A)
The Pelagic Environment
1) Pelagic zone – the open ocean
a) The pelagic zone is sub divided into 5 zones based ocean depth
(i) Epipelagic (phytic zone)- thinnest layer of the pelagic zone that has enough light for photosynthisus
(ii) The Mesopelagic Zone - division of the Pelagic zone that has light, though the light is too dim to
perform photosynthesis
 The Mesopelagic Zone is also called the twilight zone because of the limited amount of light
(iii) Bathypelagic- area of open water that is completely dark
(iv) Abyssopelagic zone – area of water closest to ocen foor that is completely dark
(v) Hadopelagic zone - of the pelagic zone that consists of the deep water in ocean trenches.
B) Adaptations for living in the pelagic zone
1) There are a number of difficulties that come along with living in the pelagic zone:
a) Staying above the ocean floor
b) Getting food and avoiding predators
c) Finding mates
2) Depending on whether a fish lives in the epipelagic zone of the deep ocean, the way it overcomes these
difficulties differs
C) Staying above the ocean floor in the epipelagic zone
1) There are 2 ways organisms can help themselves float in the ocean
a) Increase water resistance
b) Increase buoyancy
2) Increasing water resistance
a) The more drag an organism has the slower it sinks
(I) This can be demonstrated by dropping a balled up piece of paper and a flat one at the same time
b) Organisms like plankton and jellyfish have flattened body shapes and many projections that help increase
their drag in the water and sink slower
3) Increasing buoyancy in the epipelagic zone
a) One common way epipelagic animals increase their body’s buoyancy is by producing and storing lipids (fats
and oils)
(I) Marine mammals produce blubber
(II) Sharks have large livers that produce large amounts of fish oil
b) Air pockets are another way organisms increase their buoyancy
(I) The three gas containing structures most commonly used in the epipelagic zone are:
(i) Rigid gas chambers
(ii) Gas floats
(iii) Swim bladders
c) Rigid gas chambers –a primitive, inflexible, shell like structure that helps some organisms remain buoyant in
the water
(I) Organisms that contain gas chambers are live mostly at a narrow range of depths because they can’t
inflate or deflate these organs easily
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(II) If the organisms go into deep or shallow water too fast the volume gas inside these structures decreases
or increases too rapidly and cracks the “shell”
(III) Nautilus and cuttlefish have these structures
(i) In cuttlefish the rigid gas chamber known as a “cuttlebone” is harvested from dead organisms and
used as calcium supplement for pet birds
d) Gas floats
(I) Some jellyfish like organisms have developed gas like sails that keep them on the surface of the water,
and help them move by being blown by the wind
(i) The by the wind sailor and Portuguese-man-of-war are two organism that developed these gas
floats
(ii) These organisms cant inflate or deflate their floats either so they are limetid to living on or just
below the serface
e) Swim bladder – a gas filled organ that can inflate or deflate to help a fish remain buoyant in water
(I) Gasses are added and removed through the blood and gills but this process may take time so any rapid
change in pressure could cause the swim batter to burst
(II) Fast moving fish, as well as Sharks and other cartilaginous fish do not have a swim blather or any main
flotation organ because they are strong enough to swim continuously in order to stay above the ocean
floor.
