Reading Assignment:

• Chapter 12--Systematics, genetics, and speciation

basking shark

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Freshwater vs. Saltwater

• 58 % of fishes are marine• 41 % freshwater• Earth’s waters:

– 97% saltwater; 70% of surface of Earth– 0.0093 % freshwater; 1% of Earth surface

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Diversity of Life Styles:

• nekton (self mobile) • plankton (drifters) • bottom dwellers

(benthic)• open water (pelagic) • surface oriented

(epipelagic)

• carnivorous• omnivorous• herbivorous• filter feeders• parasites• diadromous

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Fish Diversity

Phylum

Subphylum

Superclass

Class Chondrichthyes ActinopterygiiCephalaspidomorphiMyxini

Gnathostomata (jaws)

hagfish lampreys cartilaginous fishessharks, skates, rays

ray-finned fishes

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Chordata

Craniatata (cranium)

other verts?

Why do we recognize fish?

• Constraints & Characteristics of water– density (800 x denser than air)– support (lighter skeleton, diminished limbs)– viscosity (streamlined shapes)

• Evolutionary convergence • Absence of divergence

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Thoughts on the Evolution of Fishes

• What are general characteristics of fishes and vertebrates? (consider their protist and invertebrate ancestors)

• size• locomotion• bilateral symmetry

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Advantages of size:

• Survivability:predator avoidanceprey availabilityenvironmental selection and avoidance

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Requirements for size:

• support (skeletal system)• mechanisms of locomotion• systems

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Simplest form of locomotion in cordates

Direction of locomotion

Notochord--flexible, incompress.

sinusoidal movementend

Vertebral column:

vertebrae discs

Flexibleincompressible

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Caudal fin

Pectoral fins Pelvic fins Anal fin

Dorsal fin--raysDorsal fin--spines

Caudal peduncle

end

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Physical Aspects of Aquatic Environments

H H

OWater:

104.5

covalent bond

-

+ polar molecule

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Water is a polar molecule

• dissolves polar substances--salts, etc• doesn’t dissolve non-polar substances--fats,

oils, waxes

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oil

Soap molecule:

polar

non-polar

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Ionization of water:

2H2O H3O+ + OH-

hydronium ion hydroxide ion

H+ H+ . H2O

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How much does water ionize?Hint: pH = -log H+

10log 10-7 g-ions/l

0.0000001 g-ions/lNote: inverse log scale

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Many other substances ionize in water:

Salts: NaCl Na+ Cl-+

Bases: NH3 + H2O NH4+ OH-+

Acids: H2CO3 H+ HCO3-+

carbonic acid

ammonia

bicarbonate

ammonium

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Density of water

H HO

OHH

OHH

H HO

HHO

Ice: voids

voids

voids

Covalent bond-share electrons Hydrogen bond-electrostaticend

As temp of ice increases:

• Molecules vibrate more rapidly• hydrogen bonds begin to break• free molecules fill voids• water becomes densest• vibrations increase in amplitude;

intermolecular distances increase

TEMP.

0 °C

3.94 °C

100 °C

Densityg/ml

Ice - 0.917water - 0.9999

1.000

0.996

Significance with respect to life?end

Density of water increases slightly with salinity

salinity

dens

ity

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Stratification:

epilimnion

hypolimnion

thermocline

less dense

more dense

end

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Semester Projects

• 100 point project• usually library research leading to a written

paper• do some preliminary research to define

topic• have topics approved by September 30• Project due at end of semester

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Engineer a new species:

• Given a certain biomass to work with, how big would you make them? Why?– Considerations related to size

• extremes• survivability versus cost of losing an individual

• What other characteristics would you choose? Why?– locomotion?, symmetry?, survivability?

Thought experiment:

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Evolutionary race among predators and prey:

size locomotion

bilateral symmetryguidance

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