What is a Fish?• Fishes are aquatic vertebrates. Most fishes

have paired fins, scales, and gills.

Feeding and Digestion• Every mode of feeding is seen in fish –

herbivores, carnivores, parasites, filter feeders, and detritivores

Feeding and Digestion continued

• Complete Digestive Tract

– Food passes through the mouth and esophagus to stomach where digestion begins

Feeding and Digestion continued

• The pyloric ceca (cecum - singular)(fingerlike pouches) secretes digestive enzymes and absorbs nutrients from the digested food

Feeding and Digestion continued

• The liver secretes bile which helps break down fat

• The pancreas releases digestive enzymes into intestine

• The gallbladder stores bile and releases it to the intestine Gallbladder

• These are accessory organs, NOT part of the digestive tract

Feeding and Digestion continued

• The intestine completes the process of digestion and nutrient absorption

Feeding and Digestion continued

• Undigested material is eliminated through the anus

• Digestive Tract: M>E>S>I>A (write the words out) Accessory organs are not included.

Respiration• Most fishes exchanges gases with gills located

on either side of the pharynx

• Oxygen-rich water moves into the mouth and is pumped over gill filaments

• Oxygen-poor water is pushed out through openings in the sides of the pharynx

Circulation• Closed system – consists of heart, blood

vessels, and blood (duh)

• Delivers oxygen and nutrients to body cells

• Single-loop

– Heart pumps blood to gills where it picks up oxygen and releases carbon dioxide

– Blood moves to all body tissues then back to heart through veins

Circulation continued

• Most Fish hearts have 4 parts:

– Sinus venosus

– Atrium

– Ventricle

– Bulbus arteriosis

Sinus Venosus Atrium

VentricleBulbus arteriosus

Circulation continued

• Oxygen-poor blood from the veins collects in the sinus venosus

• Blood enters the atrium (one-way compartment) and flows to the ventricle

• The ventricle pumps blood into the bulbusarteriosus

• The bulbus arteriosus moves blood into the ventral aorta and toward the gills

Excretion• Kidneys filter chemical wastes from the blood

• Urine is formed in the kidneys and carried to urinary bladder where it is stored and later expelled

Urinary bladder

Excretion continued

• Kidneys help maintain homeostasis by varying the amount of water and salts in urine

– Saltwater fish – excrete very little urine but it is highly concentrated (little water)

– Freshwater fish – excrete large amounts of diluted urine (a lot of water)

Response/Nervous• Fishes have well-developed nervous systems

organized around a brain

Response/Nervous continued

• The olfactory bulbs are involved with the sense of smell

• The cerebrum is responsible for the voluntary activities of the body – primarily processes sense of smell

• The optic lobes process information from the eyes

Optic lobe

Cerebrum

Response/Nervous continued

• The cerebellumcoordinates body movements

• The medulla oblongatacontrols the functioning of many internal organs

Cerebellum

Response/Nervous continued

• Most have well-developed eyes and good color vision

• Good sense of taste and smell; may not hear sounds well

• Lateral line system allows fishes to sense vibrations in the water

• Some fishes can detect low levels of electric current

Movement• Most fishes move by contracting paired sets of

muscles on either side of backbone

• Force and action of the fins propel fish forward

• Fins are used to keep on course and adjust direction

Reproduction • Separate sexes; most show external fertilization

• Spawning (reproductive behavior) varies among different species

• Most lay large numbers of eggs to ensure some will be fertilized and survive

• Most fish are oviparous (lay eggs that hatch outside of body) ex. salmon

• Some species are ovoviviparous (eggs stay in mother’s body after internal fertilization) ex. guppies

• Some species are viviparous (give birth to live young) ex. sharks

Taxonomic Classification of Fishes

• Kingdom Animalia

• Phylum Chordata

• Subphylum Vertebrata

–Class Agnatha – jawless fishes

–Class Chondrichthyes – cartilaginous fishes

–Class Osteichthyes – bony fishes

Class Agnatha• “without jaws”

• Most primitive class of fish

• Lack jaws, paired fins, and scales

• Skeleton is made of cartilage

• Retains notochord as adults

• External fertilization

• Only has 2 living members: hagfish and lamprey

Hagfish

• Body Plan:

– Pinkish-grey

– wormlike bodies

– 4 or 6 short tentacles around mouths

• Found only in oceans (bottom dwellers)

• Detritivores – use a toothed tongue to scrape a hole in the dead or dying fish’s side

• Lack eyes but they have light-detecting sensors scattered around their bodies

Lamprey• Found in fresh

water and salt water

• Feeding

– Filter feeders as larvae

–Parasites as adults - suck up tissues and body fluids of hosts

• They have small eyes beneath skin

Class Chondrichthyes• “cartilage fish”

• Sharks, skates, rays

• Have jaws, paired fins, and cartilage skeleton

• Most are covered with placoid scales – feels like sandpaper

• Almost all live in saltwater

• Diverse feeding methods – most are carnivores; some are detritivores or filter-feeders

Skates and Rays• Flat body with paired pectoral fins behind heads

• Flat shape and coloration provide camouflage

• Mainly bottom dwellers

• Feed primarily on mollusks and crustaceans

• Largest rays are filter-feeders

Sharks• Teeth are replaced throughout their lives

–Go through as many as 20,000 in a lifetime

• Use several senses to locate prey

– Smell chemicals in the water

– Sharp vision in little light

–Well-developed lateral line system detects vibrations in water

• Most are carnivores, but larger species filter-feed

• Do not have swim bladders to control buoyancy (floating)

–Must keep moving (requires a lot of energy) OR

– Store lipids in liver to reduce density and provide buoyancy

• Internal fertilization

–Male uses claspers (modified pelvic fins) to transfer sperm to female

–Most are oviparous but some are ovoviviparous or viviparous

Sharks continued

Class Osteichthyes• “bony fish”

• Catfish, salmon, perch, bass

• Have jaws, paired fins, and skeletons of bone

• 3 key features

– Skeleton of bone – harder and heavier than cartilage

– Swim bladder – used to control buoyancy

– Scales – cover most bony fish; protects and helps reduce friction

• Largest class of fish (also largest class of vertebrates)

2 Groups of Bony Fish• Lobe-finned

– Fins are fleshy (like earlobes)

–Only 7 species exist today

– Includes lungfish

2 Groups of Bony Fish• Ray-finned

– Fins are supported by long, flexible bony structures (rays)

– Very diverse group

– Includes most familiar fish – eel, perch, bass, salmon

External Anatomy• Operculum – covers and protects gills

• Fins – increase stability and movement through water– Caudal fin (tail) – moves from side to side – helps

swim

– 2 dorsal fins and anal fin – keep fish upright and moving in straight line

– Pelvic and pectoral fins – used to navigate, stop, move up and down

• Skin – Most are covered with scales – minimize friction as

they swim

– Scales grow throughout life