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Chapter 8
Marine Fish
Figure 8.01
Figure 8.02
Characteristics of Subphylum
Vertebrata
 A notochord that has developed into a spinal cord protected by
vertebrae and a head with a brain characterize organisms in
this subphylum.
 Vertebrates consist of the most complex, large, fast, and conspicuous
organisms. They include us, the organism that has had the most effect
on the global biosphere.
Significance of Class Agnatha
 This is the class of the jawless fish.
 Species include lampreys and hagfish.
 Organisms in this class are significant because they may
represent the ancestor of bony fish/sharks.
 Scientists theorize that during the Cambrian period the first
of three gill arches on a jawless fish evolved into the first jaws.
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Having jaws allowed vertebrates to become very successful predators.
Having jaws put organisms in class Chondrichthyes (sharks and rays) and class
Osteichthyes (bony fish) near the top of marine food webs.
Characteristics of Sharks and Rays
 Class Chondrichthyes includes sharks, rays and their close relatives.
 Sharks and rays don’t look similar on the outside, but
share a basic anatomy that classifies them together.
 Sharks and rays are jawed fish, that lack a swim
bladder, and have cartilaginous skeletons.
Special Attributes of Sharks and Rays
 Sharks and rays are successful predators:
 Subclass Elasmobranchii have cartilaginous skeletons.

This characteristic saves energy. Saving energy is one of the
things that have made them successful predators.
 Sharks have a sense of smell that detect incredibly
diluted substances.
 Sharks have a “conveyor belt” of multiple rows of teeth.
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They swing into place as old teeth wear out and fall away.
Special Attributes of Sharks and
Rays
(continued)
 Sharks and rays have other interesting characteristics:
 Both have lateral lines – lines of sensory hair along the
length of the body
that detect water motion and vibrations.
 Unique to elasmobranchs is electroreception – the ability to
sense minute electricity created by muscles and nerves.
 Sharks and rays have organs called ampullae of Lorenzini
which you can see as visible pits near their snouts used to
detect the electrical current.
5-6
Special Attributes of Sharks and
Rays
(continued)
 Elasmobranchs differ in their reproductive strategy.
 Sharks and rays produce fewer, but more mature offspring.
 Most fertilize their eggs internally.
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The male deposits sperm in the female via a pair of copulatory organs called claspers
found at the base of the pelvic fins.
The female lays an egg case in which the juveniles develop for up to six months at
which time one or more sharks or rays emerge.
 A few shark species are ovoviviparous – the eggs hatch within the mother’s
body.

They give birth to live young rather than egg cases.
 The largest fish in the ocean.
 Shark size ranges from hand-sized to the
whale shark – the largest fish in the ocean.
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Whale sharks can reach 14 meters (46 feet).
Basking sharks can reach 10 meters (33 feet).
Megamouth sharks can reach 6 meters (20 feet).
 All three are filter feeders that consume plankton.
Special Attributes of Rays
 Superorder Batidoidimorpha of subclass Elasmobranchii consists of the
rays, which includes skates and guitarfish.
 Ray anatomy is well suited to life on sandy
bottoms or midwater.
 Specially adapted to life in midwater are
the eagle ray and manta ray.
 Pectoral fins have become “wings” that
stretch forward over the gills and are fused
to the sides of the head.
 Shoulder girdles are flattened and many
bones are fused together for rigidity.
 No longer need a tail for swimming, the tail
has become a defensive whip in some species.
 Rays literally fly through the water.
 The largest rays are mantas with wingspans
exceeding 8 meters (26 feet).
 Like the largest shark, the mantas feed on plankton.
Figure 8.14a
Figure 8.12a
Figure 8.26
Figure 8.04
Figure 8.05b
Figure 8.06b
Figure 8.07
Figure 8.08a
Characteristics of Bony Fish
 Class Osteichthyes are jawed fish with bone skeletons.
 Most have a swim bladder and scales.
 Most control buoyancy by adding or releasing gas to/from their
swim bladder.
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They control the swim bladders with oxygen gas exchanged to and from
blood circulation.
Many have a special organ called the gas gland and the rete mirabile
that take up gases from the bloodstream for the swim bladder.
This allows many species to hover nearly motionless in midwater.
 Most bony fish reproduce externally.
 The female lays her eggs, the male
immediately fertilizes them.

5 - 17
Their strategy is to produce a vast number
of off-spring with only a few expected
to survive to maturity.
Characteristics of Bony Fish
(continued)
 Bony fish have characteristics for life on the reef and for life in the
open ocean:
Bony Fish – Half the World’s Vertebrates
 Bony fish have lateral lines that detect water
motion and vibrations.
