Includes all bony fishes
Largest class of all vertebrates
Accounts for 96% of all fish species.
Freshwater and Marine
Skeleton of bone
Single pair of gill openings
Primarily Fusiform shape
Deviate in 3 ways
Laterally compressed: common for fish who
live in dense cover or coral reefs.
Depressed: common in bottom dwelling fish
Example: Sea Moth
Elongated: common in open ocean fish and
eels. Example: Barracuda
Depressed body shape
Most fish species have pigmentation
Chromatophores can contract and
expand to change colors.
Iridescent- Reflective scales
Cave dwelling fish lack pigmentation.
Fish using chromatophores to match
Fish reflects light and matches
Purpose of Coloration
Disruptive coloration- breaks up animals shape
Change color to match surroundings
Advertisement to other fishes
Mate attraction and recognition
Some species produce light through a
chemical reaction process.
Used to attract mates, confuse or deter
predators, or attract prey
Light production occurs in
Photophores- light producing cells
Light-producing bacteria- live in or on the
fish in a symbiotic relationship
Two kinds of fins-
Paired fins- Pectoral and Pelvic
Median fins- Dorsal, Caudal, and anal
Most fins are supported by rays (soft or rigid)
Some species have spiny rays associated
with venom glands.
Example: Stonefish, Lionfish, Scorpionfish
Lionfish, warning colors
Mouth- located on anterior end
Nostrils- used for smell, no connection to
Gills- Single pair of openings, covered by
a flexible plate called Operculum.
Teeth- fused to the jaw bone
Eyes- size and position vary by habitat
and behavior. Deeper = bigger eyes
Scales are thin and flexible
Develop from bone tissue
Scales overlap from head to toe to
Covered by a thin layer of tissue as well
Some bony fishes only have scales on
portion of body, or none at all
4 Types of Scales
Purpose of Mucus
Helps to protect fish from infection
Covers body to conceal scent from
Example: Parrotfish enclose their bodies in
a mucus bubble at night so predators cannot
Some juvenile fish feed on the mucus of
Parrotfish enclosed in
Buoyancy provided by gas-filled swim
Gas volume changes as the fish changes
Average lifespan of fish is 12-20 years.
Larger species typically live longer than
Infections and parasites are common
causes of death in fish.
3 Types of fish Movement
1) Most fish swim with a rhythmic side to side
motion of the body or caudal fin
2) Elongated fish like eels swim using a
serpentine motion. They undulate their body in
lateral waves that travel from head to tail.
3) Other fish, like tuna, have shorter bodies
and swim by moving only powerful and rigid
caudal tail. (fastest)
Most fish reproduce externally by spawning
Females lay eggs and males release sperm
1. Drift in water column
2. sink and remain on bottom
3. Eggs may be sticky and attach to plants etc.
4. Some fish brood eggs in mouth
5. Some bury eggs
Some fish have internal fertilization and are
Seahorse: Females deposit eggs in a pouch on the male’s
The male then releases sperm and the eggs develop inside
The male then gives birth
Some fish are hermaphrodites.
Sequential - Born one sex but change at some point during life
due to social hierarchy/behavior
Synchronous- Have both sperm and egg producing organs at
the same time.
The number of offspring is inversely
related to the chances of the eggs
The larger number of eggs laid means
there is a lower chance of surviving.
The Common Mola lays 28 million eggs in a
The Atlantic Tarpon releases over 100
million every time it spawns.
Various factors may influence breeding
1. Change in duration of sunlight
2. Temperature change of the water
3. Presence of the opposite sex
4. Change in currents, tide, or stages of the
Reproduction is generally cyclic in bony fish.
Some spawn many times a year, while
others spawn only once a lifetime and then
die soon after. Ex: Pacific Salmon
Anadromous- Fish that spend most of their
time in the sea, but breed in rivers.
Catadromous- FW fish that migrate to the
sea to breed.
Hearing- No external opening; inner ear for
equilibrium, detecting acceleration, and
Eyesight- Well developed for some species.
Taste- taste buds inside mouth, responsible for
accepting or rejecting prey
Smell- well developed
Lateral Line- Vibrations
1. Commercial Fishing
2. Recreational fishing
3. Habitat destruction- building dams,
stream diversion, destroy coastal
5. Introduced species
6. Aquarium Collection