated by animals
§ Rays
· Similar to sharks in many ways
· Propel bodies with wave-like motions of pectoral fins
· Dorsoventrally flattened bodies with gill openings on underside of head
· Large spiracles
· Slender, whiplike tails that can be armed with one or two spines
· Skates: group of rays characterized by muscular tail and arrangement of fins
o Produce “mermaid’s purse”=large, yolky egg enclosed within a horny covering
· Chimaeras
o Includes ratfish, rabbitfishs, spookfish, and ghostfish
o Mixture of shark-like and bony-like traits
· Osteichthyes: Bony fish
o Large, diverse taxon
o Pectoral and pelvic fins present that are supported by bony girdles embedded in body musculature
o Have operculum covering gill slits
o Progressive specialization of jaw structure and feeding mechanisms
o High levels of activity
· Fleshy-finned Fish
o Only seven living species remain
§ 6 are lungfish, 1 is a lobe-finned fish
o Have lungs as well as gills with strong, fleshy paired lobed fins that can be used like legs to move about bottom
o Lungfish
§ Some are primitive and can survive in stagnant water, but not outside of water.
§ Others have adaptations for living outside of water.
§ African lungfish (Propterus)
· Can live in rivers that go completely dry
· Burrow down and secrete slime that mixes with mud to form a hard cocoon, allowing them to remain dormant until rains return.
o Lobe-finned Fish
§ Only living representative is the coelacanth
· Ray-finned Fish
o Includes all familiar bony fish
§ Many with cycloid and ctenoid scales, swim bladders