



Osteichthyans
Chondrichthyes
Has cycloid scales.
Has placoid scales
Presence of dermal
bone
Operculum covers the
gills
No Bones in their body
Gill Slits are exposed
(Naked)
 The
Chondrichthyes
o cartilage, composed of chondrocytes suspended
in a protein matrix.
Osteichthyes
o composed of cartilage and bone.


Scales serve as protection for the fish.
Reduces drag during swimming.
 Chondricthyes
o large scales called placoid scales
• Scales have a bone like base embedded in the skin
and a backward projecting enamel covered dentine
spine.
 Osteichtyes
o Have cycloid or ctenoid scales.
• Cycloid scales are smooth, flat and round
• Ctenoid scales posses a comb-like extensions (ctenii)
 Scales
– thin bony
plates that overlap
each other and provide
protection.
 Glands
on the scales
produce a slimy
mucus, which protects
them from bacteria.
 There
are four types of
scales:
 1. Placoid – type of
scales on sharks
 2. Ganoid – scales are
connected to each
other (like armor). Ex.
Is a Gar
 3.
Cycloid – have smooth
surfaces and edges.
 4. Ctenoid – are like cycloid
scales, but have sharp/rough
edges that stick out.

Maneuverability (steering) and propulsion

The main purpose of the dorsal fin is to stabilize the
animal against rolling and to assist in sudden turns.
o Stabilize the fish while swimming.


The paired pectoral fins are located on each side, usually
just behind the operculum, and are homologous to the
forelimbs of tetrapods.
It assists in maintaining depth as the fish swims.

The paired pelvic or ventral fins are located ventrally
below the pectoral fins. They are homologous to the
hindlimbs of tetrapods. The pelvic fin assists the fish in
going up or down through the water, turning sharply, and
stopping quickly.

The lateral line is a sense organ used to detect
movement and vibration (mechanoreceptors) in the
surrounding water. In most species, it consists of a line of
receptors running along each side of the fish.


The nostrils of fish do not open into the back of the mouth
as do those of mammals, and are not, therefore, for
breathing.
They lead into organs of smell which are as a rule, very
sensitive, so that a fish can detect the presence of food in
the water at considerable distances.


Fish see through their eyes and can detect color.
The eyes are rounder in fish than mammals because of the
refractive index of water and focus is achieved by moving
the lens in and out, not distorting it as in mammals.
GILLS
Gills
• Gills are the main
site of gas
exchange
in almost all fishes.
The gills consist of
bony or stiffened
arches (cartilage)
that anchor pairs of
gill filaments.
Microscopic gill
structure: showing gill
filament and lamellae
(Red blood cells
evident.)

Most terrestrial vertebrates have internal lungs that must
be ventilated through bidirectional movement of air to
replenish the oxygen (O2) supply

Most fish have external gills that are ventilated by a
unidirectional flow of water, by pumping or swimming

Fine sieve structure of gills very efficiently extracts O2 from
water.


Efficient O2 uptake is vital to fish because of its low water
solubility.
Oxygen is ROUGHLY 20x more abundant in the air than in the
water.

Solubility decreases with increased temperature & salinity!
Temp (C)
0
O2 con. at sat. O2 con. at sat.
(mg/l) – Fresh (mg/l) – Salt
10.3
8.0
10
8.0
6.3
20
6.5
5.3
30
5.6
4.6

Also, metabolic rate (demand for O2 ) increases as
temperature rises. (How does this affect nutrition?)

Also, metabolic rate (demand for O2 ) increases as
temperature rises. (How does this affect nutrition?)

What does this mean to fish??
In warm water...fish need to extract MORE O2 from LESS!
 Short
diffusion distance at
gill site
 Large
surface area for
diffusion at gill site
 Counter
current exchange
of gases at gill site
 Large
volume of water
passes over gills
 Fish
employ the
countercurrent system
to extract O2 from the
water.
 This
system moves
water flowing across
the gills, in an opposite
direction to the blood
flow creating the
maximum efficiency of
gas exchange.
Ram
 Uses same parts, but not the pumping energy required.
Sharks primarily. Once swimming speed is achieved...no
need to actively vent buccal cavity. However, this can
only be used consistently by strong swimmers (sharks,
tuna).
Branchial
1. Fill mouth cavity (open
mouth, expand volume of
mouth, expand volume of
gill chamber with
operculum closed)
2. Fill gill cavity (close
mouth, squeeze mouth
cavity, expand gill cavity,
with operculum closed)
Branchial
3. Expel water from gill
cavity (squeeze mouth and
gill cavities, open operculum)
4. Reset for next cycle
Branchial
Mouth
Pharynx
Operculum
Branchial Arches (gill arches)
 Physiological
systems of fishes operate in an
internal fluid environment that may not match
their external fluid environment
 Relative concentrations of water and solutes
internally must be maintained within fairly narrow
limits
 Internal environment influenced by external
environment

