Fish and Amphibians

Chapter 30 TURBOBLAST Edition!

What is a fish??• All fish are:– Chordates, vertebrates, bilaterally symmetrical

coelomates– Have endoskeleton, closed circulatory systems,

nervous systems with complex brains & sense organs, efficient respiratory systems

• Ichthyology: the study of fish (Gr: icthyes = fish)

Four classes of FishAgnatha “without jaws” (Gr: gnatho = jaw)• 2 classses:

Chondrichthyes “cartilage fish”

Osteicthyes “bony fish”

Myxini

hagfish

Cephalaspidomorphi

lampreys

Chimaera sharks skates & rays

Fishes breath using gills

Fish takes in water through its mouth, water passes over gills and out side slits

Oxygen & carbon dioxide are exchanged through capillaries in gill filaments

Fish have hearts, too! • All fishes have two-chambered heart– One chamber receives deoxygenated blood, the

second chamber pumps blood directly to gills• Blood takes up oxygen in gills, pumped around the

body, then back to the heart

*This circulation allows fish to

efficiently make ATP through cellular

respiration!

Sexual reproduction• External fertilization in most fishes

– Simultaneous release of gametes into water– Sometimes deposited in protected areas

(plants, rocks, etc.)– Most fishes produce large #s of eggs at once,

some produce small # of larger eggs• Cartilaginous fish have internal fertilization

– Skates deposit fertilized eggs on ocean floor– Some sharks & rays carry developing young

inside bodies• Spawning – bony fish (external fertilization &

development), produce millions of eggs, provide little to no care for young, only a few survive until adulthood (ex. Salmon, cod) https://www.youtube.com/watch?v=Jgp6OjpfrQo

– Some adults protect young fry when threatened by danger (Ex. Gouramis, cichlids, tilapia http://youtu.be/QkmmpSrbbjM

Pairs of fins & Movement• Fish in Chondrichthyes and Osteichthyes have paired fins– Fins are fan-shaped membranes used for balance, swimming,

steering• Lobe-finned vs. Ray-finned fishes

– Lobe-finned fish have sturdy bone structure and stronger pectoral muscles, foreshadow the evolutionary development of all tetrapods on land

• Ray-finned fish have webbed spines, comprise 99% of all fish species

Sensory systems in fish• Lateral line system– Enables fish to sense objects and changes in their

environment• System of fluid-filled canals running along sides of fish,

detect vibrations & movement in the water

• Complex eyes– Can see objects and contrast in water• Vision varies greatly among fishes (some in darker waters

have reduced, almost nonfunctional eyes

• Sense of smell– Can detect extremely small amounts of chemicals in water, helps locate prey

Most Fish Have Scales

• Cartilaginous & bony fishes have skin covered by overlapping scales (like roofing tiles)– Can be classified by the types of scales– Scales are thin bony plates formed from the skin

Evolution of the Jaw• Jaws evolved in fishes– Have the advantage of grasping & crushing prey– Fish with jaws could feed on greater variety of food

• Sharks have up to 20 rows of razor-sharp teeth, pointing back into their mouth (stops prey from escaping)

Bony, flexible skeletons

• Osteichthyes are most successful fish group– Skeletons are mineralized

(w/ calcium) & rigid– Development of bone

allowed fish to adapt to variety of aquatic environments, and eventually to land

• Bony fishes have separate vertebrae for flexibility

Swim Bladders• Swim bladder is a thin-walled internal sac that

fish can contract to change gas/liquid concentration• Squeeze higher

pressure, gas dissolves into liquid, fish can descend deeper

• Relax lower pressure, gas accumulates into bubbles, fish can rise toward water surface

Fish Diversity• Hagfish & Lampreys are jawless, and feed with a

rasping, suckerlike mouth http://youtu.be/tKTRv3hx1s0 http://youtu.be/-SYhOD1Yx10

– Skeletons are made of flexible cartilage– Hagfish create thick slime to avoid predators, tie into knots

to slip out of tight spots while feeding http://youtu.be/pmaal7Hf0WA http://youtu.be/5kS64P-o5mU

• Sharks, skates and rays are cartilaginous fishes– Similar to 100,000 year old fossils, considered “living fossils”– Sharks are most well-known predators of the oceans

http://youtu.be/iLHTtDbtDFA

– Rays & skates have flat bodies, feed near ocean floor http://youtu.be/9D06j__CZHs

