Introduction to Fish

What makes a fish a fish?

Jaws/ Mouths• Terminal:

Opens at midline

• Superior: Opens towards top of midline

• Inferior: opens downwards from midline

Scales• Cycloid: Fish

with smooth fins• Ctenoid: Fish

with bristled fins• Ganoid:

Primitive fish (gar or sturgeon)

• Placoid: Skin teeth or dermal denticles (sharks and triggerfish)

Gills• Respiration

(Oxygen & carbon dioxide exchange).

• Underneath gill openings, slits or operculum

Fins• Dorsal (2):

Stabilization• Pectoral (2):

Steering & stopping

• Pelvic (2): Stabilization

• Caudal (1): Propulsion & steering

• Anal (1): Stabilization

Swim Bladder• Buoyancy control• Some benthic

(bottom) fish do not have a swim bladder

• Sharks use their oily liver

Lateral Line• Sensory for

touch• Fluid filled

bulbs that sense water around the fish

There are 3 classes of fish

Agnatha• Fish without jaws• No scales• 7-14 gill openings• Very primitive• Hagfish or Slime

Eel: marine fish, scavengers

• Lamprey: Parasitic freshwater fish.

Chondrichthyes• Cartilage fish• Well-developed

jaws• 5-7 gill slits• Paired fins• Placoid scales• Sharks, skates,

rays and Chimaeras

Osteichthyes• Bony Fish• Paired fins• Gill cover

(Operculum)• Most have

scales• Tuna, damsels,

triggerfish, etc.