Marine Fishes
What is a fish?
Classic definition:
• Any of numerous cold-blooded aquatic vertebrates of
the superclass Pisces, characteristically having fins,
gills, and a streamlined body, including specifically
– Any of the class Osteichthyes, having a bony
skeleton, and
– Any of the class Chondrichthyes, having a
cartilaginous skeleton and including the sharks,
rays, and skates.
Although this is all accurate...we will find that fish are
considerably MORE!!
Fish similarities...
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Vertebrate ( chordate)
Gills
Poikilothermic
Fins
Scales
Drag Reduction Features in Fish
• “Fusiform” body shape
– Reduction of body wave amplitude
– Reduction of surface area
– Boundary layer modifications
What is a fusiform body shape?
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pointed leading edge
maximum depth 1/3 body length back from head
posterior taper
caudal fin interrupts ideal fusiform shape
– Class Pteraspidomorphi (sp. diplorhina = “two nares”)
– they literally had two separate olfactory bulbs in the brain.
– those with a different shell, i.e. dermal armor
Ostracoderms
Hagfish (Agnatha): jawless fish
Lamprey
• Predatory/parasitic
• Rasping teeth
Parasitism of Great Lakes fishes…
Placoderms - earliest gnathostomes
(jawed vertebrates)
• True jaws = more food!
• Paired fins = more food!
Cartilagenous Fishes
(Sharks, Skates and Rays)
Distinguishing Elasmobranch Traits
cartilaginous skeleton
no swim bladder
heterocercal tail
placoid denticles - scales and teeth
spiracles present with 5-7 gill slits (no operculum)
urea retained for osmoregulation
spiral valve in intestine
Elasmobranch…
males have claspers, internal fertilization plate or strap gill
oviparous, ovoviviparous, viviparous
teeth in rows, are constantly replaced
Sharks exhibit extreme variability in size, shape and abilities.
Nearly 850 spp. of sharks, 350 exhibit typical
body morphology.
Carchariniformes – basking sharks, filter feeder
Cetorhinus maximus
Mako
Isurus oxyrinchus
Great White
Lamniformes - mackerel,
mako, white sharks
-carnivores
Great White, Carcharodon carcharias
Skates and rays spend most of their lives near (on) the
ocean floor eating molluscs, squid, and small fish.
Yellow stingray, Urolophus jamaicensis
Like sharks, skates and rays come in
many shapes and sizes.
Blue spotted ray, Taeniura
lymma
Skates (order Rajiformes)
•pelvic fin divided into two lobes
•tail relatively stocky, no spine
Rays (order Myliobatiformes)
•each pelvic fin with one lobe
•tail relatively slender to whip-like spine
Spotted ratfish Hydrolagus colliei
Family: chimaeridae
• Identification: Broad, flat, duckbill shaped snout
containing incisor shaped teeth. Prominent, venomous
spine at leading edge of dorsal fin. Tapering tail
constitutes almost half overall length.
Coloration brown or grey with white spots. Skin
smooth and scale less. Can give off an iridescent,
silvery sheen. Fins grey or dark.
• Size: up to 97cm in length.
Boneless
vs.
Bony
Placoid scales
Found in sharks and rays, and can
vary greatly in external
appearance. They do not increase
in size as the fish grows, instead
new scales are added. Placoid
scales are often referred to as
denticles.
Placoid scales consist of a
flattened rectangular base plate
which is embedded in the fish, and
variously developed structures,
such as spines, which project
posteriorly on the surface. The
spines give many species a rough
texture.
Placoid scales of the Broadnose Sevengill Shark.
Cycloid and Ctenoid Scales
Found in bony fishes (the Teleostei).
Overlapping = flexibility, over cosmoid
or ganoid scales.
Cycloid scales—smooth posterior margin,
no ctenii. (Greek "cyclo“ or circle.)
Fish form and function
show a high degree
of variation.
Coloration is also very
important in fish.
Here a stonefish “disappears”
amid the coral background.
Chromatophores, specialized
pigment cells within its
skin provide protective
coloration.
• Disrupt the outline of the fish
Good
Better
Best
• Being dark on top, light on bottom
– Look like substrate from above
– Look like water surface from below
Warning coloration! May indicate poisonous animal.
Fish Locomotion
• Primary forces involved in fish swimming:
– Thrust - force that propels forward
– Drag - friction produced from passing an object
through a medium
– Gravity – force from earth’s magnetic pull
(partially counterbalanced by density of water)
– Lift - upward force that counteracts gravity
Skeletal Fish Muscle:
•Essentially three types of fish muscle: red, white,
pink.
