Transcript Rays - Images

Chapter 10
Fishes
© 2006 Thomson-Brooks Cole
Key Concepts
• Hagfishes and lampreys are jawless
fishes.
• Sharks, skates, and rays have
skeletons composed entirely of
cartilage.
• Sharks have streamlined bodies and
highly developed senses that help
them to be efficient predators.
• Most marine fishes have skeletons
composed primarily of bone.
© 2006 Thomson-Brooks Cole
Key Concepts
• The shape of a fish’s body is primarily
determined by the characteristics of its
environment.
• Many fishes exhibit coloration and
color patterns that help them blend in
with their environment.
• Color in fishes functions in camouflage,
species recognition, and
communication.
© 2006 Thomson-Brooks Cole
Key Concepts
• Most bony fishes have a swim bladder that
helps them maintain neutral buoyancy.
• Most marine fishes are carnivorous, but
herbivores, omnivores, and filter feeders
also exist.
• Most marine fishes are oviparous and
produce large numbers of eggs.
• Fishes such as salmon and eels migrate long
distances sometime during their life cycle.
© 2006 Thomson-Brooks Cole
Fishes
• Fishes are vertebrates—animals that
possess vertebrae, a series of bones or
cartilages that surround the spinal cord
and help support the body
• Primitive fishes lacked paired fins and
jaws
• Adaptation of jaws and paired fins
allowed fish to more efficiently obtain
food
© 2006 Thomson-Brooks Cole
Jawless Fishes
• Class Myxini (hagfish) and class
Cephalospidomorphi (lampreys)
• Lack both jaws and paired appendages
• Have skeletons of cartilage (no bone)
• Lack scales
• Hagfish also lack vertebrae (some
scientists consider them invertebrates)
© 2006 Thomson-Brooks Cole
Hagfishes
• Bottom dwelling “slime eels”
• Skins are used to make leather goods
• Hagfish feeding apparatus is composed
of two dental plates containing horny
cusps, used to grasp the prey’s flesh
– feed on live prey and scavenge
• Slime glands produce abundant milky,
gelatinous fluid if hagfish is disturbed
• Sexes are normally separate
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Lampreys
• Have oral disk and rasping tongue
covered with tooth-like keratin plates
• Reproduction
– males migrate up rivers and build nests
– females arrive and they spawn; eggs
attach to stones of the nest
– larvae are benthic filter feeders
– after 3-7 years, they metamorphose into
adults and return to the sea
© 2006 Thomson-Brooks Cole
Cartilaginous Fishes
• Class Chondrichthyes
– e.g. sharks, skates, rays, chimaeras
• Skeleton of cartilage
• Possess jaws and paired fins
• Have placoid scales
• 2 major groups:
– holocephalans (chimaeras or ratfish)
– elasmobranchs (2 body forms:
streamlined or dorsoventrally flattened)
© 2006 Thomson-Brooks Cole
Sharks
• Excellent swimmers with streamlined
bodies
– swim with powerful, sideways sweeps of
the caudal fin (tail)
– heterocercal tail—caudal fin in which the
dorsal lobe is longer than the ventral
• Males have claspers—modified pelvic
fins which transfer sperm from the
male to the female
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sharks
• Maintaining buoyancy
– sharks sink if they stop swimming
– large livers produce squalene—an oily
material with a density less than seawater
– squalene offsets the shark’s higher density
to help maintain buoyancy
© 2006 Thomson-Brooks Cole
Shark Sensory Systems
• Vision
– a clear nictitating membrane covers and
protects each lidless eye
– many species seem to have color vision
• Olfaction
– more important than vision – almost 2/3
of the shark’s brain cells are involved in
processing olfactory information
– sharks are sometimes referred to as
“swimming noses”
© 2006 Thomson-Brooks Cole
Shark Sensory Systems
• Lateral line system
– consists of canals running the length of
the animal’s body and over the head
– canals open to the outside at regular
intervals, allowing free movement of
water over the neuromasts (sensory
receptors) within
– neuromasts detect vibrations in the fluid
which alert the shark to movements in the
water, possibly made by prey animals
