Our first focus…FISH

In your own words, describe what makes a fish a fish.

What Is A Fish?Definition: aquatic

vertebrates that are characterized by scales, fins, and gills

Have a cranium (skull)

Lack limbs or digits

Types of Fish3 main groups of

fishes:Jawless fish

Ex: hagfish

Cartilaginous fish Ex: sharks

Bony fish Ex: puffer fish

Thinking about the three types of fish, draw a cladogram with how they could be classified. Explain why you chose it.

Evolution of FishesJawless fishes with heavy

armor (bony plates)Then came the fishes

with jaws (an important evolutionary innovation!)

Then came paired appendages (pectoral and pelvic fins)

Then came the cartilaginous and bony fishes

Jawless Fish (Agnatha)Lampreys

Filter feeders as larvae, parasites as adults

Head is a round sucking disk with a mouth in the middle

HagfishWorm-like bodies with 4-6

short tentacles around the mouth

Only a light-detecting region, no eyes

They use a toothed tongue to scrape holes into dead or dying fish for food

They secrete tons of slime

http://www.youtube.com/watch?v=bqk0mnMgwUQ

Cartilaginous Fish (Chondricthyes)

Chondros means cartilage, icthyes means fishToothlike projections all over their cartilaginous

skin (act like scales and aide in swimming)Multiple rows of teethA typical shark may go through 20,000 teeth in

one lifetime!

Bony Fishes (Osteichthyes)~40% of all vertebrates are bony fishes

What are the 3 big questions we want to think about for every group of animals we are going to be discussing.

How do they Reproduce?Most are oviparous (egg layers)

with external fertilizationSome have internal fertilization

and lay fertile eggs (sharks)Varied parental care (from non-

existent to utmost importance)Some fish are ovoviviparous

(young develop inside the mother’s body but are not nourished directly by the mother’s body)

Still others are viviparous (species that bear living young and have unborn young that are nourished directly by the mother’s body)

How do they eat: FeedingVariety of feeding

mechanismsHerbivorescarnivores parasitesfilter feedersdetritus feeders

Many fish do more than one

DigestionFood goes from the mouth to the esophagus,

to the stomach where it is broken downIn some fish, the broken down food can go to

fingerlike pouches at the point where the stomach and the intestines meet called pyloric ceca

Any other undigested food gets passed through the anus as waste

ExcretionFish excrete nitrogenous waste in the form

of ammonia through gills and kidneysOsmoregulation:

Freshwater fish

Saltwater fish

How do they Survive:Respiration

Most breathe with gills

Gills contain many capillaries, allowing for maximum exchange of O2 and CO2

Dissolved gasses are sometimes stored in a swim bladder, a sac that lies on top of the body cavity and is used for buoyancy

How do they survive:Internal Transport

Closed circulatory systemTwo-chambered heart (atrium, ventricle)

ExExplain how blood and gas exchange within a fishes circulatory system.

How do they Survive:Response

Well-developed nervous system organized around a brain

Spinal cord (hollow dorsal nerve cord) lies behind the brain and may be protected by a vertebral column

Chemoreceptors and electrical detectors may aid in strong sensory perception in some fish