Chapter 8
Feeding
 Most fishes are carnivores.
 plankton feeders
 demersal feeders
 open water predators
 Bony fishes – teeth can be
found in jaw, roof of the
mouth, on gill rakers, and in
pharynx
 Cartilaginous fishes – teeth
only on jaw margin
Gill rakers & arches
Digestive System




mouth
pharynx
esophagus
stomach
 J-shaped or elongated
 intestine
 anterior pyloric caeca
secretes digestive
enzymes
 receives inputs from
pancreas and liver
 spiral valve
 cloaca/anus
Circulatory System
 Fish have a two-chambered heart.
 Deoxygenated blood is pumped to the gills where gas
exchange occur.
Circulation and Heat Exchange
 Most fish are
poikilothermic.
 Few large sharks and bony
fish can maintain core
body temperature slightly
higher than their
environment.
 rete mirabile (‘wonderful
net’)
 adaptation for inhabiting
colder waters
Respiratory Anatomy
 Fish exchange O2 and CO2 through paired gills.
Cartilaginous fishes
Bony fishes
Respiratory Anatomy –
Cartilaginous vs. Bony Fishes
Cartilaginous Fishes
 Most swim continuously.
 First pair of gill slits is
modified into spiracles.
 Usually 5 gill slits – may have
6 or 7.
Bony Fishes
 Have a single common gill
chamber.
 Covered by an operculum
Respiratory Anatomy
 Covered by an
operculum
 Gill arches
 Gill filaments
 Lamellae
 Gas exchange occurs by
simple diffusion
 Countercurrent system
of flow
Osmoregulation
 regulation of the
body’s internal salt
balance
 Bony fish
 Body fresher than




seawater
Drink seawater
Salt excreted by kidney
Small amount of urine
Chloride cells
 Cartilaginous fish
 Rectal gland
 Urea in blood
 Absorb water through
gills
Nervous System
 Fish possess a central nervous system, consisting of a
brain and spinal cord.
 Variation exists. Proportional size of the lobes reflects the predominant
movement and feeding behaviors of particular species. (i.e. the largest area of
the lamprey brain is the cerebellum and medulla which indicates the fishes
reliance on grasping with its jaw and attaching to its food).
Fish Senses
 Smell – use sensory cells in olfactory sacs on both sides
of the head. Each sac opens to the nostrils or nares.
 During dissection, note the large portion of the forebrain devoted to smell particularly in
the shark.
Fish Senses
 Taste – Taste buds can be found on the mouth, fins,
skin, lips, and barbels of fish.
Fish Senses
 Sight – used by most fishes
 Unlike terrestrial vertebrates, fish eyes focus by moving the lens closer or
farther away from the subject
 Shallow water species have color vision
●
Sharks and deeper water
species may have little color
vision, but see best in
contrasting light situations
●
Some have a nictitating
membrane that can cover the
eye from the bottom to
reduce brightness or offer
protection
Fish Senses
 Touch – fish possess a lateral line consisting of canals
in the skin and in the bone or cartilage of the head
that connect to neuromast cells that are sensitive to
vibration.
Fish Senses
 Hearing – perceive sound
waves with their inner ears
 Use fluid filled canals on
either sides of the brain
 Some fish amplify sounds
using their swim bladder
 Involved in balance – use ear
stones or calcified otoliths
that rest on sensory hairs
Fish Skeleton
Shark Skeleton
Reproduction
 Sexes are usually separate.
 Some fish are hermaphroditic, but usually still
reproduce with other individuals.
 Some fish are sequential hermaphrodites – individuals
begin life as one gender and later change into the
other.
Sexually dimorphic sockeye
salmon (male on bottom)
Simultaneous Hermaphrodites
 Fish in the Salmon and Sea bass families.
Protygynous sequential hermaphroditism
Protandrous sequential hermaphroditism
Initial phase: initial
males and females
Terminal phase: males
Fish Reproductive Anatomy
 Jawless and bony fish – separate urogenital opening for
urination and gamete release
 Cartilaginous fish – duct leads from reproductive
organ to the cloaca
http://www.marinebiodiversity.ca/shark/english/skull5.htm
Reproductive behavior
 Timing of reproduction controlled by sex hormones
released into blood stream.
 In response to maturation of gametes or to
environmental cues
 Potential mates come together.
 Courtship
 Fertilization – may be internal (most cartilaginous
fish) or external (most bony fish)
 Some fish tend eggs or brood nests (usually males)
Early Development
 Oviparous – large number of immature eggs are laid
at a single time. Larval fish hatches quickly, but still
retains and absorbs yolk sac.
 Ovoviviparous – female retains eggs inside her
reproductive tract for protection

Intrauterine cannibalism
 Viviparous – produce embryos that absorb nutrients
through the walls of the mother’s reproductive tract
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