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

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

FishHomeostasis

• 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

• 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

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