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Shark Sensory Systems
• Ampullae of Lorenzini
– organs scattered over the top and sides of
the animal’s head
– sense electrical currents in the water
© 2006 Thomson-Brooks Cole
Digestion in Sharks
• Blade-like, triangular teeth in the
mouth grasp prey and tear off chunks
• Food is swallowed whole (sharks
cannot move their jaws back and forth
to chew)
• Food passes through stomach to a
short intestine containing a spiral valve
– spiral valve—a structure which aids in
absorption by slowing the movement of
food and increasing the surface area
© 2006 Thomson-Brooks Cole
Osmoregulation in Sharks
• Maintain an internal solute
concentration > or = to the seawater
– retain large amounts of nitrogenous
wastes, mostly urea and trimethylamine
oxide (TMAO)
• Gills and rectal gland (a large structure
that empties into the intestine) work to
excrete excess sodium chloride
• Kidney excretes other salts
© 2006 Thomson-Brooks Cole
Reproduction in Sharks
• Sperm produced in paired testes are
transferred to the female through
grooves in the claspers
• Oviparity
– most primitive mode
– eggs are laid outside the body and the
embryos develop in a protective case
– e.g. whale sharks, bullhead sharks
© 2006 Thomson-Brooks Cole
Reproduction in Sharks
• Ovoviviparity
– most common mode
– eggs hatch within the mother’s uterus but
no placental connection is formed
• young are nourished by yolk from the egg
– e.g. basking sharks, thresher sharks, saw
sharks, sand tiger
© 2006 Thomson-Brooks Cole
Reproduction in Sharks
• Viviparity
– most recent mode to evolve
– either the young directly attach to the
mother’s uterine wall or the mother’s
uterus produces “uterine milk” that is
absorbed by the embryo
– e.g. requiem sharks, hammerhead sharks
© 2006 Thomson-Brooks Cole
Skates and Rays
• Have flattened bodies adapted to a
bottom existence
• Greatly enlarged pectoral fins that
attach to the head
• Reduced dorsal and caudal fins
• Eyes and spiracles (openings for the
passage of water) on top of the head
• Gill slits on the ventral side
• Specialized pavement-like teeth are
used to crush prey (e.g. invertebrates)
© 2006 Thomson-Brooks Cole
Differences between Skates
and Rays
Rays: swim by moving Skates: create a wave
fins up and down
from the forward to
backward fin edges
streamlined tails with fleshier tails with small
venomous barbs or
fins and no spines
spines
larger size
smaller size
ovoviviparous
mostly oviparous
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Defense Mechanisms
• Electric rays have electric organs that
can deliver up to 220 V
• Stingrays have hollow barbs connected
to poison glands
– treatment for stingray wounds: submerge
in hot water to break down protein toxin
• Sawfishes and guitarfishes have a
series of (non-venomous) barbs along
their pointed rostrums
© 2006 Thomson-Brooks Cole
Chimaeras
• Subclass Holocephali
– e.g. ratfish, rabbitfish, spookfish
• Large pointed heads and long, slender
tails
• Gills covered by operculum; water
inhaled through the nostrils
• Males have claspers on their heads and
pelvic fins
© 2006 Thomson-Brooks Cole
Chimaeras
• Oviparous – produce large eggs in a
leathery case
• Have flat plates for crushing prey
instead of teeth
• Generally bottom dwellers
• Little commercial value
– marketed as food in parts of China and
New Zealand
– their oils can be used as a lubricant
© 2006 Thomson-Brooks Cole
Bony Fishes
• Class Osteichthyes
• Very diverse 25,000 species
• Most forms have: swim bladder (or
lung), bone, bony scales, and fin rays
• 2 major lineages:
– lobefins (subclass Sarcopterygii) –
coelacanths, freshwater lungfish
– ray-finned fishes (subclass Actinopterygii)
© 2006 Thomson-Brooks Cole
Coelacanths
• Characterized by lungs and lobed,
paired fins resembling tetrapod limbs
• Known from fossils only before live
specimen was discovered in 1938
• Skeletons are bone + cartilage
• Fat-filled swim bladder for buoyancy
• Nearly isotonic to seawater like sharks
• Ovoviviparous
© 2006 Thomson-Brooks Cole
Ray-Finned Fishes
• 2 major groups:
– subclass Chondrostei – primitive forms