D) Staying above the ocean floor in the deep ocean
1) How deep water fish stay above the ocean floor depends largely on whether or not they vertically migrate
2) Deep water fish that don’t migrate vertically lack a swimbadder completely because filling it at such a pressure
would take too much energy
a) Instead they increased their buoyancy by loosing heavy defensive structures like spines and scales, and
developed soft week bones
3) Deepwater fish that do vertically migrate are not unlike epipelagic fish with well developed bones, muscles and
swim bladders that help them make the trip
a) They can rapidly fill or deflate there bladder to help deal with the pressure change, or fill their badder with
oil that doesn’t change volume with pressure
E) Getting food and avoiding predators in the epipelagic zone
1) Because there is so much light, many epipelagic organisms depend hevily on large eyes and a good sense of sight
to help find prey and avoid predators
2) Other sense organs like lateral lines, echolocation, and a good sense of hearing help some fish find prey and
avoid predators
3) Because there is few if any places to hide in the open ocean many epipelagic organisms have evolved protective
coloration to camouflage themselves in open water
a) Jellyfish and zooplankton are often completely or nearly transparent which helps them appear invisible to
predators
b) Countershading - fish that are dark on the top and light on the bottom that help them camouflage against
the water’s surface or deep water
(I) When predators look up at countershaded fish their light bottom blends with the bright ocean surface
(II) When predators look down at countershaded fish their dark top blends with the deep water
4) The ability to swim and be mobile also plays a role in a fishes ability to get food and avoid predators
a) Streamlined and compact body shapes and covering of mucus to help them slide through water
b) Stiff spines in there fins help epipelagic fish maneuver at high speed
c) They also have well developed muscle to propel there body’s through the water
(I) Red mussel in fish contains more myoglobin, a protein that stores oxygen in the tissues, which helps in
long sustained swimming
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(II) White muscle tissue fatigues rapidly but it provides more power in short bursts that red muscle can.
F) Getting food and avoiding predators in the deep ocean
1) Manny deep water fish have large highly evolved eyes that help them see in the dark
a) Some deep sea fish have tubular eyes (eyes with 2 retinas instead of one) that allow them to see not only
upward, but also to the sides and below as well in near darkness
2) Because food is so scarce Most deep water fish have large mouths and expandable stomachs that can make sure
every meal that comes along is able to be consumed
3) bioluminescent and counterillumination
a) Counteriluminationn- the ability of some organisms to produce light through cells on the bellies called
photophores that helps them blend in with background light filtering down from the surface
(I) The photophores control counterillumination can change color and intensity of light to perfectly mach
every type of light that hits the organism
b) Some deep sea shrimp secrete glowing material that flashes and distracts their predators, or sticks to them
making a surprise attach impossible
c) Bioluminescent organs around the eyes or mouth may help find or attract prey
(I) The rattrap fish has 2 glowing red spots below its eyes like headlights that allow it to illuminate prey
without being seen (no very few other deep sea organisms can see red)
d) Deep sea fish that are blind are not bioluminescent. This is a strong indication that the main function of
vision in the deep ocean is to see bioluminescent
e) Many of the enzymes that control metabolism of epipelagic fish would stop functioning under the pressures
seen in the deep ocean.
(I) To counteract this, deep sea fish have pressure resistant enzymes and high concentrations of chemicals
whose purpose is to stabilize these enzymes
G) Finding mates in the epipelagic zone
1) One way fish find mates is by Schooling
a) There is no one reason fish school
b) Mating, protection from predators, finding food, and swimming efficiency all have been shown to be
possible reasons why fish school
c) Some schools of fish are stationary while others are migratory
(I) Anadromous fish - migratory schools of fish that swim from salt water to fresh water to spawn
(i) Salmon, sturgeons, smelts, and lampreys are all anadromous fish
(II) Catadromous fish – migratory schools of fish that swim from fresh water to salt water to spawn
(i) Freshwater eels, freshwater mullets are catadromous fish
2) Hermafradism is another way fish insure that mating is successful
a) Simultaneous hermaphrodites – the ability to produce sperm and eggs at the same time
(I) Although Simultaneous hermaphrodites can fertilize there own eggs, they often opt to reproduce with
each others, taking turns acting as both the male and female in copulation
(II) Some sea basses and hamlet fish are simultaneous hermaphrodites
b) Sequential hermaphrodites (sexual reversal)– the ability of male fish to change into females (protandry) or
