Fishes

and

Amphibians

Chapter 28

Section 28.1

What is a fish?

• Fishes, like all vertebrates, are classified in the phylum Chordata.

• Fishes belong to the subphylum Vertebrata.

What is a fish?

• In addition to fishes, subphylum Vertebrata includes amphibians, reptiles, birds, and mammals.

What is a fish?

• In vertebrates, the embryo’s notochord is replaced by a backbone in adult animals.

• All vertebrates are bilaterally symmetrical, coelomates that have endoskeletons,( made of

cartilage

or bone) closed circulatory systems, nervous systems with complex brains and sense organs, and efficient respiratory systems.

• * is a tough, flexible material

Section 1 Fishes and Amphibians Fishes

Neural Crest  A neural crest is a group of cells that develop from the nerve cord in vertebrates.

 Portions of the brain and skull, certain sense organs, and some nerve fibers are some of the structures that develop from the neural crest.

Key Characteristics of Modern Fishes

• Despite the variation – all fish have Gills, single loop blood circulation, and a backbone.

1.Fish breathe using gills

• Fish have gills made up of feathery

gill filaments

that contain tiny blood vessels through which gases enter and leave the blood.

Gill Filaments

Fishes breathe using gills

• As a fish takes water in through its mouth, water passes over the gills and then out through

gill slits

side of the fish. at the • Gill cover= operculum

Gill Filaments

• Oxygen and carbon dioxide are exchanged through the capillaries in the gill filaments. In a

countercurrent flow

.(=blood flows in one direction and water in the opposite direction.)

Water Artery Vein Capillary networks in filament Gill filaments

Water

2.

Single-loop blood circulation-

• Blood is pumped from the heart to the capillaries in the gills.

• From the gills , blood passes to the rest of the body and then returns to the

Heart

. • a.)

Sinus Venous-

collection chamber- reduces the resistance of blood flow into the heart.

• b.)

Atrium

- delivers blood to ventricle • c.)

Ventricle

- forces blood to flow through the gills and eventually to the rest of the body.

• d.)

Conus arteriosus-

smoothes the pulsations and adds still more force. • Lungfishes are an exception they have a double loop.

Fishes have two-chambered hearts

Aorta Gills Capillary network Heart

5. Reproduction

• Although the method may vary, all fishes reproduce sexually .

• Fertilization and development is external in most fishes.

• Eggs and sperm can be released directly into the water, or deposited in more protected areas, such as on floating aquatic plants.

• A yolk sac within each egg contains nutrients the developing embryo will need for growth.

Fishes reproduce sexually

• Most bony fishes have external fertilization and development.

• This type of external reproduction in fishes and some other animals is called spawning .

Salmon spawning

Fishes reproduce sexually

• Cartilaginous fishes have internal fertilization.

• Skates deposit fertilized eggs on the ocean floor.

• Some female sharks and rays carry developing young inside their bodies.

• A few species of sharks lay eggs.

• During mating, the male uses two organs called

claspers

to insert sperm into the female.

Fishes reproduce sexually

• In some bony fishes, such as guppies and mollies, fertilization and development is internal.

• Most fishes that produce millions of eggs provide no care for their offspring after spawning.

• Some fishes, such as the mouth-brooding cichlids, stay with their young after they hatch.

Most fishes have paired fins

• Fishes in the classes Chondrichthyes and Osteichthyes have paired fins.

• Fins are fan-shaped membranes that are used for balance, swimming, and steering.

3. Vertebral column (backbone)

• made of either cartilage or bone • Surrounds the spinal cord • Brain is encased with the skull or cranium.

4.

Kidneys Nephrons

- are tube-like units that regulate the body’s salt and water balance and remove metabolic wastes from the blood.

Freshwater fish excrete large amounts of urine compared to marine fish due to osmosis and ion exchange.

* to make up for the water they lose by osmosis, marine fish drink sea water & pump out excess ions out of their bodies.

Most fishes have paired fins

• Fins are attached to and supported by the endoskeleton and are important in locomotion.

Most fishes have paired fins

• The paired fins of fishes foreshadowed the development of limbs for movement on land and ultimately of wings for flying.

Pectoral fin Dorsal fins Caudal fin Anal fin Pelvic fins

Fishes have developed sensory systems

• The lateral line system is a line of fluid-filled canals running along the sides of a fish that enable it to detect movement and vibrations in the water.

Lateral line Gelatin-like fluid Receptor cells Nerve

Fishes have developed sensory systems

• Fishes have eyes that allow them to see objects and contrasts between light and dark in the water as well.

• Some fishes that live in areas of the ocean where there is no light may have reduced, almost nonfunctional eyes.

Fishes have developed sensory systems

• Some fishes also have an extremely sensitive sense of smell and can detect small amounts of chemicals in the water.

• Sharks can follow a trail of blood through the water for several hundred meters.

Section 1 Fishes and Amphibians

Scales  There are four types of fish scales .