•Red muscle (oxidative): Highly vascularized,
myoglobin containing tissue used during sustained
swimming. Small diameter and high blood volume =
rich O2 supply! Presence leads to strong flavor in
some fishes (tuna).
•White muscle (glycolytic): Little vascularization.
Used during “sprint” swimming. Large diameter
fibers.
•Pink muscle: This one is sort of in between red and
white. Serves in sustained swimming, but not to the
extent that red muscle is used.
Swimming Styles: Body waves
Anguilliform (eel-like)
Lateral curvature in spine and
musculature that moves in a
posterior direction
Start: lateral displacement
of head, and then passage of
this displacement along the
body axis to the tail
Result: backwardfacing “wall” of body
pushing against the
water
Partial body waves
(Sub) Carangiform, Thunniform (tuna-like)
• Body wave begins posterior to head and increases with amplitude
as it moves posteriorly
• Reduced drag compared to full body wave swimming
• Wave STARTS at the caudal pedicle (deeply forked, lunate)
Caudal peduncle/fin beats Ostraciform (boxfish-like and puffer-like)
Sculling action of caudal fin—like rowing
No body waves - body remains rigid - useful for oddshaped fishes
Medial fin waves
Amiiform - bowfin-like
• Body rigid, but medial fins generate posterior waves
(forward) or anterior (reverse)
• Good for stalking or moving without disrupting body
musculature that serves as electric organ (knifefish)
• Also used for sculling - triggerfish & others
Pectoral fin beats
Labriform, wrasse-like
Similar to rowing
laterally-positioned
pectoral fins- often includes
feathering as well
Especially useful for fine
maneuvering
e.g. by deep-bodied fishes
Fish Feeding - function
• Herbivores
– < 5% of all bony
fishes, no
cartilaginous fishes
• browsers - selective eat only (that) plant(s)
• grazers - less selective include sediments
• Detriti`vores
– 5 - 10% of all species
– feed on decomposing
organic matter
Fish Feeding - function, cont.
Carnivores
– Zooplanktivores (filter feeders)
• suction feeding
• ram feeding
– benthic invertebrate feeders
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graspers
pickers
sorters
crushers
Fish Feeding - function, cont.
• Carnivores, cont.
– fish feeders
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active pursuit
stalking
ambushing
luring
Fish feeding behavior
• Fish feeding behavior integrates morphology
with perception to obtain food:
– >Search
– --> Detection
– --> Pursuit
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--> Capture
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--> Ingestion
Feeding behavior
• Fish show versatility in
prey choice and ingestion
• Behavior tightly linked to
morphology
(co-evolution)
Similar to Darwin’s finches, different shaped
mouths permit specialization on many prey
items.
Digestive
Systems
Cartilagenous
vs.
Teleost (bony)
Fish circulation is a closed system. Heart
pumps blood through a loop of arteries, veins,
and capillaries.
Gills: the best way
to gain oxygen (O2)
from an environment
where its concentration
is already very low.
Counter-current
circulation permits O2
to diffuse from high to
low concentration, even
across venous tissue
after most O2 has been
removed from the water
by gills.
Salt Balance
Revisited
Rem:
Freshwater fish
[salt] inside fish >
[salt] outside
Saltwater fish
[salt] inside <
[salt] outside fish
Structure of Lateralis
Canals
• Epidermal tunnel
• Pores open from canal to
skin surface
• Neuromasts distributed
within tunnel
• Fluid in tunnel is more
viscous than water;
therefore, more resistant
to flow
Damselfish, Chromis spp.
Lateral line also aids in navigation in close quarters.
Fish Migrations: food, spawning
Migration for some salmon is a one-way trip!
Freshwater eels, Anguilla rostrata are at the
extreme end of migratory patterns, taking an
entire life to make the round trip. Adults spend 15
years in fresh water before making the return trip
to spawning grounds.
Reproduction in Fishes
Reproductive traits and life-history patterns
Mating systems:
– Promiscuous - both sexes with multiple partners most (common)
– Polygynous - males with multiple mates (cichlids)
– Polyandry - females with multiple mates – few
(Anglerfish, males “parasitize” females,
clownfish)
– Monogamy - mating pair remains together over
time, long gestation of young (some cichlids,
seahorses, pipefish, clowfishes)
Courtship/ritualistic displays are patterns of
behavior observed in many fish.
Some marine fish have specialized reproductive
organs.
Claspers in elasmobranchs: male reproductive organ
Egg laying (ovipary) in sharks, is a common menthod
of fish reproduction.
swell shark egg, Cephaloscyllium ventriosum