Osmoregulation
o

Regulates solute concentrations and balances the gain and
loss of water
Excretion
o
Gets rid of nitrogenous metabolites and other waste products

Freshwater fishes in different environments show
adaptations that regulate uptake and conservation of both
water and solutes
 Osmoregulation
is based largely on controlled
movement of solutes between internal fluids and
the external environment
 Cells
require a balance between uptake and loss
of water
 Osmolarity, the solute concentration of a
solution, determines the movement of water
across a selectively permeable membrane
 If two solutions are isoosmotic, the movement of
water is equal in both directions
 If two solutions differ in osmolarity, the net flow
of water is from the hypoosmotic to the
hyperosmotic solution
 Osmoconformers,
consisting only of some
marine animals, are isoosmotic with their
surroundings and do not regulate their
osmolarity
 Osmoregulators expend energy to control water
uptake and loss in a hyperosmotic or
hypoosmotic environment
 Osmoconformers
 Only
vertebrate that is isotonic to seawater - much
like marine invertebrates


Aquatic vertebrates - gills are chief organs of
excretion/osmoregulation
Kidneys first evolved as osmoregulatory organs in fishes
to remove water (freshwater) or conserve water (marine)
Most marine vertebrates are osmoregulators
 Marine bony fishes are hypoosmotic to sea water
 They lose water by osmosis and gain salt by
diffusion and from food
 They balance water loss by drinking seawater and
excreting salts

(a) Osmoregulation in a marine fish
Gain of water
and salt ions
from food
Gain of water
and salt ions
from drinking
seawater
Excretion
of salt ions
from gills
Osmotic water
loss through gills
and other parts
of body surface
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
Key
Water
Salt
A
different form of osmoregulator
 Freshwater animals constantly take in water by
osmosis from their hypoosmotic environment
 They lose salts by diffusion and maintain water
balance by excreting large amounts of dilute urine
 Salts lost by diffusion are replaced in foods and by
uptake across the gills
(b) Osmoregulation in a freshwater fish
Gain of water
and some ions
in food
Key
Water
Salt
Uptake of
salt ions
by gills
Osmotic water
gain through
gills and other
parts of body
surface
Excretion of salt ions and
large amounts of water in
dilute urine from kidneys
 The
type and quantity of an animal’s waste
products may greatly affect its water balance
 Among the most significant wastes are
nitrogenous breakdown products of proteins
and nucleic acids
 Fish typically produce toxic ammonia (NH3)
rather then less toxic compounds
 Abundance of water to dilute toxic materials
Proteins
Nucleic acids
Amino
acids
Nitrogenous
bases
—NH2
Amino groups
Most aquatic
animals, including
most bony fishes
Ammonia
Mammals, most
amphibians, sharks,
some bony fishes
Urea
Many reptiles
(including birds),
insects, land snails
Uric acid
1 Filtration
Capillary
Filtrate
Excretory
tubule
2 Reabsorption
3 Secretion
Urine
4 Excretion
Animal
Freshwater
fish. Lives in
water less
concentrated
than body
fluids; fish
tends to gain
water, lose salt
Inflow/Outflow
Does not drink water
H2O in
Salt in
(active transport by gills)
Salt out
Urine
Large volume
of urine
Urine is less
concentrated
than body
fluids
Animal
Marine bony
fish. Lives in
water more
concentrated
than body
fluids; fish
tends to lose
water, gain salt
Inflow/Outflow
Drinks water
Salt in H2O out
Urine
Small volume
of urine
Urine is
slightly less
concentrated
than body
fluids
Salt out (active
transport by gills)
 Each
species has a range of environmental osmotic
conditions in which it can function:
o stenohaline - tolerate a narrow range of salinities in external
environment
o euryhaline - tolerate a wide range of salinities in external
environment
• short term changes: estuarine - 10 - 32 ppt,
intertidal - 25 - 40
• long term changes: diadromous fishes
(salmon)
Euryhaline
o organisms like salmon:
o In sea, they drink sea
water and discharge salt
through their gills
o In freshwater, they stop
drinking and produce
large volumes of dilute
urine, gills take up salt




Anadromous: Most of life spent in salt water, returning to rivers or
other freshwater to spawn.
Amphidromous: migrate between salt and freshwater at some
point in the life cycle, but well before final maturation and
spawning
Catadromous: Most of life spent in freshwater, returning to ocean
to spawn.
Diadromous: Blanket category referring to any migration between
salt and fresh water or vice versa
Marine cartilaginous fishes:
o Shark tissue contains a high concentration of urea
o To prevent urea from damaging other organic
molecules in the tissues, they have trimethyl amine
oxide (TMAO)
o Because of high solute concentration in tissue,
water enters the cells (sharks don’t drink)
o Produce concentrated urine