 Ctenoid scales- tooth  Placoid scales made of tooth like material and like a comb are rough and heavy  Cycloid scales made of bone and skin (shark)  Ganoid scales made of enamel and bone

Jaws evolved in fishes

Gill arches

Gill slits

Jawless, filter-feeding fish Skull

Gill slits Gill arches

Beginning of jaw formation

Fish with jaws

• The gill arches evolved to form the jaw!!

Jaws

Jaws evolved in fishes

Gill arches

Gill arches Gill slits Gill slits Skull Jawless, filter-feeding fish Beginning of jaw formation Fish with jaws

• Jaws also allowed early fishes to prey on a greater variety of organisms. • The advantage of jaws is that they enable an animal to grasp and crush its prey with great force

Jaws

Jaws evolved in fishes

• Sharks have up to 20 rows of teeth that are continually replaced.

• Their teeth point backwards to prevent prey from escaping once caught.

Jaws evolved in fishes

• Sharks are among the most streamlined of all fishes and are well adapted for life as predators.

Most fishes have bony skeletons

• Bony fishes, a successful and widely distributed class, differ greatly in habitat, size, feeding behavior, and shape.

Classes of fishes

Fishes Class

Myxini Cephalaspidomorphi Chondrichthyes Osteichthyes

Organisms

Hagfishes Lampreys Sharks, skates, rays Lobe-finned fishes, ray-finned fishes

Characteristics

Jawless, cartilaginous skeleton, gills Jawless, cartilaginous skeleton, gills Jaws, cartilaginous skeleton, paired fins, gills, scales, internal fertilization Jaws, bony skeleton, paired fins, gills, scales, swim bladder

Bony fishes have separate vertebrae that provide flexibility

• The evolution of a backbone composed of separate, hard segments called vertebrae was significant in providing the major support structure of the vertebrate skeleton.

• Separate vertebrae provide great flexibility.

Bony fishes evolved swim bladders

• A fish with a swim bladder can control its depth by regulating the amount of gas in the bladder.

Swim bladder

Bony fishes evolved swim bladders

• Some fishes remove gases from the swim bladder by expelling them through a special duct that attaches the swim bladder to the esophagus.

• In fishes that do not have this duct their swim bladders empty when gases diffuse back into the blood.

A Bony Fish

Lateral line system Swim bladder Kidney Urinary bladder Reproductive organ Fins Stomach Intestine Liver Heart Scales Gills

Section 28.2

Diversity of fishes

• Fishes range in size from the tiny dwarf goby that is less than 1 cm long, to the huge whale shark that can reach a length of about 15 m

—

the length of two school buses.

Whale shark

Agnathans are jawless fishes

• Lampreys and hagfishes belong to the superclass Agnatha.

Lamprey

• The skeletons of agnathans, as well as of sharks and their relatives, are made of a tough, flexible material called cartilage .

• Lampreys and Hagfish have a

notochord

all stages of their life. (even adulthood) in

Agnathans are jawless fishes

• A hagfish has a toothed mouth and feeds on dead or dying fishes.

• It can drill a hole into a fish and suck out the blood and insides.

• Parasitic lampreys use their suckerlike mouths to attack other fishes.

• They use their sharp teeth to scrape away the flesh and then suck out the prey’s blood.

Sharks and rays are cartilaginous fishes

• Sharks, skates, and rays belong to the class Chondrichthyes .

• These fishes, like agnathans, possess skeletons composed entirely of cartilage.

• Sharks are perhaps the most well-known predators of the oceans.

Sharks and rays are cartilaginous fishes

• Like sharks, most rays are predators and feed on or near the ocean floor.

• Ras have flat bodies and broad pectoral fins on their sides.

Sharks and rays are cartilaginous fishes

• By slowly flapping their toes up and down, rays can glide as they search for mollusks and crustaceans along the ocean floor.

Subclasses of bony fishes (see p. 831)

• Scientists recognize two subclasses of bony fishes —the lobe-finned fishes, including lungfishes, and the ray-finned fishes.

• The lobe-finned fishes are represented by seven living species: six species of lungfishes, which have both gills and lungs, and the coelacanth.

• Each fin consists of a long, fleshy muscular lobe that is supported by a central core of bones.

• A third group (now extinct) - Is the tetrapod

Subclasses of bony fishes

• In the ray-finned fishes , such as catfish, perch, salmon, and cod, fins are fan-shaped membranes supported by stiff spines called

rays.

•

Teleosts-

mobile fins have highly • Very thin scales • Completely symmetrical tails • 95% of all ray finned fish are teleosts.

Perch

Evolution of Fishes

• Scientists have identified fossils of fishes that existed during the late Cambrian Period, 500 million years ago.

• At this time, ostracoderms (OHS trah koh durmz), early jawless fishes, were the dominant vertebrates on Earth.

