Marine Fishes
• Pelagic organisms that can actively swim
(against a current) are known as nekton
• Nekton include some
invertebrates such as
cephalopods and pelagic
arthropods such as shrimp
and swimming crabs, but
most nekton are vertebrates
Phylum Chordata, Subphylum Vertebrata
• Vertebrates (subphylum Vertebrata) share
four fundamental characteristics of the
phylum Chordata with 2 invertebrate subphyla
– Subphylum Urochordata
– Subphylum Cephalochordata
• Vertebrates differ, however, in
the presence of a backbone, or
spine, and the presence of an
endoskeleton
Subphylum Vertebrata
• The vertebral backbone consists of a dorsal
row of hollow skeletal elements, the vertebrae
• The vertebrae surround and protect the nerve
cord, or spinal cord, which ends in a brain
protected by a skull made of cartilage or bone
• Vertebrates exhibit bilateral symmetry and
have a distinct head, and organ systems
Subphylum Vertebrata
Marine Fishes
• Fishes were the first vertebrates, appearing
more than 500 million years ago
Jawless
fishes
Cartilaginous
fishes
Bony fishes
Marine Fishes
• Fishes are the oldest and structurally-simplest
of all living invertebrates
• ~Half of all vertebrates are fish!
• Most species of fish are marine
• Three groups are fish are currently recognized
– Jawless Fishes (superclass Agnatha)
– Cartilaginous Fishes (class Chondrichthyes)
– Bony Fishes (superclass Osteichthyes)
General Fish Morphology
http://www.users.totalise.co.uk/~darrenbarton/id119.htm
Jawless Fishes (Agnatha)
• The most primitive of all living fish are the
jawless fish (Agnatha)
• As they lack jaws, jawless fish must feed by
suction with the aid of a round, muscular
mouth and rows of teeth
• Body is cylindrical and elongated like that of
an eel or snake; no paired fins or scales
– lack true vertebral column!
– Cartilaginous skeleton
Jawless Fish (Agnatha)
• Jawless fish include the hagfish and the
lampreys
– Hagfish feed mostly on dead or dying fishes;
usually found on deep, muddy bottoms
• Exclusively marine
– Lampreys attach themselves to other living fishes
and suck their blood and tissue matter
• Primarily freshwater
Hagfish (left) vs. Lamprey (right)
http://chrisortlepp.com/photos/Hagfish-coiled.jpg
Cartilaginous Fishes
• Cartilaginous fishes (Chondrichthyes) have a
skeleton made not of bone, but of cartilage,
which is lighter and more flexible than bone
• Cartilaginous fishes have well-developed jaws
and paired fins for efficient swimming
• Most cartilaginous fish also have rough,
sandpaper-like skin, the result of placoid
scales
pointed tip directed backwards
Cartilaginous Fishes
• Cartilaginous fishes include sharks, skates,
rays and chimeras, or ratfishes
• Nearly all are marine
• ~350 species of sharks; ~500 species of skates
and rays; 30 species of chimeras
Sharks (cue scary, cello music)
• Sharks are often referred to as living fossils
because many of the species alive today are
similar to ones that swam the seas >100
million years ago
• Sharks have powerful jaws with rows of
numerous sharp, often triangular teeth
– Lost or broken teeth are quickly replaced by
another, which shifts forward from the row behind
it as if on a conveyor belt
http://www.evolutionnyc.com//ImgUpload/P_455917_964647.jpg
Sharks
• Sharks have fusiform, spindle-shaped bodies,
which cut easily through the water
• A well-developed, muscular caudal fin propels
them through the water; paired pectoral fins
enable steering and dorsal fins provide stability
Sharks are efficient predators
• Many sharks exhibit counter-shading,
appearing dark on top and light on the bottom
– Camouflage from above and below
• Why?
flmnh.ufl.edu
Sharks, dog bites, lightning strikes, and
falling coconuts, oh my!
• Sharks have five to seven gill slits which are
located behind the head for respiration (we’ll
come back to this…)
• More than 80% of all sharks are under 2
meters in length (less than 6.6 feet), and only
a few of the remaining 20% are aggressive
towards humans
• FACT: You are more likely to die from a dog
bite (or lightening strike) than a shark bite…
Fish are friends, not food…
• In fact, sharks have WAY more to fear from
humans than we do of sharks
• Shark populations are in considerable decline
worldwide
– 80% global decline in shark populations!
– 26-73 million sharks killed every year for their fins!
– Potential increases in diseased,
unfit, and unhealthy prey
individuals
all-creatures.org
Dramatic decline in shark populations
Myers, et al. 2007
Is your dinner endangered?
Rays and Skates
• Rays and skates have dorsoventrally flattened
bodies, with 5 pairs of gill slits on the
underside (ventral side) of their body
• Most are demersal, spending much of their
lives on the sea floor
• Pectoral fins are
greatly extended
resembling wings
Is it a ray, or a skate?
• Skates usually have 2 dorsal fins; Rays lack
dorsal fins altogether
• Skates have a muscular tail; Rays have a whiplike tail, usually with a prominent stinger
Chimeras, or ratfishes
• Approximately 30 species of deep-water,
strange-looking cartilaginous fish are grouped
separately as chimeras, or “ratfishes”
• Only one pair of gill slits, covered by a flap of
skin
• Demersal (bottom-dwelling)
• Some with a long,
rat-like tail
To summarize….
Bony Fishes (Osteichthyes)
• Bony fish (Osteichthyes) are the most
successful and abundant of the 2 groups of
fishes (96% of all fish; ~27,000 species)
• Osteichthyes possess a hard, strong - but
lightweight - skeleton made of calcium that
supports them and is responsible for their
success (and diversity) as a group
• Bony fish include tuna, cod, flounder, goldfish,
and other familiar species
Bony Fishes (Osteichthyes)
• The composition of their skeleton is not the
only distinguishing feature of bony fishes
• In contrast to the tiny, pointed placoid scales
of cartilaginous fishes, bony fish usually have
cycloid or ctenoid scales, which are thin,
flexible, and overlapping
– Cycloid scales have a smooth outer edge
– Ctenoid scales have a toothed outer edge
Bony Fishes (Osteichthyes)
• The scales are made of bone and are covered
by a thin layer of skin and a protective mucus
• Bony fish are also characterized by the
presence of a gill flap, or operculum
Bony fish have a bony opeculum
Cartilaginous fish have gill slits
kmle.co.kr
Bony Fishes (Osteichthyes)
• Bony fish are subdivided into two major
groups
– Lobe-finned fishes
– Ray-finned fishes
• Lobe-finned fishes are largely extinct, but
include lungfishes and coelacanths
• Ray-finned fishes, in contrast, are far more
successful, and can be further divided into
soft-rayed and spiny-rayed bony fish
Soft-rayed vs. Spiny-rayed
• Soft rayed fish representatives include:
– Cod
– Trout
– Herring
• Spiny-rayed fish representatives include:
– Bass
– Groupers
– Reef fish
Fishes of Long Island
Striped bass
Cunner
Tautog
Porgy
Fishes of Long Island
Bluefish
Black sea bass
Weakfish
Monkfish
Flatfish (“doormats”) of Long Island
Winter flounder
KEY:
Right-sided
Left-sided
Windowpane
Summer flounder
Ontogeny recapitulates phylogeny?!!?