Chapter 10
Marine Fishes
Karleskint
Turner
Small
Fishes and Other Vertebrates
• 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
ultimately replacing all but a few jawless
forms.
Jawless Fishes
•
•
•
•
•
Hagfish - lampreys
Lack both jaws and paired appendages
Have skeletons of cartilage (no bone)
Lack scales
Hagfish also lack vertebrae
Hagfishes
• Bottom dwelling “slime eels”
• Skins are used to make leather goods
• Slime glands produce abundant milky,
gelatinous fluid for protection if hagfish is
disturbed
Lampreys
• Have oral disk and rasping tongue covered with
horny dentacles to grasp prey, rasp hole in the
body and suck out tissue and fluid.
Cartilaginous Fishes
• Class Chondrichthyes
– e.g. sharks, skates, rays, chimaeras
• Skeleton of cartilage
• Possess jaws and paired fins
• Placoid scales cover skin
Sharks
• Top predators of ocean’s food webs
• 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
Dorsal fin
Kidney
Rectal
Spine
Stomach Testis Gill slits
gland Spleen
Caudal fin
Mouth
Clasper
Pelvic Intestine Pancreas
fin
Liver
Cloaca
Heart Pharynx
Pectoral
fin
Placoid
scales
Stepped Art
Fig. 10-3, p. 266
Sharks
• Ventral mouth with multiple rows of teeth
which are constantly replaced
• Found in all oceans with the greatest
numbers in temperate and tropical waters
• Humans exploit shark populations for fins,
meat, oil, leather, cartilage and sport
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
• Lack anal fin
• Specialized teeth are used to crush prey (e.g.
benthic invertebrates)
Skates and Rays
• 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 (nonvenomous) barbs along their pointed rostrums
• Fished commercially for food, many are considered
threatened
Lobefins
• Coelacanths – classified as lobefins due to
presence of rod-shaped bones surrounded
by thick muscle in the pelvic and pectoral
fins
• Only known as fossils until discovery of living
specimen in 1938
Lobefins
• Live in Indian Ocean at depths of 150 to 250
meters
• Skeleton made of bone and cartilage (vertebral
column is cartilage)
• Rostral organ in head detects weak electrical
currents, may aid in prey detection
• Life span is 60 years, reach sexual maturity at ~ 20
years, produce 5 to 26 live young
• Considered to be in danger of extinction
Ray-Finned Fishes
• Possess unpaired and paired fins,
providing better control of movements
• 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
The Biology of Fishes: Body Shape
• Shape of body determined by characteristics
of habitat
• Fusiform body shape: streamlined shape
with a very high and narrow tail
– efficient movement for active swimmers
Body Shape
• Laterally
compressed
or deep body
– allows
navigation
through
complex
habitat, e.g.,
grass or
corals
Body Shape
• Depressed or flattened bodies
– bottom-dwelling fishes
Body Shape
• Globular bodies, enlarged pectoral fins
– appropriate for sedentary lifestyle
Body Shape
• Long, snake-like bodies, absent or
reduced pelvic and pectoral fins
– useful for burrowing, living in tight spaces
Fish Coloration and Patterning
• Countershading is seen in open ocean fish
– when viewed from above, dark color blends in
with surrounding water; when viewed from
below, white belly blends in with lit surface
waters
• Disruptive coloration—background color of
the body is usually interrupted by vertical
lines; may be a dark dot (“eyespot”)
present in tail area
– more difficult for predators to see the fish
Fish Coloration and Patterning
• Poster colors: bright, showy color patterns
– may advertise territorial ownership, aid
foraging individuals to keep in contact, or be
important in sexual displays
– warning coloration: bright coloration to warn
predators that the fish is too venomous or
spiny to eat
Fish Coloration and Patterning
• Cryptic coloration: coloration which blends
with the environment
– used for camouflage
Locomotion
– muscles contract alternately from one side of
the body to the other
Locomotion
• 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 without
body flexure
The Biology of Fishes
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
Gill
filaments
Gill
rakers
Operculum (gill cover)
Oxygenated
blood leaving gill
Water
+
O2
Water
+
CO2
Deoxygenated
blood
entering
gill
Deoxygenated
blood entering
gill
Gill
filament
Water
and CO2
Blood
flow
Blood
capillaries
Water
and O2
Stepped Art
Fig. 10-21, p. 278
Respiration and Osmoregulation
• Water must be continuously moved past
the gills to keep blood oxygenated
– most ray-finned fishes ventilate gills by