 Most open ocean and schooling fish have a torpedo-like
streamlined shape that minimizes drag and turbulence.

This fusiform shape is spindle-like, slightly broader at the
head and a V-shaped tail. This makes them fast swimmers.
 Most open-ocean and schooling fish have a lighter underside and dark
Chapter 5 Pages 5-74 & 5-75
topside for concealment.
 Bony fish living in reefs and on the bottom use
survival strategies more diverse and include
concealment and armor instead of swimming.
5 - 18
 For this reason, you see far more diversity in color,
shape, and size among reef and bottom fish.
Types of Marine Fish
 Agnatha
 These jawless fish have a muscular, circular mouth with
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rows of teeth in rings
Long, cylindrical body
Lack paired fins and scales seen in other fish
Two types of jawless fish exist- hagfish and lampreys
Ectothermic
Lamprey – www.wikipedia.com
Types of Marine Fish
 Hagfishes
– 20 species
– Exclusively marine
– They feed on dead and dying fish and marine mammals
primarily
– Live in burrows in soft sediments
– Produce large quantities of mucous from glands in the
skin to protect them while feeding
www.wikipedia.com
Pacific Hagfish (Eptatretus stoutii)
- 4 pairs of sensory tentacles around mouth
- 12 pairs of gill slits
- SLIME
Types of Marine Fish
 Lamprey
 30 species
 Live in freshwater (lakes) and salt water
 Adults of some species spend a large portion of their life
in the sea, but return to freshwater to breed; adults
normally die after breeding.
 Parasitic: They feed on living fish by rasping into the
sides of fish with their sucker-like mouth and
consuming blood, tissue and body fluids

Produce anticlotting agent
More
Advanced
Groups
of
Fish
 Fishes in the Classes Chondrichthyes and
Osteichthyes are considered to be more advanced.
 General Characteristics (advancements) seen in
these groups:
– Highly efficient gills
– Scales cover the body
– Paired fins
– A wide variety of jaw and feeding types
– Lateral line and other sensory organs
– Streamlined body
Osteichthyes, The Bony Fish
 Skeleton composed of bone
 More species that all other vertebrates combined- over
23,000 species worldwide
 Gills used for respiration
 Hinged jaws allow for a variety of different feeding
strategies
 Homocercal tail (two lobes of equal size) provides forward
thrust
www.wikipedia.com
Osteichthyes, The Bony Fish
 Flat bony scales protect body
 ctenoid (tiny spines) or cycloid (smooth)
 Bony operculum covers the gills (provides better
protection against injury compared to gill slits for each
gill)
 Lateral line used in sensory capacity and
communication
 Swim bladder used for buoyancy control (some bottom
dwelling fish lack swim bladder)
 Variable body plans are adapted for specific
environments
Osteichthyes, Body Shape
 Body shapes vary greatly
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dependent on the niche
Ex. flounders and soles (flat shape)
live on the bottom and cover
themselves slightly with sand to
camouflage themselves from
potential predators as well as prey
Osteichthyes – Body Shape of
FAST fish
 Tuna, billfish, and other fast moving predators are long,
streamlined and most of their fins serve as rudders (very
little flexibility except in caudal fin)
 This body shape allows these predators to cut through
the water quickly
 Notice, too, that the area of the body called the caudal
peduncle (area just before the tail) is very thin – this
allows all the muscles to concentrate in this area
allowing for greater thrust of the caudal (tail) fin (this
means FAST swimming capabilities)
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Sailfish
Osteichthyes – Body Shape of
not so fast fish
 Angelfish – coral reef fish example – not open ocean fish
 Angelfish and the like inhabit coral reefs, oyster reefs
and other similar environments
 In these fish, the body is not as streamlined and the fins
are feather-like for lots of flexibility
 This flexibility allows for greater control around the
features that would be seen in a coral reef type
environment (crevices, etc)
–
Humphead parrotfish
www.animalphoto.tk
Osteichthyes – Shape of fish
that don’t swim far
 Other fish have a shape that allows for camouflage in
their environment
 For example, fish like the toadfish and the stonefish
actually look like rocks or “scenery” and thus can go
undetected by predators or prey
www.fishimage.blogspot.com
www.njsciba.net
Osteichthyes
–
Color
Patterns
Countershading is seen in virtually all fish species
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In countershading, the ventral (belly) area of the fish is lighter
than the dorsal area of the fish
This allows the fish to “blend in” with the environment
If a fish is seen from above, the darker coloration of the dorsal
area blends in with the darker color of the ocean bottom
If the fish is seen from below, the lighter coloration of the
ventral surface blends in with the lighter coloration of the
ocean surface
www.nationalgeographic.com
Osteichthyes,
The
Bony
Fish
– Coloration patterns:
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Slower swimming fish often have bars or stripes that help
