Introduction to Fish

Phylum Chordata

Subphylum Vertebrata

– Class Agnatha– Class Chondrichthyes– Class Osteichthyes– Class Amphibia– Class Reptilia– Class Aves– Class Mammalia

fish

Class Agnatha - jawless fish: hagfish and lampreys

• absence of jaws• no paired fins• cartilaginous skeleton• 2-chambered heart

Agnatha

Jaws evolved from gill supports.

• Jaws developed from gill arches located around the pharynx.

cranium

mouth gill arches

cranium

mouth

cranium

mouth

• Jaws gave vertebrates a huge advantage as predators.

Only two groups of jawed fish still exist. • Cartilaginous fish and bony fish are still in existence.

• Cartilaginous fish have skeletons made of cartilage.

• Cartilaginous fish include the Holocephali and Elasmobranchs

– Holocephali include ratfish, a small group of deep-sea fish.

– Elasmobranchs include sharks, rays, and skates.

Class Chondrichthyes - cartilaginous fish: sharks and

rays

• cartilaginous skeleton• 2-chambered heart• 5+ pharyngeal slits• well developed lower jaw• bony teeth• placoid (tooth-like) scales• ventral mouth and nostrils• nostrils do not open into mouth

Cartilaginous fish

Chondrichthyes

Bronze whaler

Eagle ray

Chondrichthyes

Class Osteichthyes - bony fish

• ossified skeleton• 2-chambered heart• pharyngeal slits covered by single bony

operculum (gill cover)• membranous fins strengthened with rays• presence of a swim bladder (teleost)• lateral line sensory receptor

Bony fish

Swim bladder

Fish are vertebrates with gills and paired fins.

• Fish use specialized organs called gills to breathe underwater.– sheets of thick, frilly tissue filled with capillaries – take in dissolved oxygen from water, release carbon dioxide

waterflow

• Countercurrent flow is the opposite movement of water against the flow of blood in the fish’s gills.

Circulatory system of fish

• Bony fish have skeletons made of bone.

– operculum protects a bony fish’s gills– movements of operculum help bony fish move water over gills

• Fins are surfaces that project from a fish’s body.

dorsal fin

caudal fin

anal finpectoral fin pelvic fin

– keep fish stable– redirect water around fish as it swims– help fish maneuver in water

•Myomeres – bands of muscle along sides of body contract pushing against water, forces body forward

•Dorsal & anal fins – act as rudders to steer & provide stability (unpaired)

•Pelvic fins – to turn, balance, & “brake” (paired)

● Pectoral fins – steering (paired)

Fish senses

• All fish have a lateral line system.

– sensory system– sensitive to small changes in water movement

lateral line

Lateral line system

Fish scales

• Reduce drag and direct water flow

Types of fish scales

General Life Style Categoriesa. pelagic cruisers1. occurring in water column far away from the bottom (benthic)

environment2. often referred to as "blue water"3. includes tuna, billfish, blue sharks, mackerel sharks (great

whites and mako sharks)

Fish Adaptations and Life Styles

b. demersal1. bottom-associated fishes, but not usually sitting on the bottom

2. rely on the benthic environment as a source of food, place to reproduce, and/or place of refuge, etc.

3. includes most reef fishes (e.g., butterfly fishes, surgeon fishes, wrasses, parrot fishes, etc.)

c. benthic1. bottom-dwelling fishes that spend the majority of time

sitting on the bottom

2. includes flatfishes, lizard fishes, many scorpion fishes, many hawkfishes, gobies, etc.

tuna

1) fusiforma) = torpedo-shaped b) allows minimal drag while swimmingc) best shape for a pelagic cruise

Body shape

2) compresseda) laterally flattened (e.g., butterflyfishes &

surgeonfishes)b) allows for maneuverability in surge environmentsc) useful for demersal fishes that hover above the reefd) exception seen in flatfishes that lie on one side of the

body as benthic fishes

John Dory: predator in waiting…

3) elongated or attenuateda) long body (e.g., trumpetfish, cornetfish, eels)b) seen in demersal fish that either hover

motionless in the water)c) seen also in benthic fishes (e.g., eels) that

hide in holes in the reef

4) depresseda) dorso-ventrally flattened (e.g., frogfishes,

scorpionfishes & gobies)b) broad ventral surface facilitates resting on

the bottomc) seen in many benthic fishes

Body Coloration

1) source of colora) pigment color - chromatophores for yellows,

reds, oranges, browns, & blacksb) structural color - iridophores (reflection) &

light refraction for blues, silvers, & rainbows

2) patterns

a) countershading

1) dark blue or black dorsally, white or silvery ventrally

2) results in blue water "camouflage“

3) observed most frequently in pelagic cruisers

b) camouflage1) matching the background coloration2) usually involves having irregular dark

blotches and spots3) typically seen in benthic fishes, especially

benthic ambush predators (e.g., frogfishes, gobies, & many scorpionfishes)

4) some fishes (e.g., flatfishes) may exhibit rapid color changes in response to different backgrounds

Cryptic colouration

b) camouflage

5) matching downwelling light

Cookie cutter shark

Hatchet fish

c) disruptive coloration

1) color pattern breaks up the silhouette of the fish

2) may involve dark bars across the eye and tail region

3) seen in many demersal fishes such as butterfly fishes

d) bars and stripes1) bars are vertical (e.g., manini)2) stripes are horizontal (e.g., ta'ape)3) seen frequently in schooling demersal

fishes4) may confuse potential predators by making it difficult to select individual

prey from the school

e) misdirection

1) false eye spots, etc.2) observed in many demersal butterfly fishes

f) advertising coloration1) bright, obvious color patterns2) possible functions

a) advertising a cleaning station (e.g., cleaner wrasses)b) advertising a warning (e.g., nohu)c) advertising for mates (e.g., male

parrotfishes)

Hawaiian cleaner wrasse Nohu

g) mimicry1) imitating other creatures2) seen in a few demersal and benthic fishes3) examples

a) blenny (Aspidontus taeniatus) mimics cleaner wrasses

b) shortnose wrasse mimics Potter's angel which sports a defensive spine

g) mimicry4) leafy sea dragon (Australia)

h) uniform red coloration

1) most often observed in deep-dwelling or night active demersal fishes

2) examples include opakapaka, oweoweo, menpachi, & squirrelfishes

i) noctural versus diurnal color changes

j) male versus female color differences

k) juvenile versus adult color differences

Bluehead wrasse

Dragon wrasse

Stoplight parrotfish

Sex and social behaviour

Territoriality

Black angel fish

Placoderm(395-345)

lamprey & hagfish

Ost

raco

derm

(510

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Ost

eich

thye

s (3

95)

Chondrichthyes (370)

(360)

                                                                                                                    

Coelacanth

Lungfish

New Zealand Fish

• Over 1,000 species, many in Indo-Pacific and Australia as well

• Of the 270 coastal species, approx. 25% are endemic

Triplefins

Osteichthyes

Parore: Herbiverous fish feeding on kelps and other algae

• Demersal fish live on the sea floor

• Pelagic fish live in the water column above

Variations on a theme

Osteichthyes

Blue maomao : plankton feeders

Trevalley : plankton feeders

Snapper

Leatherjacket

Yellow-finned tuna