Taxonomy of Fishes Chapter 18 The Fishes Kingdom Animalia Phylum Chordata SuperClass Agnatha - jawless fish Class Chondrichthyes - cartilagenous fish Class Osteichthyes - bony fish I. SuperClass Agnatha Characteristics Jawless No paired appendages Eel body shape Pore like gill openings 2 groups: Myxini and Cephalaspidomorphi A. Class Myxini Hagfish About 20 species Lack vertebrae Have sensory tentacles Exude large amounts of slime Eat by entering dead or dying fish and eating the insides leaving only the skin 1
B. Cephalaspidomorphi Lampreys Adults prey on fish while juveniles are filter feeders Androminous (leave the sea and swim to freshwater streams to spawn) Attach to fish using sucking mouth parts and scrape away scales with teeth to feed on blood of the fish II. Class Chondrichthyes Sharks, skates, rays, ratfish Carnivores and scavengers, most marine Biting mouth parts and paired appendages Placoid scales and cartilagenous endoskeleton Muscles are zigzag bands called myomeres Kidneys regulate salt levels in the body 2
A. Sharks Tough skin with placoid scales Teeth are usually modified placoid scales Most are not aggressive Species that can be dangerous to humans Great White, Mako, Tiger, Hammerhead Can detect prey 1km away or more Olfactory organs (smell) Chemicals as low as 1ppb Lateral line detects low frequency vibrations B. Rays and Skates Expansion of pectoral fins laterally into wing-like projections Shallow water, bottom dwellers Feed on invertebrates Spiracles on top of head take in water for respiration Gill openings are on the underside of the head 3
III. Class Osteichthyes Characteristics Bony skeleton Operculum covering gill openings Lungs (in some) Swim bladder 24,000 + species A. Subclass Sarcopterygii Lobe finned fish Only 7 species exist Lung Fish Ceolacanths Believed to be extinct but were re-discovered off the coast of Madagascar in 1938 Deep metallic blue w/irregular white or brassy flecks which provide camoflauge against the dark lava cave reefs they inhabit Diphycercal tail Young born fully formed after hatching from internal eggs Diphycercal tail Can live out of water (lungs and gills) Australian - out of water for short periods of time S. American & African -can live out of water for long periods of time 4
B. Subclass Actinopterygii Ray-finned fishes Have swim bladders - gas-filled sacs on the dorsal side to regulate buoyancy Chondrosteans Sturgeons and Paddlefish Teleosts Lead to modern bony fish C. Teleosts a.k.a. Neopterygians 23,600 described species (5-10,000 undescribed species) Homocercal tail - more speed Fleixble dorsal fin: camouflage, breaking and other complex movements, streamlining, & social communication Paired and medial fins supported by long dermal rays Muscle controlled fin movement IV. Structural and Functional Adaptations of Fish A. Locomotion - swimming Propulsion by trunk and tail muscles Average fish speed is 10.4 km (6.5 miles) per hour Most economical form of locomotion - little energy needed to overcome gravity, streamlined body shape, and mucous secretions 5
B. Nutrition & Digestion Most are predators Some filter feeders and use gill rakers to trap plankton while the fish has mouth open Stomach stores food Small intestine is primary site for digestion Bony fish have pyloric ceca (outpockets of intestine for increased absorption) C. Circulation & Gas Exchange Closed circulatory system with a two chambered heart Atrium & ventricle Ram Ventilation - used by sharks Maintain water flow over gills by keeping mouth open while swimming Gills Gill arches - support structure to hold up gill filaments Gill filaments - extension of gill arches that contains vessels carrying blood to & from gas exchange surfaces D. Buoyancy Regulation Incorporate fats into their tissues (livers) Use fins to provide lift Pectoral fins act as planing devices Caudal fin provides upward thrust Reduction of heavy tissues Bones are less dense Swim bladder Fill with air E. Nervous & Sensory Functions Brain & spinal cord External nares - openings to olfactory bulb Inner Ear - equilibrium & balance Middle Ear - detecting sound Lateral-line system - detect water currents, predator-prey, low-frequency sounds 6
F. Electroreception & Electric Fishes Electroreception - detection of electrical fields that another organism generates Used by over 500 species of fishes to detect prey Electric fishes Muscles near caudal fin modified into organs that produce a continuous electrical current Can deliver a shock between 50-500 volts+ Stun/kill prey, discourage predators, keep away humans G. Excretion & Osmoregulation Paired kidneys on the dorsal side Rid the blood of wastes Help control the amount of water in tissues Saltwater fish - kidneys dilute the amount of salt Freshwater fish- pump out large amounts of dilute urine Nitrogenous wastes are eliminated in the form of ammonia H. Reproduction Fertlization can be external or internal depending on the species Oviparous - eggs hatch outside of the mother s body Ovoviviparous - eggs stay in the mother s body after internal fertilization, hatch and then are born alive Viviparous - obtain nutrition directly from the mother, not an egg, and are born alive (most sharks) 7