Download Ch 41 Fishes

Chapter 41 - Fishes
• 41-1 Introduction to Vertebrates
• Phylum: Chordata
– Subphylum Vertebrata
• Like all chordates have the 4 required
characteristics
– Notochord, dorsal nerve cord, pharyngeal pouches,
postanal tail
• 3 distinguishing characteristics
– Vertebral column
– Cranium
– endoskeleton composed of bone or cartilage
Classification
• More than 45,000 species that occupy many
different habitats
• Major groups of vertebrates
– Class Agnatha: Lamphreys and Hagfishes
– Class Chondrichthyes: Sharks, Rays, Skates
– Class Osteichthyes: Bony Fishes (ex: salmon, catfish)
– Class Amphibia: Amphibians (ex: frogs, salamanders)
– Class Reptilia: Reptiles (ex: turtles, lizards, snakes)
– Class Aves: Birds
– Class Mammalia: Mammals
Evolution
• Most biologists think vertebrates originated about
550 mya
– Oldest know fossils are of jawless fish
•
•
•
•
Most did not have paired fins
Bodies covered with heavy, bony scales
Skeleton made of cartilage
Diversified into many evolutionary lines
• Origin of Jaws
– First fish w/ jaws and paired fins appeared 440 mya
• Seize and manipulate prey, increased stability and
maneuverability
– Jaws probably evolved from the first pair of gill arches
41-2 Jawless Fishes, Sharks, and Rays
• The term fish refers to 3 distinct classes
• Life in the water
– Body plan of fish is well adapted
•
•
•
•
•
•
Streamlined shape, muscular tail
Paired fins: allow maneuverability
Unpaired fins: increase stability
Most tissues are denser than water
Can control amount of gas (regulate vertical position)
Use gills for gas exchange
– Scales limit diffusion
• Lateral Line System: row of sensory structures that run the
length of the fish’s body
Homeostasis
• Gain/lose water through osmosis
– Based on salt content of environment
• Kidneys and gills play a large part in ridding body
of waste products
Class Agnatha
• Jawless fish: Hagfishes and Lampreys
• Eel-like body, cartilaginous skeleton, unpaired
fins
• Notochord remains throughout life
Hagfishes
• Small eyes that are beneath the skin
• Bottom dwellers in cold marine
waters
• No jaws, so they feed by sawing the
fish with its toothed tongue
– Often burrow into body of dead fish
and eat from the inside out
• Evade capture by tying in knots or
secreting bad tasting slime
• When not feeding they remain
hidden in burrows
Lampreys
• Have large eyes
• Live in both freshwater
and marine environment
– Always breed in freshwater
– External fertilization
• Free living or parasitic
– Feeding: attach by suction,
tear a hole with toothy
tongue, secrete chemical to
prevent clotting
Class Chondrichthyes
•
•
•
•
•
Sharks, Skates, and Rays
Skeletons composed of cartilage
Have moveable jaws, paired fins, and skeletons
Almost all species live in salt water
Skin covered with placoid scales:
– Tooth-like spines that feel like sandpaper
– Reduce turbulence of water flow
Sharks
• Many different food sources
– Largest sharks (Whale and Basking) eat plankton
• Swim in a side-to-side motion b/c of their
asymmetric tail fins.
• Behind their heads are paired pectoral fins that jut
out of their bodies like the wings of a plane
Sharks Cont’d
• The shark’s mouth has 6 to 20 rows of backwardpointing teeth
– When a tooth breaks from front row, another moves
forward to take its place
• Amazing senses
– Nostrils have specialized nerve cells that connect with
olfactory bulbs in the brain
– Sensitive to electrical fields (think muscle contractions)
• Gas exchange requires a continuous passage of
water over a shark’s gills.