with heterocercal tails, primarily cartilage
skeleton, ganoid scales
• ganoid scales—thick, heavy scales which give
the fish an armored appearance
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ray-Finned Fishes
– subclass Neopterygii – homocercal tails,
cycloid or ctenoid scales, more
maneuverable fins
• homocercal tails—tails with dorsal and ventral
flanges nearly equal in size; vertebral column
usually does not continue into the tail
• cycloid & ctenoid scales—scales that are
thinner and more flexible; less cumbersome
for active swimmers
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ray-Finned Fishes
• Possess unpaired median fins and
paired fins, providing better control of
movements
• Median fins consist of 1 or more dorsal
fins, caudal fin, and usually anal fin
– help maintain stability while swimming
• Paired fins consist of pectoral and
pelvic fins
– both used in steering
– pectoral fins also help to stabilize the fish
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Body Shape
• Fusiform body shape—streamlined
shape with a very high and narrow tail
– efficient movement for active swimmers
© 2006 Thomson-Brooks Cole
Body Shape
• Laterally
compressed
or deep
body
– allows
navigation
through
grass or
corals
© 2006 Thomson-Brooks Cole
Body Shape
• Depressed or flattened bodies
– bottom-dwelling fishes
© 2006 Thomson-Brooks Cole
Body Shape
• Globular bodies, enlarged pectoral fins
– appropriate for sedentary lifestyle
© 2006 Thomson-Brooks Cole
Body Shape
• Long, snake-like bodies, absent or
reduced pelvic and pectoral fins
– useful for burrowing, living in tight spaces
© 2006 Thomson-Brooks Cole
Fish Coloration
• 2 basic types of fish colors:
– pigments (biochromes)
– structural colors
• Pigments—colored compounds found in
chromatophores
– chromatophores—irregularly-shaped cells,
usually appearing as a central cell body
with radiating processes
– fish can alter color by moving pigments
between the central core and processes
© 2006 Thomson-Brooks Cole
Fish Coloration
• Structural colors—colors produced by
light reflecting from crystals located in
specialized chromatophores
– iridophores—chromatophores used to
produce structural colors
– colorless, relatively immobile crystals
produce mirror-like silver or iridescence
© 2006 Thomson-Brooks Cole
Fish Coloration
• Countershading is seen in open ocean
fish
– obliterative countershading—coloration in
which the back (dorsum) is dark green,
dark blue or gray, and the shades grauate
on the sides to the belly’s pure white
• Disruptive coloration—background
color of the body is usually interrupted
by vertical lines; may be an eyespot
– more difficult for predators to see the fish
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Fish Coloration
• Cryptic coloration—coloration which
blends with the environment
– used for camouflage
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Fish Coloration
• Poster colors—bright, showy color
patterns
– may advertise territorial ownership, aid
foraging individuals to keep in contact, or
be important in sexual displays
– aposematic (warning) coloration—bright
coloration to warn predators that the fish
is too venomous or spiny to eat
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Locomotion in Bony Fishes
• In swimming, the trunk muscles propel
the fish through the water
– trunk muscles are arranged in a series of
muscle bands
– muscles contract alternately from one side
of the body to the other
– contractions originate at the anterior end
and move toward the tail, flexing the body
and pushing against the water
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Locomotion in Bony Fishes
• Fish with different body forms swim in
different ways
– elongate fish undulate the entire body
– swift swimmers flex only the posterior
portion of the body
– other fish are somewhere in between
– fish with a dermal skeleton can only flex
the area before the caudal fin
– some fish swim using their fins alone
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Respiration and
Osmoregulation
