Fishes
Chapter 39
Introduction to Vertebrates
Section 39.1
Vertebrate Characteristics
• Only 1 phylum: Chordata
• Three distinguishing characteristics:
1. Vertebrae: bones or cartilage that
surrounds and protects dorsal nerve
cord (spine)
2. Cranium: skull that protects the brain
3. Endoskeleton composed of bone or
cartilage
Vertebrate Classification
• Nine Classes:
1. Hagfishes: elongated, eel-like bodies,
lack jaws, no paired fins, no
vertebrae (have notochord)
2. Lamprey: same as hagfish except
they have a primitive vertebrae
3. Sharks, Rays, & Skates: jaws, paired
fins, cartilage skeleton
4. Ray-finned Fish: jaws, bony skeleton,
Classification Continued
5. Lobed-finned Fish: fins on main axis of
body
6. Amphibians: thin & permeable skin,
eggs & larval stage in water
7. Reptiles: dry & scaly skin, eggs on
land
8. Birds: flight, feathers, hollow bones,
unique respiratory system
9. Mammals: hair, mammary glands
Vertebrate Evolution
• 560 million years ago
• First vertebrae = tadpole like, jawless
fish
Origin of Jaws
• 450 million years ago
• Evolved from first pair of
gill arches:
– skeletal elements that
protect pharynx
• Jaws aid in food seizure
and manipulation
Scientific Names:
• Hagfish
– Class Myxini
• Lamprey
– Class Cephalaspidomorphi
• Sharks, Rays & Skates
– Class Chondrichthyes
• Ray-Finned Fish
– Class Actinopterygii
• Lobed-Finned Fish
– Class Sarcopterygii
• Amphibians
– Class Amphibia
• Reptiles
– Class Reptilia
• Birds
– Class Aves
• Mammals
– Class Mammalia
Jawless & Cartilaginous Fishes
Section 39.2
Characteristics for the Water:
• Streamline body shape
• Strong muscular tail for propulsion
• Paired fins to maneuver in multiple
directions
• Secreted mucus to reduce friction
• Stored fat to help float
• Gills for respiration
Homeostasis
• Maintain homeostasis through osmosis
– osmoregulation
• Waste removal organs: kidneys & gills
– Kidneys filter wastes from blood &
removes excess water as urine
• Out through the cloaca
– Gills remove waste gases (CO2) and
excess ions directly into the water
Sensory functions
• Advanced senses to detect light, chemicals,
sound, electrical and magnetic fields
– Chemoreception: detect chemicals in the form
of smell and taste
• Lateral line system:
– Row of sensory structures that run the length of
the fish’s body on each side
– Connected by nerves to the brain
– Detects vibrations in water
Jawless Fishes
• Hagfish (Class Myxini):
– Bottom dwellers, marine habitat
– No vertebrae (have notochord)
– Mouth with two movable plates & rough
tongue-like structure
• Burrow into body eat from the inside out
• Lamprey (Class Cephalaspidomorphi) :
– Some are parasitic on other fish
– Disk-shaped mouth with rough tongue
that scrapes a hole into host
Cartilaginous Fishes
• Class Chondrichthyes
• Examples: Sharks, rays, & skates
• Skeletons made of cartilage:
– Flexible, lightweight material made of
cells surrounded by tough fibers of protein
• Carnivores
• Skin covered with placoid scales:
– Small, tooth-like spines that feel like
sandpaper
Adaptations
• Gills for respiration
– Fast swimming or pumping water over gills
– Rays & skates have spiracles to draw in
water
• Rectal gland: end of intestine that
removes excess ions from the blood
and releases into rectum for
elimination
• LARGE liver stores lipids to maintain
buoyancy
Reproduction
• Internal fertilization
• Male inject sperm into female with
modified pelvic fins called claspers
• Many cartilage fish have live birth
• No parental care once born
Rays & Skates
•
•
•
•
Flattened bodies
Wing-like pectoral fins
Bottom dwellers
Most feed on mollusks and crustaceans
Sharks
• Pectoral fins: just behind head, jut out
from body like wings of a plane
• 20,000 teeth during lifetime!
