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
Fish 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
Fish
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
Fish 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