Chapter 8
Marine Fishes
Phylum Chordata
Subphylum Vertebrata
Classification of Fishes
Marine Fish
• First vertebrates - 500 million years ago
• Oldest and largest group of vertebrates
• 24,000 known species of fish, 15,000 marine
• Bilateral symmetry
• Endoskeleton
Vertebrates: An Introduction
• Have a backbone (also called vertebral
column or spine)
• The backbone encloses and protects the
nerve cord or spinal cord
• The spinal cord ends in a brain
protected by a skull
Types of Marine Fish
1.
Agnatha (jawless fish)
• Hagfish
• Lampreys
2. Chondrichthyes (cartilaginous fish)
• Sharks
• Skates
• Rays
• ratfish
3. Osteichthyes (bony fish)
• Lobe-finned fishes
• Ray-finned fishes
Types of Marine Fish
Class Agnatha (Hagfish and Lampreys)
– Most primitive fishes living today
– These jawless fish have a muscular, circular mouth
with rows of teeth in rings and feed by suction
– Long, cylindrical body
– Lack paired fins and scales seen in other fish
Types of Marine Fish
A. Hagfishes or “slime eels”
– 20 species
– Exclusively marine
– They feed on dead and dying fish and
marine mammals
– Live in burrows in soft sediments
– Produce large quantities of mucous from
glands in the skin to protect them while
feeding
Hagfish
Hagfish video
• http://www.youtube.com/watch?v=NYRr_
MrjebA
Types of Marine Fish
B. Lamprey
– 30 species
– Freshwater (most) and Marine
– Adults of some species live in sea, but return to
freshwater to breed
– Adults normally die after breeding.
– Other species live in freshwater lakes
– Attach to other fish and suck their blood
Lamprey
Lamprey
• http://www.youtube.com/watch?v=xKJZ22-wTQ
Advanced Groups of Fish
• Fishes in the Chondrichthyes and
•
Osteichthyes are considered to be more
advanced.
General Characteristics (advancements) seen
in these groups:
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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
External Anatomy of More
Advanced Fish Groups
• These representative fish show the position of fins in
cartilaginous and bony fish.
Types of Marine Fish
2. Class Chondrichthyes – Cartilaginous fish
•General Characteristics of Group:
– About 1000 species
– Sharks, rays, skates and ratfishes
– Skeleton of cartilage -lighter and more flexible than bone
– Movable jaws with well-developed teeth
– Placoid scales and paired fins
– scales cause rough, sandpaper skin
– Spiracles in many species (openings on head used to bring
water directly in for respiration without opening the mouth)
– Males in most species have projections of the anal fin called
claspers that are used in copulation
Placoid scales
Paired fins
Class Chondrichthyes
Sharks
•350 species well adapted for fast swimming (fusiform shape) and
predatory feeding
•Some have not changed for 100 my
•Caudal fin (tail) well developed and powerful
–
Heterocercal – upper lobe longer than lower
•Two dorsal fins and paired pectoral fins
•5-7 gill slits behind head on either side
•Powerful jaws with several rows of teeth that move forward
Shark Diversity
Shark Diversity
Class Chondrichthyes
Shark Diversity – found in all oceans and depths
•Hammerhead – wide flattened head acts as rudder and widens sensory
organs for better reception
•Sawsharks – long, flattened head with teeth
•Thresher sharks – long upper lobe on tail to herd and stun fish
•Spined pigmy shark – 10 inches
•Whale shark – 60 feet filter feeders (plankton)
•Great white shark – 20 feet
http://www.youtube.com/watch?v=n9L4M
wn6wu0
Class Chondrichthyes
• Rays and Skates
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500 species
Dorsoventrally flattened
Demersal – bottom dwellers (some cover with sand and hide)
Pectoral fins flat and expanded – wings
5 pairs of gills slits on ventral side
Spiracles on dorsal side
Class Chondrichthyes
• Rays
– Large flattened teeth for feeding on molluscs and
arthropods
– Have long whip-like tails; in sting rays, there is a spine (barb)
at the base of the tail with an associated poison gland
– Stepping on a ray or making contact with the ray may eject
venomous spine
– Electric rays have organs that produce electricity on either
side of head
Types of Rays and Skates
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Stingrays
Bat ray
Cow nosed ray
Electric rays
Eagle ray
Bull ray (killed Steve Irwin)
skates
Cow nose ray
Bat ray
Eagle ray
Bull ray
Sting ray
Ray and Skate Video
• Stingray national geographic
• http://www.youtube.com/watch?v=Nbuu1
Fa-c1k
Class Chondrichthyes
• Skates
– Dorsoventrally flattened with pectoral fins modified into
wings
– Rays are less mobile than skates