– Multiple rows
• Olfactory bulbs: part of brain that
detect smells from paired nostrils
• Fusiform: smooth, torpedo-shaped
bodies that reduce turbulence
Abdominal Cavity
Digestive Tract
Liver
Reproductive Organs
Dissection video
Bony Fishes
Section 39.3
Characteristics
• Bone: harder & heavier than cartilage
• Lungs or swim bladder: early fish have
lungs, most have a swim bladder (gas
filled sac used to control buoyancy)
• Scales: protect fish & reduce water
resistance
Lobed-Finned Fishes
• Fleshy fins
• Example: lungfish
– Breath through lungs and gills
– Live in shallow tropical ponds
– Ancestors of amphibians & other terrestrial
vertebrates
Ray-Finned Fish
• Rays: long, segmented, flexible bony
elements that support the fins
– Evolved from scales
• Diverse in appearance, behavior, &
habitat
• Familiar fish
External Anatomy
• Distinct head, trunk, & tail regions
• Operculum: hard plate that opens toward
the rear and covers & protects gills
• Caudal fin: extends from tail & moves side to
side
• Dorsal fins: anterior & posterior
• Pelvic fins & pectoral fins: help navigate fish
• Scales: skin of fish that grow quickly when
food is abundant
– Growth rings
Dorsal Fin
Caudal Fin
Operculum
Pectoral Fin
Pelvic Fin
Anal Fin
Internal Anatomy
• Skeleton = skull, spinal column,
pectoral girdle, pelvic girdle, & rib
• Pectoral girdle: where pectoral fins
attach
– shoulders
• Pelvic girdle: where pelvic fins attach
– hips
Digestive System
• Generalized carnivores
• Predatory fish have jaws lined with
inward pointing teeth
• Path of food:
– Mouth  pharynx (throat cavity) 
esophagus  stomach + enzymes 
intestines (absorption of nutrients) +
gallbladder that excretes bile (breaks
down fats) from liver + pancreas’
enzymes anus
Circulatory System
• Delivers oxygen & nutrients and
removes waste carbon dioxide &
ammonia
• Consists of heart, blood vessels like
capillaries, veins, & arteries
The Heart
• Two chambers in a row
• Sinus venosus: deoxygenated blood
empties into this collection area
1. Atrium: contractions move blood to
the ventricle
2. Ventricle: main pumping chamber
• Conus arteriosus: valves to prevent
backflow of blood
Respiratory System
• Water goes into mouth, past gill
filaments and out the operculum
• Blood flows in a countercurrent flow
opposite of water flow
– Allows for more O2 diffusion
Excretory System
• Kidneys: dissolve chemical wastes from
blood resulting in urine (with ammonia)
• Urinary bladder: holds urine until
expelled
Swim Bladder
• Thin walled sac in abdominal cavity
• Contains a mixture of O2, CO2, and N2
• Enables movement up and down
Nervous System
• Contains brain, spinal cord, nerves, &
sensory organs
• Most sensory organs connected to
brain via cranial nerves
The brain
• Olfactory bulb: processes info of smell
• Cerebrum: integrates information for
other areas of the brain
• Optic tectum: processes info of sight
• Cerebellum: coordinates motor output
• Medulla oblongata: controls body
functions
Reproduction
• Spawning: reproductive behavior of
fish
• Eggs & sperm released into water
through opening behind anus
• Most fish use external fertilization
Fish Dissection
Close-up: Body Cavity
Ovary
Muscle
Swim
Bladder
Eggs
Liver
Gastric
Cecae
Spleen
Small
Intestine
Stomach
Anterior View
1. Gills
2. Heart
3. Liver
4. Pyloric caeca
5. Small intestine
6. Stomach
7. Swim bladder
Posterior View
1. Swim bladder
2. Gonad
3. Large intestine
4. Urinary bladder
5. Anus