• Gills often used to extract O2, eliminate
CO2, and aid in salt balance
– gill filaments—highly vascularized, rod-like
structures which compose the gills
– countercurrent multiplier system—blood
flows in the opposite direction from the
incoming water, maintaining a stable
gradient that favors the diffusion of O2 in
and CO2 out of the body
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Respiration and
Osmoregulation
• Water must be continuously moved
past the gills to keep blood oxygenated
– most bony fish ventilate gills by pumping
water across them
– very active fishes use ram ventilation—
continuously swimming forward at high
velocity with the mouth open
© 2006 Thomson-Brooks Cole
Respiration and
Osmoregulation
• Blood’s salt concentration is about 1/3
that of seawater, so water is lost
• Fish drink seawater to compensate
– chloride cells—specialized cells on the gills
which eliminate most of the excess salt
– kidneys and digestive tract remove other
excess salt
– marine fish excrete negligible amounts of
urine in order to retain maximum water
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Cardiovascular System
• Consists of heart, arteries, veins, and
capillaries
• Path of blood:
– deoxygenated blood collected from veins
by sinus venosus (thin-walled chamber)
– passed to atrium, then ventricle
– ventricle propels blood to gill capillaries
where it is oxygenated
– collected from gills by dorsal aorta and
passed to body via arteries and capillaries
© 2006 Thomson-Brooks Cole
Cardiovascular System
• Many active swimmers have a
countercurrent arrangement of blood
vessels
– maintains body-core temperature at 2-10o
C above seawater, increasing efficiency of
swimming muscles
– heat is transferred from arteries coming
from the body core to veins near the
outside, so that venous blood is warmed
before flowing toward the core
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Buoyancy Regulation
• Most fish use a swim bladder—a gasfilled sac that helps offset the density
of the body and regulates buoyancy
– the fish can adjust the amount of gas in
the swim bladder to maintain depth
– gas is added as the fish descends and
removed as it ascends
© 2006 Thomson-Brooks Cole
Buoyancy Regulation
• 2 methods for adjusting the amount of
gas in the swim bladder
– gulping air from the surface or spitting air
out as needed
– gas gland—a specialized gland which fills
the swim bladder from gases dissolved in
the blood
• fish with a gas gland empty gas from the swim
bladder through diffusion into the blood
• Active swimmers do not have swim
bladders, and must keep swimming
© 2006 Thomson-Brooks Cole
Nervous System and Senses
• Nervous system consists of: brain,
spinal cord, peripheral nerves, and
various sensory receptors
• Olfaction
– olfactory pits—blind sacs opening to the
external environment that contain
olfactory receptors
– size varies with dependence of fish on
olfaction
© 2006 Thomson-Brooks Cole
Nervous System and Senses
• Taste and hearing
– taste receptors may be located on the
surface of the head, jaws, tongue, mouth
and barbels (whisker-like processes about
the mouth)
– bony fishes have a lateral line system for
detecting movement in the water
– ears are internal and have a detection
range of 200 to 13,000 hertz
• human range = 20 to 20,000 hertz
© 2006 Thomson-Brooks Cole
Nervous System and Senses
• Vision
– no eyelids
– usually don’t need to adjust pupil size
because of the low quantity of light
– entire lens moves back and forth to focus
– eyes are usually set on the sides of the
head
– most have monocular vision
– shallow-water species can perceive color
© 2006 Thomson-Brooks Cole
Feeding Types
• Carnivores (e.g. pufferfish, groupers)
– most bony fishes are carnivores
– prey are usually seized, swallowed whole
• chewing would block water flow past gills
• Herbivores (e.g. surgeonfish, parrotfish)
– feed on a variety of plants and algae
– teeth often broad and flat with a sharp
edge to scrape food from surfaces
– may have gizzard-like stomach to grind
vegetable matter