break up the silhouette of a fish (a form of disruptive
coloration)
This helps with predator avoidance
Some also have coloration that helps them blend in with
environment (known as cryptic coloration)
www.sunysb.edu
Osteichthyes,
The
Bony
Fish
Coloration Patterns:
 Circular patterns on or near the caudal fin
 Confuses predators who are not sure which end of the fish is the
head
 If fish attacked on caudal end where the black dot looks like an
eye, she can probably get away with minor damage
 If attacked on his head region, she may sustain serious, life
threatening damage
 Warning Coloration –
 use color to advertise their bad taste or poisonous nature –
www.animalworld.com
www.fishwallpaper.net
www.inkart.net
Swimming Patterns
 Fish exhibit an “s-shaped” swimming pattern
 Bands of muscle along the body called myomeres drive
this swimming motion
 Depending on the type of fish, different fins may be
used primarily for the forward movement
Swimming Patterns
 A) eels swim by undulating body in lateral waves from head
to tail
 B) fast fishes with shorter bodies – flex caudal tail
 C) surgeonfishes, parrotfishes – move only the fins
 D) trunkfishes and porcupine fishes swim slowly by
moving base of tail and rest of body remains immobile
Specializations for swimming
 Myomeres – bands of muscles that produce rhythmic
contractions for swimming in S-pattern
 Swim bladders in bony fish
Swimming
Patterns
 In bony fish, pectoral fins are not needed for lift (like in
sharks) and thus are normally not stiff in construction
(exception: fast swimming species like tuna, billfish, etc)
 In contrast, the pectoral fins in many bony fins are flexible
and used for maneuverability
 In some slower-swimming species, forward movement is
mainly provided primarily by the pectoral fins (see fish in
tanks! – coral reef fish)
 In other species, all the fins may be flexible and highly
modified for camouflage (example: sea horses and leafy sea
dragons and weedy sea dragons
 Fins will not allow for significant forward movement
 Flying fish example
Fish Gills
 The construction of the gill is the same in all fish –
Gill arch supports the entire structure
 Gill rakers are on the forward surface of the gill arch and
 Gill filaments trail behind the gill arch
 Like in the human lung, exchange of oxygen and
carbon dioxide takes place on these surfaces
Figure 8.17 The gills of fishes
are very efficient for gas
exchange. Bony fishes have 4
pairs of gills (a), each containing
2 rows of gill filaments (b).
Lamellae in gill filaments (c)
increase the surface area of the
gill filaments. (d) Diffusion of
oxygen from seawater into the
blood gets a boost b/c the water
flows across the lamallae in the
opposite direction to that of the
blood. (e) The concentration of
oxygen (indicated by dots) is
always higher in the water than
in the blood. If circulation were
not reversed, blood to the body
would have less oxygen.
VIDEO
Acquiring
and
Processing
Food
 Mouth structure also reveals the dietary preferences
of fish
 As an example, the “beak” (fused teeth) seen in
parrotfish allows for these fish to scrape algae and
other organisms off of hard surfaces
 The butterfly fish uses its long tube-like mouth to
feed on corals
 While the barracuda uses rows of sharp teeth and a
wide mouth to capture its prey – other fish
Acquiring and Processing Food
Jaw/Mouth Structure
Acquiring and Processing Food:
Mouth Structure
 The position of the mouth is also important
 A strongly forward facing mouth is important in fish
who chase down their prey (as seen in barracuda)
 A downward facing mouth would be seen in fish
feeding at/near the bottom (opposite for feeding on
surface of water)
Acquiring and Processing Food:
Digestion
 Organs involved: stomach, intestine (with anus), liver,
pyloric caeca and pancreas
 The stomach is structured very similarly to the human
stomach – stretch receptors in the wall of the stomach
indicate when a meal is present and needs to be
mechanically digested by the churning motion of the
stomach wall
Acquiring and Processing Food:
Digestion
 Intestine, pyloric caeca (tubes at end of intestine),
pancreas and liver (bile breaks down fat) all secrete
digestive enzymes
 The intestines of carnivorous fish tend to be short and
straight while the intestines of herbivorous fish are
longer and more coiled (plant and algae material is
more difficult to process, so it needs to stay in the
intestines longer)
Acquiring and Processing Food:
Digestion
The Circulatory System
 Two chambered heart that pumps blood
throughout the body (in contrast to the 4
chambered heart seen in mammals)
 System of arteries, veins and capillaries takes
blood to the body tissues and returns it for re-
oxygenation by the gill filaments
 O2 and CO2 diffuses across thin membranes of
capillaries either in the gills or at the tissues of the
body
Figure 8.15. The circulatory system of fishes consists of veins that
carry deoxygenated blood (in blue) from the body, a twochambered heart that pumps blood into the gills for oxygenation,
and arteries that carry oxygenated blood (in red) to rest of body).