female fish to change into males (protogyny)
(I) Sea basses, clown fish, groupers, parrot fish, and wrasses are sequential hermaphrodites
3) Some marine organisms fertilize their eggs internally
a) Sharks and marine mammals most often fertilize internally
b) Male sharks have claspers that they use to insert into the female in order to better help the perm reach the
egg
4) Most marine organisms fertilize eggs externally
a) Broadcast spawning- Releasing large amounts of sperm and eggs into the water column
5) Once fertilized the eggs are brought to term one of three ways:
a) Oviparous- organisms that release eggs into the water column
(I) Most boney fish and some sharks (43%), and all marine reptiles and birds are oviparous
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b) Ovoviviparous – an animal the produces eggs that hatch inside the female immediately before giving birth
to live young
(I) Some sharks, like the whale shark and sand tiger shark are ovoviviparous
c) Viviparous- animals who nourish there embryo through placenta and give birth to live young
(I) Surfperch, some sharks and rays, and all marine mammals are viviparous
6) Just recently, one species of hammerhead shark was discovered to be able to give birth without its egg
becoming fertilized
a) Parthenogenesis - The development of an egg into an embryo without fertalisation by a sperm cell
H) Finding mates in the deep ocean
1) There are three main strategies deep sea fish use to find mates in the deep ocean
(I) Attraction through Bioluminescence and pheromones
(i) The light given off by some species of deep sea fish differs according to sex
(ii) Some deep sea fish have evolved a highly sensitive sense of smell that can depict pheromones given
off by females at a very low level
(II) Hermaphrodites- the ability of an organism to produce both egg and sperm
(i) some deep sea fish have the ability to produce both eggs and sperm eliminating the need to find a
mate
(III) Male Parasitism – the permanent attachment of a male to a female in some deep sea fish
(i) Once the male locates the female he bits a hole through her side and becomes permanently fused,
providing her with a constant and ready supply of sperm whenever her eggs develop
Section 2:
Biology of Fish and Sharks
A) The fish of the ocean
1) Ichthyology (ik-thi-ol-a-jee) – the study of fish
2) In general fish in the ocean can be divided into two general groups Cartilaginous fishes, and bony fishes
(I) Cartilaginous fishes – animals like sharks skates and rays and ratfish’s who belong to the Chondrichthyes
(chon-drich-theese) class of organisms
(i) These organisms have a skeleton made of cartilage which is a material that is lighter and more flexible
than bone
(ii) There mouth is below there head
(iii) They have numerous rows of well developed teeth
(iv) They have rough sand paper like scales instead of fins
(II) Bony fishes – the great majority of fish in the pelagic region who belong to the Osteichthyes (Osty-ichtheese) class of organisms.
(i) These organisms have a skeleton made of bone
(ii) There mouth is usually at the ends of their body (Terminal)
(iii) They have soft scales covered with a thin layer of tissue and mucus
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B) The biology of fish and sharks
a) There are many differences between bony fishes and sharks beside there skeleton
(I) These animals mainly differ in the their locomotion, Feeding, Respiration, Osmoregulation, and Sense
organs
C) The biology of locomotion
a) Myomers – bands of muscle along the fishes body that create the motion necessary for a fish to swim
b) Myomers help a fish swim by alternating contraction and relaxation of the myomers along the sides of the
body.
c) Though all fish swim, they have adapted specialized swimming styles according to their environment
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2) Adaptations to fins
a) All fish for fill a particular ecological
niche that requires specialized tasks
finding mates, avoiding being eaten,
hunting food
(I) These tasks have caused many
variations in fins to be developed
3) Both bony and cartilaginous fish have 4
Different sets of fins
a) Fins increase surface area to develop
more thrust against the water.
b) Every fish has 4 sets of fins:
(I) Caudal fin - provides thrust,
(II) Pectorals – help steering and breaking
(III) Pelvic fins – helps in steering and keeping balance
(IV) Dorsal/anal – helps the fish stay upright
like
and
4) The main differences in locomotion between bony and carlagionous fishes that sharks use their fins partly for
buoyancy where as boney fish use there fins to gain superior maneuverability and locomotion
a)
Chondrichthyes Locomotion:
(i) Sharks tend to sink because they
don’t have a swim batter,
(ii) Heterocercal caudal fin - large stiff
pectoral fins which provide lift
The thrasher shark has the most pronounced Heterocercal
caudal fin shape. Scientists believe it uses its tail as a whip
to stun prey before eating it.
b) Osteichthyes Locomotion:
(i) Unlike Cartilaginous fish, bony fish have adapted 4 different shapes to their caudal fin braced on
their environmental needs.