– Skates have a fleshy tail and no spine on the tail
– Major difference:
– Rays are viviparous (bearing live young)
– Skates are oviparous (laying eggs)
– After fertilization, the female lays egg cases with an embryo
inside
– The embryo develops within the protection of the egg case
for weeks to months
– They are also demersal and feed on molluscs and arthropods
primarily
Mermaid’s Purse
Class Chondrichthyes
• Ratfishes (Chimaeras)
– 30 species
– Deep water inhabitant
– One pair of gill slits is covered by a flap of
skin
– They feed on the bottom on crustaceans
and molluscs primarily
– Heterocercal tail like in sharks
– Unlike others in this group, they also have
fin rays (tiny support rods) in the fins
Ratfishes or
chimaeras
Hydrolagus colliei
Types of Marine Fish
• Class Osteichthyes - The Bony Fish
Skeleton composed of bone
Over 23, 000 species worldwide
Gills used for respiration
Homocercal tail (two lobes of equal size) provides
forward thrust
– Cycloid (smooth) or ctenoid (spiny) scales
– Operculum – boney flap protecting gills
– Swim bladder – change depths (heavy skeleton)
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Swim Bladder
• Swim bladder used for buoyancy control (some
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bottom dwelling fish lack swim bladder)
Sound, pressure detection
Bony fish ONLY- (ex. NOT in sharks)
Biology of Fishes
• Ichthyology – study of fishes
• Body shape – related to lifestyle
– Fusiform – streamlined, strong, fast
– Compressed- thin, easy, quick short
bursts
– Depressed – flat, demersal, “fly” through
water
– Some irregular shapes can act as
camouflage among seaweed, or rocks
Coloration
Biology of Fish - Coloration
• Coloration
– Cryptic coloration – color to blend in with
environment
– Bright colored – chromatophores
– Structural colors – skin reflects only certain colors
• Shiny iridescent fishes
– Warning colors – advertise they are dangerous,
poisonous, or taste bad
– Disruptive coloration – stripes break up outline of
fish
• Difficult to pick out single fish from group
– Countershading – light ventral and dark dorsal
Cryptic Coloration
Bright Coloration
Structural Coloration
Warning Colors
Disruptive Coloration
Biology of Fish - Locomotion
• Most fish exhibit an “s-shaped” swimming pattern
– Pushes against water to move body forward
• Some move a) whole body, b) tail end, C) other fins, d)
caudal fin
• Myomeres – muscles run along sides of body
Biology of Fish - Locomotion
• Sharks use fins for lift
• Bony fish use swim bladder
• Dorsal and anal fins provide steering and
stability (no rolling)
• Pectoral and pelvic fins help turn, balance, and
brake
Biology of Fish - Feeding
• Most sharks are carnivores – bite prey larger
than themselves
• Many cartilaginous fish are filter feeders
• Bony fish are diverse in how they feed,
though most are carnivorous
– Protrusible jaws allow more flexibility in feeding
habits
Biology of Fish - Feeding
• Different mouths have evolved for different diets
– Teeth for rasping prey or biting off chunks
– Huge mouths swallow large prey or filter feed
– Beaks for biting hard coral
– Downward pointing mouth – bottom feeders
Biology of Fish - Digestion
• Digestion accomplished with stomach,
intestine (with anus or cloaca), liver, pyloric
caeca and pancreas
– Cloaca – one exit for feces, urine and gametes
• The stomach– stretch receptors in the wall of
the stomach indicate when a meal is present
Biology of Fish - Digestion
• The intestine, pyloric caeca, pancreas and
liver all secrete digestive enzymes
• The intestines of carnivorous fish=short and
•
straight
Intestines of herbivorous fish = longer and
more coiled
Biology of Fish -Circulatory
System
• Fish have a two chambered heart that serves
to pump blood throughout the body (in
contrast to the 4 chambered heart seen in
mammals)
Biology of Fish – Respiratory
System
• Irrigation of the Gills
– Extract oxygen from water; water flows
over gills
Biology of Fish – Respiratory
System
• Structure of Gills
– Gill arch – supports two gill filaments
– Gill rakers – block food from entering gills
• Filter feeders use them to gather food
– Gill filaments have lots of capillaries for gas
exchange
• Lamellae – discs that increase surface area
Biology of Fish – Respiratory
System
• Gas Exchange
– Oxygen diffuses from water into capillary
blood
• Blood flows in opposite direction of water flow called
Countercurrent System of flow or Countercurrent
Exchange
– Dismisses CO2 at same time
– O2 and CO2 carried by hemoglobin
– Muscles use lots of O2 and use myoglobin to
