› Fishes are dated back to over 480 million
years
› Fish evolved in fresh water
 Now fish live in ALL water areas – fresh and
salt
› Fish are the dominant, free-swimming
animals of the seas.
› Diet:
 Some are herbivores (eat plant material)
 Others are carnivores (eat meat material)
› The structure of the body is designed for
ease of movement
 This has enabled fishes to live in most parts of
the world's water bodies
› Come in all shapes and sizes
› Active life style:
 Some are free swimming,
 While others rest on the bottom of the sea
 Fish Anatomy
› Fins
 Made up of stiff rays covered by skin.
 Some may be jointed
 Some separate near the edge of the fin.
 Functions :
 Each fin on a fish is designed to perform a specific
function.
 Fish Anatomy
› Fins
 Dorsal fin: lends stability in swimming, controls roll
 Ventral fin: lends stability in swimming.
 Caudal fin: main propelling fin, provides thrust and
controls direction
 Anal fin: lends stability in swimming, increase speed
 Pectoral fins: Locomotion and side to side movement,
acts as rudder and brakes or as feet (mudskippers)
 Skin
› Made of collagen and blood vessels.
› The skin of fish is divided into two layers, the
Epidermis (outer) layer and the Dermis.
 The Epidermis is made of epithelial cells,
 Constantly shed and replaced with new ones.
 Between the epithelial cells are slime cells
 Produce mucous secretions that form the very
important protective covering (slime coat)
 The dermis lies under the epidermis
 Swim Bladder
› Helps maintain buoyancy in the water.
› A sac inside the abdomen that contains gas.
 Scales
› Scales do not stick out of a fish
› The scales overlap
› Form a protective flexible armor
› Capable of withstanding blows and bumping
 Lateral line system
› Def—a series of scales, which connects with a system
of canals containing sensory cells and nerve fibers
› It runs in a semi-line from the gills to the tail fin
› Seen as a band of darker looking scales running along
the side
› VERY important sensory organ in fish
 It can detect minute electrical currents
 Also functions to help the fish identify its surroundings.
 Swimming (Two types)
› Cruisers: Swim continuously in search for food,
such as the tuna.
› Burst Swimmers: stay relatively in the same place
(most reef fish)
 Internal Body Temperature
› Cold blooded (exotherms)
 Derive their body heat from their environment
and conform to its temperature
 Three Modes of Reproduction:
1. Oviparous–
 Lay undeveloped eggs,
 External fertilization (90% of bony fish), Internal
fertilization (some sharks and rays)
2. Ovoviviparous
 Internal development- without direct maternal
nourishment
 Advanced at birth (most sharks + rays)
3. Viviparous
 Internal development- direct nourishment from
mother
 Fully advanced at birth (some sharks, surf perches)

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In fishes, oviparous is most common
Parental care:
› Parental care is very rare as most fish are broadcast
spawners, but there are a few instances of parental
care.

Methods of Parenting
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Egg Scatters- scatter eggs on bottom
Nest Builders- arrange protection for eggs
Egg depositors- selectively place eggs
Mouthbreeders- house eggs in mouth
Egg buriers – bury eggs
Livebearers- give live birth
 Respiration
› Gills
 Located under the gill covers.
 Five gill slits and four gill arches.
 Gills are actually mounted/located on gill arches
 Circulation
› Heart only has two chambers, in contrast to our heart
which has four.
› Heart only pumps blood in one direction.
› A very simple closed-circle circulatory system.
 Digestion
› Some have a spiral valves in intestine
(shark)
 Slows food for better absorbtion
› Most have complete system
 Excretion
› Oily liver to help with water retention, salt
levels and excretory purposes
 Sensory
› Fish can sense light, chemicals, vibrations and
electricity.
› Senses (in addition to lateral line)
 1) Vision:
 Vision underwater poses many special problems. The
most significant is the small amount of light
 Vision is limited to a few yards at best

Senses, cont.
› 2) Smell
 Used in the location of food
› 3) Hearing
 It has been shown that fish can hear, but not very
well
› 4) Taste
 Taste buds in fish are located in the mouth and also
in the skin covering the head, body fins, and lips.
› 5) Touch
 Nothing of importance

Senses, cont.
› 6) Chemicals:
 Some fish (such as sharks, rays, eels, and salmon) can
detect chemical levels as low as 1 part per billion.
› 7) Vibrations:
 Do have ears located within their bodies
 Also have lateral line system that actually lets them feel
their surroundings.
› 8) Electricity:
 Sharks and rays posses special organs for detecting
electrical potential [voltage].
› Kingdom Animalia
› Phylum Chordata (Subphylum Vertebrata)
› Fish Classes:
 Modern fish are divided into three classes.
1. Superclass AGNATHA
2. Class CHONDRICHTHYES
3. Class OSTEICHTHYES
› The most "primitive" of the fishes;
› Lack a jaw and a bony skeleton.
› Very flexible
› Smooth, scaleless skin and are soft to the
touch.
› In place of the jaws is an oral sucker
› Many are highly predatory, attaching to
other fish by their suckerlike mouths,
› Found in both fresh and salt water and
some are anadromous
 Def: living in both fresh and salt water at
different times in its life cycle
› The hagfish has no eyes, while the lamprey
has well-developed eyes.
› Cartilaginous and fibrous skeleton
› Ex: Hagfish and Lamprey
Class Chondrichthyes
› Members include the sharks, skates, rays,
and ratfish.
› Have cartilaginous skeleton, but their
ancestors were bony animals.
› These were the first fish to exhibit paired
fins.
› Pelvic fins in males are modified (claspers)
used in copulation
› Chondrichthyes lack swim bladders,
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Internal fertilization
posses 5-7 gill arches (most have 5).
Exposed gill slits
They have cartilaginous upper and loosely
attached lower jaws with a significant array of
teeth.
Their skin is covered with teethlike denticles
which gives it the texture and abrasive quality
of sandpaper.
Separate sexes with paired gonads
Cloaca
All modes of reproduction
Class Ostieichthyes
› Comprise the largest section of the
vertebrates, with over 20,000 species
worldwide. This compares to 51,000 total
vertebrate species.
› They are called bony fish because:
 Their skeletons are calcified,
endochondral (start out as cartilage)
 Makes them much harder than the
cartilage bones of the chondrichthyes.
› Have great maneuverability and speed,
› Have highly specialized mouths equipped
with protrusible jaws
› Pharyngeal jaws for chewing, grinding,
crushing
› Contain a swim bladder to control
buoyancy.
› Operculum covers gills
› Live in most marine and freshwater
habitats on earth.
› Ex: perch, bass, bluegill, flying fish, sea
horse, clown fish, catfish