 In general a caudal fin can be specialized in acceleration and maneuvering, or prolonged
continuous swimming but not both
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 This is because those fins that are more specialized in acceleration and maneuvering create
a lot of drag which is bad for prolonged swimming
(II) Types of bony fish caudle fins:
(i) Rounder Caudal Fin and Truncate caudal fins – Best at acceleration and maneuvering but worst at
prolonged swimming
(ii) Forked Caudal Fins – not good at acceleration and maneuvering but ok at prolonged swimming.
(iii) Lunate Caudal Fins – worst at acceleration and maneuvering but best at prolonged swimming
Truncate
Rounder
Forked
Lunate
(iv) Bony fish have also flexible pectoral fins that help them have greater maneuverability
(v) Manny fish have fins that are specially adapted to where they live and hunt
 Fish that live in coral reefs and kelp beds and other tight spaces use their caudal fins almost
solely as rudders and propel themselves mostly with their pectoral fins (Wrasse, surgeon fish,
parrot fish)
 Some bottom fish rest on the bottom of the ocean using modified pectoral and pelvic fins
 Flying fish have pectoral fins modified to help them glide through the air
Manny fish have fins that are specially adapted to where they live and hunt
flying fish
walking fish
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D) Biology of feeding
1) Both cartilaginous and boney fish have mouths adapted to suit their variety of diets.
a) Cartilaginous fish tend to have mouth adapted for biting and tearing from larger prey where as boney fish
tend to have a variety of shapes and designs of mouths that are adapted to their diets
2) Feeding in Chondrichthyes:
(I) Unlike most carnivores sharks eat by taking bites out of large organisms, not swallowing smaller
organisms
(II) Most sharks mouths are adapted to have rows of teeth that help them bite and tear off peaces of larger
pray
(III) Only Whale sharks, Basking sharks, and mega mouth sharks are filter feeders
(i) Filter feeding sharks have large mouths with small teeth that is good for straining through large
quantities of water
Most sharks have teeth specialized for
bighting and tearing
The basking shark is one of only a few
Chondrichthyes animals that filter feeds
3) Feeding in Osteichthyes:
a) Most boney fish are totally or mostly carnivorous and so they have moths adapted to help them capture,
grasp, and hold their pray which is usually swallowed whole
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Barracuda have large moth with big teeth that is used to tare off chunks
of prey. Parrotfish use their beak like moth to graze on coral polyps
found in hard coral along with the algae growing on coral. Herring and
sardines have large moth that help them filter feed
E) Biology of Respiration
1) Both bony fish and cartilaginous fish breath by extracting dissolved oxygen from the water however sharks
repertory system is much more primitive and insufficient than bony fishes.
a) Reparation in Chondrichthyes
(i) Sharks need to swim in order to breath
(ii) Sharks open and closer their mouth while
swimming
which helps force water over their gill
slits
(iii) For rays and skates which spend most of
their time
resting on the bottom of the ocean, this
forward
motion is limited. These animals use a
modified
pair of gill slits called spiracles to help
move
water over their gills
b) Respiration in Osteichthyes:
(i) Boney fish have gill covers that remain
the mouth is open and water is sucked in.
mouth closes the gill covers open and
what forces water over the gills
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Marine Science - Pelagic Notes – Page 9 of 13
closed as
when the
that is
Sharks have no way for forcing water
over there gills except for swimming
(ii) Countercurrent system of
flow – boney fish also have
a modified circulatory
system which allows blood
to flow over the gills in the
opposite direction that
water flows over the gills.