store O2
– http://www.youtube.com/watch?v=cVFqME-NW9s
Biology of Fish – Regulation
of Internal Environment
• Water is very solute-rich, fish have a
tendency to gain solutes and lose water
• Fish need to have mechanisms to combat this
issue – this is called osmoregulation
Fluid Balance in Fish
• Methods of Osmoregulation:
– Swallow seawater but them expel the solutes in
the digestive process (keep the water and lose the
solutes)
– Pass very little urine highly concentrated with
solutes with very little water content
Fluid Balance in Fish
• Osmoregulation cont:
– In cartilaginous fish, the blood is kept at about the
same concentration as seawater
– Keep urea in the bloodstream (this toxin is filtered
out of the blood by other organs)
– If salt enters through gills or feeding – rectal
gland expels salt
Osmoregulation
• Freshwater fish:
– Water diffuses in
– Ions diffuse out
– Drink little
– Lots of dilute urine
– Actively reabsorb ions by kidneys and gills
Osmoregulation
• Saltwater fish
– Water diffuses out
– Ions diffuse in
– Drink a lot
– Concentrated urine
– Actively excrete ions by kidneys, gills, and
gut
Biology of Fish - Nervous
System
• CNS – brain and spinal cord; nerves connect
• Fish also possess olfactory sacs (with nostrils) for
smelling
– Sharks can smell blood 1 part/million
– Salmon – recognize smells for migration
• Taste buds are located in the mouth, lips, barbels
(organs near mouth of bottom feeders) and skin
Biology of Fish - Nervous
System
• All fish rely heavily on the lateral line system
– Pores and canals lined with cells called neuromasts
that are specialized to detect vibrations
• These vibrations can indicate a predator or prey
or the position of other fish in a school
• Cartilaginous fish have ampullae of Lorenzini
– Detect electrical fields
– Help some detect hidden prey in sediment
Lateral Line
nerves
Biology of Fish - Nervous
System
• In humans, the lens changes shape for focusing on
•
•
items
In fish, the position of the lens changes like in a
camera
In some sharks, the eye is covered by a nictitating
membrane that covers the eye –protect the eye,
especially during feeding
The Fish Nervous System
• The inner ears are set in fluid-filled
canals with sensory cells similar to the
lateral line system.
Behaviors in Fish
• Territoriality
– Some territorial all the time, others only
during reproduction
– Maintain territories by “posturing”
• Raised fins, open mouth, darting, etc.
– Fights are actually rare
Territoriality
Behaviors in Fish
• Schooling
– Schooling is used by a wide variety of fish
– Fish appear much larger (as thus avoid
detection by predators)
– Harder for a predator to capture any one
fish
– Because of this, many fish school as
juveniles
– More efficient swimming?
Fish Schooling
Behaviors in Fish
• Migrations
– Mass movement from one place to another
• Once per day, year, or lifetime
– Onshore to/from outshore
– Vertical migration
– Transoceanic – tuna, salmon
Behaviors in Fish
• Migrations
– Anadromous –sea, migrate fresh for reproduction –
Pacific salmon and the Skipjack tuna
• Homing behavior – sexual maturity swim up rivers or
stream where they were born
– Catadromous – fresh, migrate marine for
reproduction – freshwater eels (Anguilla)
Reproduction and Life
History
• Cartilaginous fish use cloaca; bony fish use urogential
opening
• Sex hormones control the development of sperm and
eggs in fish
• The release of sex hormones cued by environment
• Broadcast spawning is most common
• Internal fertilization
– Typical among cartilaginous fish using claspers
Reproduction and Life
History
• Some fish are hermaphroditic
• Simultaneous hermaphrodites- produce both – can
even fertilize themselves
• Other species possess these structures at different
times during the life (sequential hermaphrodites)
Reproduction and Life
History
• Types of Sequential Hermaphrodites
– Protandry - male to female
– Protogyny –female to male
Reproduction and Life
History
• Behaviors are cues for the release of eggs
•
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and sperm (this helps ensure fertilization)
Color changes or body structure changes may
indicate readiness for reproduction
Courtship behavior – dances, displays, etc
Reproduction in Fish
• Depending on the species, fish can either be:
– Viviparous – young are born live
– Oviparous- egg layers
– Ovoviviparous – eggs are kept inside and “hatch” before
being released from female reproductive tract
– Most laying eggs in large numbers to not protect
– Some laying eggs in small numbers will protect