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Feeding Types
• Filter feeders (e.g. anchovies, larvae)
– feed on plankton
– typically use gill rakers—projections from
the gill arches which filter phyto- and
zooplankton from seawater
– most travel in large schools, and are an
important food source for larger
carnivores
© 2006 Thomson-Brooks Cole
Adaptations to Avoid
Predation
• Many exhibit elaborate camouflage
• Pufferfishes and porcupinefish inflate
their bodies to deter predators
• Flying fishes use enlarged pectoral fins
to glide through the air and escape
• Pearlfish hide in other organisms
• Parrotfish secrete a mucus cocoon
• Surgeonfish are armed with razorsharp spines
© 2006 Thomson-Brooks Cole
Adaptations to Avoid
Predation
• Clingfishes use a sucker to attach to
rocks so predators can’t dislodge it
• Triggerfish projects spines to deter
predators or wedge itself into cracks
• Scorpionfish and stonefish have venom
glands for self-protection
© 2006 Thomson-Brooks Cole
Reproduction in Bony Fishes
• Gonads are paired structures
suspended from the roof of the body
cavity by mesenteries (membranes)
• Sperm and eggs pass to the outside
through ducts, except in salmon
• Egg and sperm development is usually
seasonal
• Variation in the level of pituitary and
gonadal hormones controls the
reproduction process
© 2006 Thomson-Brooks Cole
Reproduction in Bony Fishes
• Pelagic spawners (e.g. tuna, wrasses)
– release vast quantities of eggs into the
water for fertilization by males
– fertilized eggs drift with the currents
– no parental care
• Benthic spawners (e.g. smelt)
– non-buoyant eggs with large yolks
– no parental care
– pelagic or benthic embryos/larvae
© 2006 Thomson-Brooks Cole
Reproduction in Bony Fishes
• Brood hiders (e.g. grunion)
– species that hid their eggs in some way
but exhibit no parental care
• Guarders (e.g. damselfish)
– species that care for their offspring until
they hatch and, frequently, through their
larval stages
• Bearers (e.g. jawfish, seahorses)
– species that incubate their eggs until they
hatch (in the mouth or a special pouch)
© 2006 Thomson-Brooks Cole
Reproduction in Bony Fishes
• Larval development
– many larvae are zooplankton
– initially nourished by a yolk sac attached
to the abdomen; absorbed once mouth
and digestive tract have developed
– larva grows into juvenile, leaves the
planktonic community to become adult
– fishes grow for as long as they live
© 2006 Thomson-Brooks Cole
Reproduction in Bony Fishes
• Hermaphroditism—individuals have
both testes and ovaries at some time
in their lives
– occurs in at least 14 bony fish families
– synchronous—possessing functional
gonads of both sexes at one time
– sequential—changing from one sex to
another
• protogyny—changing from female to male
• protandry—changing from male to female
© 2006 Thomson-Brooks Cole
Fish Migrations
• Daily migrations usually associated with
feeding and predator avoidance
• Seasonal migrations usually associated with
spawning, changing temperatures or feeding
• Migrations may occur within seawater or
between seawater and fresh water
– catadromous—fishes that move from fresh water
to seawater to spawn
– anadromous—fishes that move from seawater to
fresh water to spawn
© 2006 Thomson-Brooks Cole
Fish Migrations
• Freshwater eels
– best-studied catadromous fishes
– migrate down coastal rivers to the sea
during the fall
– adults spawn and then die
– young hatch, develop into leaf-like
leptocephalus larvae, and migrate back to
rivers
– after arrival, young metamorphose into
juveniles (elvers) that migrate into
streams and estuaries
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Fish Migrations
• Salmon
– Atlantic/Pacific species are anadromous
– Pacific species return to spawning grounds
once, reproduce, and die; Atlantic species
may spawn more than once
– lay eggs in a redd—a shallow depression
in the gravel of a fresh water stream
– salmon navigate upstream by the
characteristic odor of the stream; there is
not agreement on how they locate the
correct river’s mouth from the open sea
© 2006 Thomson-Brooks Cole