 The countercurrent
system of flow allows
the most oxygen
deprived blood to meet
the most oxygen rich
water and thus a
maximum of oxygen
can be extracted from
the water
F)
Bony fish have a more advanced repertory system. They have
specialized fins over their gills that helps circulate water over their
gills without swimming
Biology of osmoregulation
1) Osmoregulation – the ability of salt water
organisms to regulate the amount of salt in
their bodies so they don’t dehydrate living
in the ocean
a) the blood of both sharks and bony fish
is less salty than seawater and thus
without osmoregulation both animals
would dehydrate and die
2) Osmoregulation in Chondrichthyes
a) To prevent dehydration sharks and
other cartilaginous fish concentrate
urea (one of the main components of
urine) in their blood which makes the
consentrations of solutes in their blood
closer to or even higher than that of
sea water
b) Excess salt is secreted via the gills, skin
and urine
3) Osmoregulation in Boney fish
a) Urea is toxic to boney fish and so they
must separate the salt from the water
using their kidneys.
b) Bony fishes kidneys retain water and
excrete only a little water through their
highly concentrated urine
Cartilaginous fish keep from dehydrating by making dissolving large
amounts of solute in there blood. Bony fish instead have specialized
kidneys that can remove the salt from their body before it causes a
problem.
G) Biology of hunting and finding prey
1) Sense organs both boney fish and cartilaginous fish have a highly developed sense of smell and taste through
special organs located on their mouth lips fins and skin that help them locate prey in the open ocean
a) Chondrichthyes
(I) Have a week sense of vision with little to no color vision
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(II) Ampullae of Lorenzini – a special sense organ located in the head of cartilaginous fish that can detect
week electrical signals given off by the nervous systems of their pray
Some shark biologists take advantage of the large
amount of Ampullae of Lorenzini in sharks noses by
massaging the nose of sharks which causes such
extreme sensation the shark is rendered paralyzed.
hammerheads eat mostly benthic organisms and so they have
adapted a flattened head which maximizes the amount of
Ampullae of Lorenzini that are present and help this
cartilaginous fish sense week electrical signals of organisms
burrowing deep in the sediment
b) Boney fish
(I) Bony fish have developed a number of adoptions to hunting food.
(i) They have a lateral line which helps in schooling and sensing when food is near
(ii) They have specialized muscles to help in seeking prey
(iii) Some fish even have a modified circulatory system which warms there blood and increases
metabolism
(II) Have a good sense of vision but can only focus by physically moving closer or further away
(III) Lateral line – a system of small canals that run along the body of the fish and allow it to sense vibrations
in the water
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c) Bony fishers adaptations
Mobility
(IV) Mobility of a fish
depends heavily on the
quantity and type of
muscle the fish has
(V) There are two types of
muscle, Red and white
b) Red mussel vs. White
muscle
(I) Red mussel contains
myoglobin, which is a
pigment that carries
oxygen.
(i) This allows red
muscles to store
oxygen in the
tissues which helps
for
more
red
more
Scientists think that fish use their lateral line to help with them stay
in formation while.
for
prolonged mussel use
(ii) Cruisers - Hunt by actively
seeking prey.
 Because cruisers need to
sustain swimming for long
periods of time in order to
hunt they Contain mostly
red muscle
 On top of that many
cursers have a modified
circulatory system that
warms the fish and allows
it to burn energy more
efficiently when in pursuit
of prey
(II) White muscle tissue fatigues much
more rapidly than red muscle
tissue. However it provides great
acceleration in short bursts.
As cold blood flows back to the fishes hart it flows past warm
(i) Lungers - Sit and wait patiently
blood coming from the hart. As a result the warm blood heats the
for food
cold blood and the fishes body temperature becomes warmer
 Because lungers only
than the surrounding water
travel short distances
through water in short bursts when they hunt they contain mostly white muscle tissue.
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Marine Science - Pelagic Notes – Page 12 of 13
White mussel tissue is characteristic of lungers
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Red mussel tissue characteristic of cruisers.
These organisms usually have modified
circulatory systems as well