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 brain3. 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

• 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

• Class Chondrichthyes

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

Anal Fin

Pelvic Fin

Pectoral Fin

Operculum

External Anatomy

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

Muscle

Swim Bladder

Liver

Spleen

Gastric Cecae

Eggs

Stomach

Ovary

Small Intestine

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