Origins of Fishes

Anaspid Heterostracah Cephalaspid

Origins of Fishes

• Bone provides a place for muscle attachment, which improves locomotion.

• In ancestral fishes, bone that formed into plates provided protection as well.

Origins of Fishes

• Scientists hypothesize that the jawless ostracoderms were the common ancestors of all fishes.

• Modern cartilaginous and bony fishes evolved during the mid-Devonian Period.

• Lobe-finned fishes, such as coelacanths (SEE luh kanths), are another ancient group, appearing in the fossil record about 395 million years ago.

Key Characteristics of Amphibians

• Legs- most have 4, Caecilians have none.

• Amphibians have thin, moist skin ( cutaneous respiration) • Lungs- is an internal , baglike respiratory organ.

-In the larval form they have gills not lungs.

4. Double Loop circulation

• Two large veins called pulmonary veins return oxygen rich blood from the lungs to the heart.

• The evolution of the three-chambered heart in amphibians ensured that cells received the proper amount of oxygen.

• Blood from both chambers then moves to the third chamber, (= ventricle ) which pump oxygen-rich blood to body tissues and oxygen-poor blood back to the lungs and skin so it can pick up more oxygen.

5. Partially Divided Heart

• In the three-chambered heart of amphibians, one chamber receives oxygen-rich blood from the lungs and skin, and another chamber receives oxygen-poor blood from the body tissues. (= atrium ) divided into left and right sides.

•A dividing wall known as the septum separates the atrium into a right and left.

6. Cutaneous Respiration-

amphibians have thin, moist skin which they use to supplement their oxygen content.

Frogs and toads belong to the order Anura

• Frogs and toads are amphibians with no tails.

• Frogs have long hind legs and smooth, moist skin.

Frog Toad

Frogs and toads belong to the order Anura

• Toads have short legs and bumpy, dry skin.

• Adult frogs and toads are predators that eat invertebrates, such as insects and worms.(=carnivorous)

Frog Toad

• Because the skin of an amphibian must stay moist to exchange gases, most amphibians are limited to life on the water’s edge or other moist areas.

Frogs and toads belong to the order Anura

• Most frogs and toads spend part of their life cycle in water and part on land.

• They breathe through lungs or through their thin skins.

• Declining numbers of frog species, or deformities in local frogs, sometimes indicate the presence of pollutants in the environment.

Eyes A Frog Tongue

Vocal cords

Lungs

Heart

Calls Tympanic membrane

Backbone Fat bodies Intestine Liver

Legs

Frogs and toads belong to the order Anura

• Frogs and toads also have vocal cords that are capable of producing a wide range of sounds. Vocal cords are sound-producing bands of tissue in the throat.

Reproduction in Frogs

• Fertilization in most amphibians is external, and water is needed as a medium for transporting sperm.

• Amphibian eggs lack protective membranes and shells and must be laid in water or other moist areas.

Amphibians undergo metamorphosis

Fertilized eggs Young, legless tadpoles live off yolk stored in their bodies.

Adult frog Young frogs have structures needed for life on land.

Tadpoles with legs feed on plants in the water.

Metamorphosis of a Frog

•

Tadpole

• -Herbivore • -Gills • - tail • -no legs • 2 Chambered heart •

Adult

• -Carnivore • -Lungs • -no tail • -legs • 3 chambered heart

Amphibians undergo metamorphosis

• Young salamanders resemble adults, but, as aquatic larvae, they have gills and usually have a tail fin.

• Most adult salamanders lack gills and fins.

• They breathe through their moist skin or with lungs.

Amphibians undergo metamorphosis

• Completely terrestrial salamander species do not have a larval stage; the young hatch as smaller versions of adults.

• Most salamanders have four legs for moving about, but a few have only two front legs.

Amphibians are ectotherms

• An ectotherm (EK tuh thurm) is an animal that has a variable body temperature and gets its heat from external sources.

• Because many biological processes require particular temperature ranges in order to function, amphibians become dormant in regions that are too hot or cold for part of the year.

Mudpuppy

Salamanders belong to the order Caudata

• A salamander has a long, slender body with a neck and tail.

• Salamanders resemble lizards, but have smooth, moist skin and lack claws.

Salamanders belong to the order Caudata

• They range in size from a few centimeters in length up to 1.5 m. The young hatch from eggs, look like small salamander adults, and are carnivorous.

Caecilians belong to the order Gymnophiona

• Caecilians are burrowing amphibians, have no limbs, and have a short, or no tail (=wormlike) • Caecilians are primarily tropical animals with small eyes that often are blind.

• They eat earthworms and other invertebrates found in the soil.

• All caecilians have internal fertilization.

Challenges of life on land

• Amphibians first appeared about 360 million years ago.

• Amphibians probably evolved from an aquatic tetrapod around the middle of the Paleozoic Era.

Challenges of life on land

• Able to breathe through their eyes, butt, or fingers, amphibians became, for a time, the dominant vertebrates on land.

Challenges of life on land