fish notes bi


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Kingdom – Animalia
Phylum – Chordata
Subphylum – Vertebrata


Include fish, amphibians, reptiles, birds, & mammals

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

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

Respire through pharyngeal or gill pouches during early development

Have post-anal tail in early stages

Endoskeleton made of bone &/or cartilage

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

Closed circulatory system

Taxonomy of Vertebrates:

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

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

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

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

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

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

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


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

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

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

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

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

Characteristics of  Fish:  

Streamlined body & muscular tail for swimming

Most with paired fins for maneuvering

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

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

Respire through gills

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.

Most with well-developed sense of sight & smell

Some can detect electrical currents

Ectotherms (adjust body temperature to environment)

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

Agnatha (Jawless Fish):

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

Circular mouths

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

Known as cyclostomes

Eel-shaped body

Mucus covers body

Skeleton made of cartilage

No paired fins

Gills without bony cover (called operculum)

Retain their notochord throughout their life

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

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


Includes sharks, rays, & skates

Endoskeleton of cartilage

Hinged jaws & paired fins

Placoid scales & tooth-like dermal spines on scales



Sharks are torpedo shaped

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

Shark Characteristics:

Fast swimmers

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

Tough, leathery skin

Fierce predators

Whale shark is largest & filter feeds on plankton

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

Short, straight intestine with spiral valve to slow food movement

5-7 pairs of gills for gas exchange

Kidneys remove wastes & maintain water balance

Electroreceptors on head help find prey & navigate

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

Separate sexes with external fertilization

Ray & Skate Characteristics:

Usually harmless to humans

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

Flattened bodies with ventral mouth

Both eyes on top of head

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

Feed on fish & invertebrates

Stingray with poison spine by tip of tail

Electric ray gives off strong, electric shock

Manta ray is largest

Traits of Bony Fish (Osteichthyes)

Skeleton made of bone

Hinged jaws

Paired fins

Gills for gas exchange

Lateral line

Body covered with scales & mucus coating

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

Lobe-finned Fish:

Muscular, paddle-like fins supported by bone


Known as coelacanths

Thought to be extinct until 1938 when species found in Africa

Live in deep oceans


Use lungs & gills

Eel-shaped body

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

Come to surface & gulp air when oxygen level is low

Form mud cocoon & become dormant if stream dries up

Ray-finned Fish:

Fan-like fins supported by rays

Includes salmon, perch, catfish, tuna, etc.

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

Four sets of gills covered by bony operculum

Have movable fins

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

Caudal fin or tail moves side to side to help steer

Pectoral fins (paired) on each side behind the operculum

Pelvic fins (paired) on ventral surface near the head

Anal fin (single) behind anus

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

Kidneys filter the blood & help maintain water balance

Ectothermic – body temperature regulated by the environment

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

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

Have separate sexes with external fertilization

Eggs hatch into fry

Salmon Life Cycle:

Migrate up to 3200 kilometers following magnetic cues in the ocean

Follow mucus trails when navigating rivers

Return to birthplace to spawn

Males change color & jaw lengthens & develops a hook

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

Male deposits sperm over eggs

Adults usually die after spawning

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

Secrete mucus coating in river as return to sea

May stay in ocean 6 months to 5 years