• Lobe-finned fishes – 6 species (ex. lungfish, coelacanth)• Ray-finned fishes - ~30,000 species (ex. catfish, perch,

salmon, cod) http://youtu.be/cIgHEhziUxU

Origins of Fish• Fossils from the Cambrian Period 500 mya show the existence

of fishes– Ostracoderms (early jawless fish) were dominant vertebrates

• Possessed a cartilage skeleton and bony head plate• Most were extinct by the end of Devonian Period 354 mya• Present-day agnathans appear to be direct descendants

• Ostracoderms swam sluggishly (weighed down by heavy, bony external armor)

• Development of calcified bone in early vertebrates was important for muscle attachment, improved locomotion

• Jawless ostracoderms are considered common ancestors of all fishes (and subsequent tetrapods)

• Lobe-finned fishes appeared 395 mya (ex. Coelacanth http://youtu.be/NzzxOlFJtzg, lungfish http://i306.photobucket.com/albums/nn263/headbanger_jib/protopterus%20annectens/DSC_7437.jpg

Amphibians• What is an amphibian?– Gr: Amphi = “both,” bio = life “double life”– Transition from aquatic larvae to air-breathing, semi-

terrestrial adult is unique in amphibians• 3 orders in class Amphibia:– Caudata (salamanders & newts)– Apoda (caecilians)– Anura (frogs & toads)

• All have moist skin, most have 4 legs, capable of terrestrial existence, rely on water for reproduction

Rely on external temperature• Amphibians are ectotherms, whose body

temps depend on external sources– Usually found in warmer habitats– Become dormant when temperature ranges

become too cold or too hot• Often bury themselves & wait out the harsh season

Metamorphosis• Fertilized egg tadpoles (aquatic stage of most amphibians)Tadpoles have fins, gills, 2-chambered heart like fish

Can avoid competition with adults by occupying a completely separate niche

Eventually develop legs, lungs, and a 3-chambered heart (needed for life on land)

• Young salamanders resemble adults but have gills and tail fins as larvae, while adults breathe only through skin

• Most salamanders have 4 legs, but some have just 2 front legs

Walking takes energy!

• Early amphibians required lots of food and oxygen to get around on land (they were uncoordinated on land)

• 3-chambered heart enabled oxygen-rich blood to reach body tissues more efficiently– Some mixing of oxygen-rich & oxygen-poor

blood happens, so as blood is pumped near skin, more gas exchange occurs across the moist skin

• Most amphibians are limited to life on water’s edge or moist areas– Toads live in drier areas but still return

to water to reproduce

Amphibian diversity• Not always easily seen, but numerous worldwide

(Must complete part of life cycle in water)• Frogs & Toads (Anura) http://youtu.be/Tz1vyIavi_M

• Salamanders & Newts (Caudata) http://youtu.be/jX3TGK1Ey9w

• Caecilians (Apoda)http://youtu.be/DMvL4zOLSeM

What’s that sound?

• Acoustic communication is essential for the frog's survival– Territorial defense and in localization and attraction of

mates• Frogs can hear above and below water– Tympanic membrane (eardrum) size & distance apart is

related to frequency of calls• The call or croak a frog makes is unique to its

species, some species do not vocalize– Pass air through larynx (“voice box”) in throat, often

amplified inflated with vocal sacs – Ex. Bullfrog http://youtu.be/M02_dnl9zCA, treefrog http://youtu.be/080Dv8pV2y8 wood

frog http://youtu.be/BaTret-W7DA Spotted toad http://youtu.be/j5vGZsCP1Co

Amphibian origins• 360 mya freshwater seas filled with carnivorous fishes– Early tetrapods may have used limbs to move among

marshlands– Later fossils show ability to lift body off the ground– Ability to breathe air with lungs evolved

• Adaptations necessary to provide support to land-heavy bodies, efficient respiration, membrane protection from dryer air (prevent water loss)

• Challenges of life on land:– More O2, large food supply, shelter, no predators– But air changes temperature faster, bodies are clumsier on land

• Some early amphibians had legs at right-angles to body

• Became dominant terrestrial predators during warm, wet Carboniferous period 345 mya