4. Diversity of Fishes

Kingdom - AnimaliaPhylum - Chordata

3 Classes: Agnatha, Chondrichthyes, Osteichthyes

Vertebrates:

• Ex: fish, amphibians, reptiles, birds, & mammals • Have a notochord (slim, flexible rod) present in early

stages - may be replaced by backbone in adults • Have a 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: 1. Class Agnatha: hagfish & lamprey-long,

eel-like bodies without jaws or paired fins & cartilage skeletons

Agnatha (Jawless Fish): • Hagfish& lampreys• Circular mouths that can’t close• Sharp teeth & strong, raspy tongue-tears hole in

prey & sucks out blood & body fluids• Eel-shaped body • Skeleton made of cartilage • No paired fins • Gills – no operculum• Hagfish: burrow in mud; scavenge on dead & dying

fish; have tentacles around their mouth • Lampreys: usually parasitic; great sense of smell to

find prey; covered with a poisonous slime

Lamprey with Prey

2. Class Chondrichthyes include sharks, rays, & skates also with cartilage

skeletons, paired fins, & jaws

Characteristics of  the more advanced fishes:  

• Streamlined body & muscular tail for swimming (know the differences between tail shapes!)

• Most - paired fins for maneuvering • Body covered with protective scales & mucus layer to

reduce friction when swimming • Respire through gills • Most - lateral line system-sensory structures running

down each side of the organism to detect changes in water temperature, pressure, current, etc.

• Most w/ well-developed sense of sight & smell • Most can detect electrical currents

• Ectotherms (body temperature close to outside temp.)

• Two chambered heart (1 atrium/1ventrical)

Class Chondrichthyes

• Includes sharks, rays, & skates

• Endoskeleton of cartilage

• Hinged jaws & paired fins

• Placoid scales & tooth-like dermal spines on scales

• Most Marine

• Most Carnivorous

Sharks vs. Rays

• Sharks are torpedo shaped=“fusiform”

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

Shark Characteristics:• Large, oily liver helps w/ buoyancy• Have countershading: protective coloration (darker top

& lighter bottom)• 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• Separate sexes - 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 countershading• 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 (Class 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

Ray-finned Fish:• Fan-like fins supported by rays • Includes salmon, perch, catfish, tuna, etc. • Have movable fins • Dorsal fin (s) located on top-keep fish upright &

used for defense • Caudal fin (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

Ray-finned Fish (cont.):

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

• Kidneys filter blood & help maintain water balance • Ectothermic - body temperature regulated by envt.• 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 & external fertilization • Eggs hatch into fry

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

Four sets of gills covered by bony operculum

External Anatomy of a Bony Fish

Guess What These Are:

Sites for Help on Vertebrates & Fish in Particular

• http://www.infovisual.info/02/033_en.html

• http://kentsimmons.uwinnipeg.ca/16cm05/1116/chordate.htm

• http://www.fishbase.org/home.htm