Download Fish Notes - Sardis Secondary

VERTEBRATES
Vertebrates belong to the subphylum Vertebrata of
the Phylum Chordata. Vertebrates include fish,
amphibians, reptiles, birds, and mammals.
Remember that all chordates, including vertebrates,
Share four main characteristics which include:
a) dorsal nerve cord (spinal cord / brain)
b) notochord (backbone)
c) gill slits or pouches (gills / lungs)
d) post-anal tail (kept by most vertebrates)
The backbone, which surrounds the spinal cord, is
made up of bony segments called VERTEBRAE.
The vertebrates have an endoskeleton which has two
main parts:
1.) Axial Skeleton – It is made up of the vertebral
column, skull, and rib cage. It supports the body and
protects the spinal column, brain, and other internal
organs.
2.) Appendicular Skeleton – It is made up of the
appendage bones and the wide flattened girdles to
which they are attached. It is attached to the axial
skeleton.
Other vertebrate characteristics include a welldeveloped brain and sensory organs, a closed
circulatory system, and a multi-chambered heart.
FISHES
 Inhabit nearly every type of aquatic
environment on Earth
Characteristics of all fish:
1. breathe using gills
 as a fish takes water in through its
mouth, water passes over the gills
and then out through slits at the side
of the fish
2. have 2 chambered hearts
 one chamber receives oxygen-poor
blood from the body tissues
 the other chamber pumps blood
directly to the capillaries of the gills,
where oxygen is picked up and
carbon dioxide releases
3. reproduce sexually
 fertilization & development is external
in MOST fishes
 eggs & sperm can be released
directly into the water, or deposited in
more protected areas
4. highly developed sensory systems
 have eyes that allow them to see
objects & contrast between light and
dark in the water, but the amount of
vision varies among fishes
 fishes can be grouped into 4 classes:
Super Class Agnatha:
- jawless fish
- have smooth, scaleless skin & long
cylindrical body
- have cartilaginous skeleton,
- no vertebral column
- only vertebrates to retain notochord
through all stages of their life
1. Class Cephalaspidomorphi: lampreys
 most are parasites that hitch rides
on their hosts,
often killing its host
as it sucks out its
victim’s body fluids
2. Class Myxini: hagfish
 bottom dwellers that spend most of
their time hiding in mud and sand
 scavenger that eats fish that are
already dead or dying
3. CLASS CHONDRICHTHYES: (cartilage
fish)
- includes sharks, rays, & skates
- have hinged jaws and paired fins
- have internal fertilization
- skates deposit fertilized eggs on
the ocean floor
- some female
sharks & rays
carry developing
young inside their
bodies
- have a lateral line system that enables
them to sense objects and changes in their
environment
- is a line of fluid-filled canals running
along the sides of a fish that enable it
to detect movement and vibrations in
the water
Sharks:
- would sink if they did not swim
continuously because they are denser than
water (also suffocate if water not moving over
gills)
- have tough, leathery skin that is covered
with PLACOID SCALES
- mouth is lined with 6-20 rows of sharp
teeth which continuously form and move
forward to replace lost or worn teeth
- have a screw-like membrane, called a
SPIRAL VALVE, which extends through the
centre of the intestine. It slows the
movement of food to give more time for
digestion
- have a large, oily liver that can make up
nearly 20% of its total body weight (liver oil
is lighter than water and gives sharks
buoyancy)
4. CLASS OSTEICHTHYES (bony fish)
- includes:
i)ray-finned fish (salmon, guppies, tuna)
- fan-like moveable fins made of thin
membrane supported by bony rays
- use their paired pectoral and pelvic fins to
steer, brake, move up and down, and even
swim backwards
- skin is covered with thin, round scales,
called CYCLOID SCALES, which overlap like
shingles (can determine age by counting rings
of scales)
- mucus covers scales giving the fish a
slimy surface
- have a thin-walled sac in the abdominal
cavity filled with gas called a SWIM
BLADDER
 dissolved gases in the blood diffuse
into & out of the swim bladder
 as the bladder fills up, the fish rises
and when it deflates, the fish sinks
- have four pairs of gills & each set of gills
is covered by a protective flap of tissue
called an OPERCULUM
- Unlike sharks, can
pump water
through their gills
even when
motionless
- also have a lateral
line system that
detect changes in pressure and vibrations in
water
- have two pairs of nostrils as well as
chemical receptors scattered over their head
and body. Smell usually gives fish their first
clues about food, mates, and enemies
- most have separate sexes and fertilization
is external
ii) lobe-finned fish (lungfish & coelacanth)