Fish

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Kingdom - Animalia
Phylum -
Chordata
Subphylum -
Vertebrata

Vertebrates:

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Include fish, amphibians, reptiles, birds, & mammals

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Have a notochord (slim, flexible rod) present in early stages that may be replaced by backbone in adults

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Contain a dorsal, hollow bundle of nerves called the nerve or spinal cord

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Respire through pharyngeal or gill pouches during early development

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Have post-anal tail in early stages

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Endoskeleton made of bone &/or cartilage

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Anterior head with well developed brain & sensory organs (Cephalization)

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Closed circulatory system

Taxonomy of Vertebrates:

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Agnatha include hagfish & lamprey with long, eel-like bodies without jaws or paired fins & cartilage skeletons

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Chondrichthyes include sharks, rays, & skates with cartilage skeletons, paired fins, & jaws

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Osteichthyes are bony fish with jaws, paired fins, & bone and cartilage in their skeletons

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Amphibia include frogs, toads, & salamanders that go through an aquatic larval or tadpole stage

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Reptilia include snakes, turtles, lizards, & alligators that live on land, are covered with scales, & lay a tough, protective amniote egg

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Aves are birds covered with feathers, adapted for flying, & with hollow bones

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Mammalia have hair or fur & females have mammary or milk-producing glands

Evolution:

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Fossil record shows jawless fish without paired fins appeared first about 550 million years ago

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Ostracoderm was a jawless, bottom-feeding ancestor to the agnathans (modern jawless fish)

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Development of jaws & paired fins allowed better movement & increased ability to capture prey

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Extinct acanthodians or spiny fish were first jawed fish with paired fins

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Jaws probably developed from gill arches (bone that supports the pharynx)

Characteristics of  Fish:   goldfish.gif - 9172 Bytes

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Streamlined body & muscular tail for swimming

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Most with paired fins for maneuvering

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Body covered with protective scales & mucus layer to reduce friction when swimming

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Have less dense body tissues & store less dense lipids to help them float

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Respire through gills

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Most have a lateral line system or a row of sensory structures running down each side of the organism to detect changes in water temperature, pressure, current, etc.

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Most with well-developed sense of sight & smell

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Some can detect electrical currents

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Ectotherms (adjust body temperature to environment)

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Two chambered heart (upper atrium receives blood & lower ventricle pumps blood)

Agnatha (Jawless Fish):

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Hagfish (live in oceans) & lampreys (found in marine & freshwater)

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Circular mouths

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Sharp teeth & strong rasp-like tongue to tear hole in prey & suck out blood & body fluids

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Known as cyclostomes

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Eel-shaped body

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Mucus covers body

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Skeleton made of cartilage

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No paired fins

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Gills without bony cover (called operculum)

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Retain their notochord throughout their life

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Hagfish are bottom dwellers in cold marine waters that burrow in mud, scavenge on dead & dying fish, & have tentacles around their mouth

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Lampreys are usually parasites with a keen sense of smell to locate prey, lay their eggs in freshwater streams, & are covered with a poisonous slime

Chondrichthyes
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Includes sharks, rays, & skates

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Endoskeleton of cartilage

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Hinged jaws & paired fins

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Placoid scales & tooth-like dermal spines on scales

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Marine

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Carnivorous

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Sharks are torpedo shaped

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Rays & skates have broad, flat bodies with wing-like fins and a tail

Shark Characteristics:
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Fast swimmers

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Large, oily liver (20% of body weight) makes them buoyant

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Tough, leathery skin

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Fierce predators

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Whale shark is largest & filter feeds on plankton

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Ventral mouth with 6-20 rows of sharp, replaceable teeth

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Short, straight intestine with spiral valve to slow food movement

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5-7 pairs of gills for gas exchange

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Kidneys remove wastes & maintain water balance

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Electroreceptors on head help find prey & navigate

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Lateral line along side of body contains sensory cells to detect vibrations & pressure

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Separate sexes with external fertilization

Ray & Skate Characteristics:

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Usually harmless to humans

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Broad, wing-like pectoral fins used to glide through water

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Flattened bodies with ventral mouth

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Both eyes on top of head

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Have protective coloration (darker on top & lighter on bottom)

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Feed on fish & invertebrates

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Stingray with poison spine by tip of tail

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Electric ray gives off strong, electric shock

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Manta ray is largest

Traits of Bony Fish (Osteichthyes)

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Skeleton made of bone

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Hinged jaws

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Paired fins

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Gills for gas exchange

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Lateral line

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Body covered with scales & mucus coating

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Includes lobe-finned, ray-finned, and lung fish

Lobe-finned Fish:

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Muscular, paddle-like fins supported by bone

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Gills

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Known as coelacanths

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Thought to be extinct until 1938 when species found in Africa

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Live in deep oceans

Lungfish:

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Use lungs & gills

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Eel-shaped body

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Live in shallow, tropical rivers of Africa, Australia, & South America

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Come to surface & gulp air when oxygen level is low

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Form mud cocoon & become dormant if stream dries up

Ray-finned Fish:

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Fan-like fins supported by rays

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Includes salmon, perch, catfish, tuna, etc.

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Body covered with round, overlapping cycloid or ctenoid scales & mucus

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Four sets of gills covered by bony operculum

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Have movable fins

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Dorsal fin(s) located on top keep fish upright & used for defense

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Caudal fin or tail moves side to side to help steer

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Pectoral fins (paired) on each side behind the operculum

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Pelvic fins (paired) on ventral surface near the head

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Anal fin (single) behind anus

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Swim bladder is thin-walled sac in abdomen that creates buoyancy from diffusion of dissolved gas from blood


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Kidneys filter the blood & help maintain water balance

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Ectothermic - body temperature regulated by the environment

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Keen sense of smell (nostrils) & have chemical receptors over the body

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Can detect the earth's magnetic field as a guide to navigate oceans

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Have separate sexes with external fertilization

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Eggs hatch into fry

Salmon Life Cycle:
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Migrate up to 3200 kilometers following magnetic cues in the ocean

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Follow mucus trails when navigating rivers

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Return to birthplace to spawn

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Males change color & jaw lengthens & develops a hook

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Female uses her tail to build gravel nest & lays up to 10,000 eggs 

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Male deposits sperm over eggs

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Adults usually die after spawning

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Pacific salmon return to sea when 15 cm long; while Atlantic salmon may stay in river up to 7 years

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Secrete mucus coating in river as return to sea

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May stay in ocean 6 months to 5 years