Rays and Skates
• Flattened bodies w/ paired wing-like pectoral fins
– Some have whiplike tails
• Rays: diamond or disk-shaped bodies
• Skates: Triangular bodies
• Primarily bottom dwellers
Adaptations
• Gas exchange requires a continuous flow of water
across the gills
• Do not release ammonia
– Convert to urea, raises conc. of solutes to match sea
water
• Maintain position in water
– Generates lift as it swims to counteract sinking
• Uses a lot of energy
– Store large amounts of lipids in the liver (increase
buoyancy)
Reproduction
• Internal fertilization
– Male transfers sperm into female body with modified
pelvic fins called claspers
• Some lay yolky eggs right after fertilization
• Many allow eggs to develop inside the body
– Young are born live
• No cartilaginous fish provide parental care for
young after birth
41-3 Bony Fishes
• Class Osteichthyes
– 95% of all known species of fishes
• Characterized by 3 key features
– Bone
• Harder and heavier than cartilage
– Swim bladder (or lungs)
• Gas filled sac used to control buoyancy
– Scales
• Protection and help reduce water resistance
Characteristics
• Lobe-Finned Fishes
– Have fleshy fins supported by a series of bones
– Only seven species exist today
– Ancestors of amphibians and all other terrestrial
vertebrates
• Ray-Finned Fishes
– Have fins that are supported by long, segmented,
flexible bony elements called rays
• Probably evolved from scales
• Very diverse
External Anatomy
(Yellow Perch)
• On each side of the head is the operculum
– Hard plate that protects the gills
• Fins
– Caudal fin: extends from the tail
– 2 Dorsal fins (anterior and posterior) & Anal fin
(ventral): help keep fish upright and in a straight line
– Pelvic & pectoral fins: navigate, move up and down
• Skin (scales)
– Covered in thin, round, overlapping disks
– Grow throughout life of fish
External Anatomy
Digestive System
• Generalized carnivores
• Jaws armed with many sharp teeth that point
inward to keep smaller fish and other prey
from escaping
• Food passes from mouth pharynx
esophagus stomach intestine anus
– Digestion takes place in out pockets of stomach
called pyloric ceca
– Liver and pancreas secrete digestive enzymes (bile
and insulin) that help break down food
Circulatory System
• Delivers oxygen and nutrients & transports waste
• Consists of:
– Two-chambered heart
– Blood vessels
– Blood containing red and white blood cells
• Heart pumps blood through arteries to capillaries
– Small, thin-walled vessels in the gills
– Blood picks up O2 and releases CO2
– Travels to body tissues for exchange
• Blood returns to heart through veins
The Heart
• 4 chambers in a row
• Deoxygenated blood empties into a collecting
chamber called the sinus venosus
• Moves into larger atrium: causes contraction
• Sped up blood moves into the muscular ventricle
– Main pumping chamber , driving force of circ. system
• Moves into final chamber, conus arteriosus
– Has an elastic wall, contains valves to prevent blood
from flowing back into the ventricle
Yellow Perch Heart
Respiratory System
• Large surface area of gills allows rapid gas
exchange
• Gills supported by four sets of curved pieces of
bone on each side of head
– Each has double row of thin projections called gill
filaments
– Water taken in mouth, pumped across gill filaments,
exits behind operculum
• Water flows away from head, blood toward
– Known as countercurrent flow
Excretory Systems
• Kidneys filter chemical wastes from blood
– Results in urine (contains ammonia, water, and ions)
– Carried from kidney through system of ducts to the
urinary bladder
• Stored then later expelled
Swim Bladder
• Gas bladder or swim bladder
– Thin-walled sac in abdominal cavity
– Contains mixture of oxygen, carbon dioxide, and
nitrogen obtained from bloodstream
– By regulating amount of gas in sac, fish adjust
overall density and thus move up or down in water
or hover at given depth
Nervous System
• Nervous system consists of:
– Brain in three sections: forebrain, midbrain, hindbrain
• Olfactory bulb: process information on smells
• Cerebrum: integrate sensory info from other areas of the brain
• Optic tecum: receives and processes visual, auditory, and lateral
line impulses; turns body toward/away from stimulus
• Cerebellum: coordinates motor function
• Medulla oblongata: regulates organs; relay station for stimuli
– Spinal Cord
• Extends length of body, carries nerve impulses to and from the
brain
– Nerves that lead to and from all parts of the body
• Spinal nerves: connect spinal cord to internal organs, muscles,
sense organs
Reproduction
• Spawning behavior is very diverse
• Separate sexes
– ovaries in female = eggs; testes in male = sperm;
both released through opening just rear of anus
• External Fertilization (usually)
• High mortality rate, often lay large #s of eggs
• A few bear live young
– Female receives sperm during mating, and
fertilization is internal
– Carries eggs in body until young are born
Reproduction Cont’d