Fluid Balance in Fish
 Remember osmosis and diffusion are always at
work in an organism
 Fish need mechanisms to combat the issue of
water loss – OSMOREGULATION
 Fish osmoregulate by:
 Swallowing seawater and expel the solutes in the
digestive process (this allows them to keep the water and
lose the solutes)
 Most marine fish pass very little urine that is processed
by the kidneys, and is highly concentrated with solutes
with very little water content
Fig. 8.18 Marine
fishes - salts excreted
by kidneys and drink
water
The
Fish
Nervous
System
 The fish have a brain, spinal cord and numerous nerves like
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other vertebrates
Smell: Fish possess olfactory sacs (with nostrils/nares)
Hearing: Inner ears are set in fluid-filled canals with
sensory cells similar to the lateral line system.
Taste: Detect chemical stimuli by using taste buds are
located in the mouth, lips, barbels and skin
Sight: The position of the lens changes like in a camera
 (Note: Different from land animals where the lens changes shape
for focusing on items
The
Fish
Nervous
System
 All fish rely heavily on the lateral line system
 The lateral line is a series of pores and canals lined
with specialized organs called neuromasts that are
specialized to detect vibrations
 Lined with hair cells – similar to those in your cochlea
 Orientation, predatory behavior, social schooling
Fish Behavior
 Schooling
 Widely used (+4000 species school)
 Why school?
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Predator deterrent
Spawning aggrigation
Migration
Enhanced foraging
Fish Behaviors
 Territoriality
 Some fish are territorial by nature all the time, others
are only territorial during reproduction
 Fish maintain their territories normally by “posturing”
to show their aggression
 Posturing can include raised fins, open mouth, darting,
etc.
 Fights between individuals are actually rare
 Damselfish and algae
Reproduction in Fish
 Sex hormones control the development of sperm
and eggs in fish
 Release of sex hormones cued by water
temperature, day length, specific tide cycles, etc.
 Broadcast spawning most common
 Some fish have internal fertilization (sperm is
inserted directly into the female by the male)
 Complex mating behaviors are seen in some
species (Ex. Banggai cardinals, potato cod)
 Color or body changes can cue reproduction
Atlantic cod mating behaviors. 1. Male establishes
territory. 2. Male makes displays (grunting, spreading fins,
etc). 3. Female (if the male is lucky) spawns with male.
Fish Reproduction
 Some fish are hermaphroditic
 Simultaneous hermaphrodites – rare (ex. salmon, some
deep sea fish)
 Sequential hermaphrodites)
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Protandry - males then females (ex. anemone fish)
Protogyny – females males (ex. wrasses, parrotfish)
 Cues for changes - changes in social structure or
environment
Fish Reproduction
 Depending on the species, fish can either be:
 Viviparous – young are born live
 Oviparous - egg layers (most common)

Some parents protect eggs, though most do not
 Ovoviviparous – eggs are kept inside and “hatch” before being
released from female reproductive tract
 RARE: Parthenogenic species - in this reproductive plan, young
develop directly from the unfertilized eggs of the female (no DNA
from males) – the young are “clones” of the female
Figure 8.08b
Figure 8.12b
Figure 8.14b
Figure 8.15
Figure 8.16a
Figure 8.16b
Figure 8.17a
Figure 8.17b
Figure 8.17c
Figure 8.17d
Figure 8.17e
Figure 8.18a
Figure 8.18b
Figure 8.19
Figure 8.21a
Figure 8.21b
Figure 8.21c
Figure 8.21d
Figure 8.22
Pg. 164
Figure 8.24
Figure 8.25
Figure 8.28
Figure 8.13a
Figure 8.09a
Figure 8.09b
Figure 8.09c
Figure 8.09d
Figure 8.09e
Figure 8.09f
Figure 8.09g
Figure 8.09h
Figure 8.09i
Figure 8.11a
Figure 8.11b
Figure 8.11c
Figure 8.11d
Figure 8.13b
Figure 8.13c
Figure 8.13d
Figure 8.13e