pumping water across them using gill pumps
– very active fishes, e.g., sharks, tuna, and
swordfish use ram ventilation—continuously
swimming forward at high velocity with the
mouth open
Respiration and Osmoregulation
• Osmoregulation refers to process by which
organisms maintain proper concentration
of solutes and water in body fluids
• Blood’s salt concentration is about 1/3 that
of seawater, so water is lost
• Fish drink seawater to compensate
Water gain by osmosis
Salt-excreting
gland
Salts diffuse in
through gills
Some
salt water
swallowed
with food
Kidney with
large glomeruli—
reabsorbs urea
Large volume of
hypotonic urine
Water loss by osmosis
Drinks
salt water
Salt excreted
through gills
Gains salts
by diffusion
Small volume of
isotonic urine
Kidney with small
or no glomeruli
Stepped Art
Fig. 10-22, p. 279
The Biology of Fishes
Cardiovascular System
• Consists of heart, arteries, veins, and
capillaries
Cardiovascular System
– maintain body-core temperature at 2-10oC
above seawater, increasing efficiency of
swimming muscles
The Biology of Fishes
Buoyancy Regulation
• Maintaining buoyancy
– sharks sink if they stop swimming
– large livers produce squalene—an oily material
with a density less than seawater
Buoyancy Regulation
• Most fish use a swim bladder—a gas-filled
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
Buoyancy Regulation
• Active swimmers do not have swim
bladders, and must swim to avoid sinking
• Bottom dwelling fish lack swim bladder, do
not need to maintain buoyancy in water
column
The Biology of Fishes
Nervous System and Senses
• Nervous system consists of: brain, spinal
cord, peripheral nerves, and various sensory
receptors
• Olfaction and Taste
– olfactory receptors in sharks (“swimming noses”)
well developed
– ray-finned fishes have olfactory pits—blind sacs
opening to the external environment that contain
olfactory receptors
– taste receptors may be located on the surface of
the head, jaws, tongue, mouth and barbels
(whisker-like processes about the mouth)
Nervous System and Senses
• Lateral line system and hearing
– ray-finned fishes have a lateral line system for
detecting movement in the water – aids in
locating prey and avoiding predators
– lateral lines consist of canals running along
the length of the fish’s body and over the head
Nervous System and Senses
• Lateral line system and hearing
– ears are internal and have a detection range
of 200 to 13,000 hertz
• human range = 20 to 20,000 hertz
Nervous System and Senses
• Vision
– no eyelids (or poorly developed)
– usually don’t need to adjust pupil size
because of the low quantity of light
– eyes are usually set on the sides of the head
– shallow-water species can perceive color
Nervous System and Senses
• Ampullae of Lorenzini
– organs scattered over the top and sides of
shark (and relatives) head
– sense electrical currents in water
The Biology of Fishes: Digestion
• Digestive system consists of mouth,
pharynx, esophagus, stomach and
intestine
Digestion
• All cartilaginous fish are carnivores
• Ray-finned fishes exploit all food resources
and can be carnivores, herbivores or
omnivores
• Prey of carnivorous fish is swallowed whole,
chewing would block water flow past gills
• Filter feeding fish (e.g., basking sharks) use
gill rakers to filter plankton
The Biology of Fishes
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
• Parrotfish secrete a mucus cocoon
• Surgeonfish are armed with razor-sharp
spines
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
The Biology of Fishes: Reproduction
• Sexes are typically separate
• Sperm and eggs pass to the outside through
ducts
Reproduction
• Three reproductive modes:
• Oviparity – eggs are shed into the water column
and embryo develops outside the mother’s body
– common in ray-finned fishes
• Ovoviviparity – fertilization is internal and eggs
hatch within mother’s uterus, where they are
nourished by yolk stored in egg
– common in sharks
• Viviparity – young attach directly to mother’s
uterine wall or uterus produces “uterine milk” that is
absorbed by embryo
– occurs in some sharks and some ray-finned fishes
Reproductive Strategies
• 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
The Biology of Fishes: Schooling
• School of fish = group of individuals that
operates in a polarized, synchronized
fashion
• Reasons for schooling:
- more eyes increases food finding abilities and
predator avoidance
- predators can’t focus on an individual
The Biology of Fishes: 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 to
spawn