Download Week7-8 - KSU Faculty Member websites

Aquatic Ecology Course
Zoo 374
FISHES
• Main Characters:•
•
•
•
•
All fish live in water
Have gills
Have fins (rays-spines)
Scales (sometimes not exist)
Finfish can be further subdivided into demersal fish
(living on or near the sea bed and including round
and flat white fish, less fat fish) and pelagic fish
(living in mid-water or near the surface and including
oil-rich fish).
Bony Fish (Class: Osteichthyes, Teleosts):
Members of this class characterized by-:
1) Bony skeleton
2) Fins, may be:Paired fins (one fin on each side of the fish), as
pectoral fins and pelvic fins.
Unpaired fins (one fin in all the body) as dorsal, caudal
and anal fins.
3) Scales: are used to determine the fish age. May be cycloid
or ctenoid.
4) Caudal peduncle: as it is thinner the fish becomes faster.
5) Presence of gas bladder
Class (1): Osteichthyes (bony fish = teleosts)
A diagram of general fish morphology
These are generalised diagrams on the shape of bony fish. There are great
number of differences between species. These differences can relate to
body shape, relative size of each fin, Number of rays, colour, shape and
function, as well as internal structure and positioning of the organs.
These diagrams are based on the typical shape of bony fishes.
one gill opening on either side, sometimes
tiny, or only single opening on throat
Cartilagenous Fish (Class: Chondrichthyes)
The Chondrichthyes ro cartilaginous fishes era
,slirtson deriap ,snif deriap htiw hsif dewaj
snoteleks dna ,straeh derebmahc-owt ,selacs
.enob naht rehtar egalitrac fo edam
This Class could be divided into 2 subclasses:
S. Class 1:- Elasmobranchii
(e.g: rays, skates and sharks)
S. Class 2:- Holocephali
(e.g: chimeras = ghost sharks = elephant fish)
General characteristics:
*Animals from this group have a brain weight relative to
body size that comes close to that of mammals, and is
about ten times that of bony fishes, One of the
explanations for their relatively large brains is that the
density of nerve cells is much lower than in the brains of
bony fishes, making the brain less energy demanding
and allowing it to be bigger.
*Their digestive systems have spiral valves, and with the
exception of Holocephali, they also have a cloaca.
* In rays, the pectoral fins have connected to the head and
are very flexible.
*As they do not have bone marrow, red blood cells are
produced in the spleen and special tissue around the
gonads. They are also produced in an organ called
Leydig's Organ which is only found in cartilaginous
fishes.
*A spiracle is found behind each eye on most species.
*Their tough skin is covered with dermal teeth (again with
Holocephali as an exception as the teeth are lost in
adults, only kept on the clasping organ seen on the front
of the male's head), also called placoid scales or dermal
denticles, making it feel like sandpaper. It is assumed
that their oral teeth evolved from dermal denticles which
migrated into the mouth.
S. Class 2:- Holocephali
e.g: chimeras
The chimaeras are characterized by having
tooth plates in their mouths for crushing
hard food and a dorsal spine with a venom
sac at its base. They are found in deep
subarctic and Antarctic waters and are an
evolutionary backwater. Outside the
breeding season they live on the
continental shelf up to 200 metres deep.
S. Class 1:- Elasmobranchii
(e.g: rays, skates and sharks)
Members of this subclass characterized by-:
)1 Have no swim bladders.
)2 Have five to seven pairs of gill clefts opening individually to the
exterior.
)3 Have rigid dorsal fins, and small placoid scales .
)4 The teeth are in several series; the upper jaw is not fused to the
cranium, and the lower jaw is articulated with the upper .
)5 The inner margin of each pelvic fin in the male fish is grooved to
constitute a clasper for the transmission of sperm .
)6 These fishes are widely distributed in tropical and temperate waters.
7) Have a flexible skeleton made of cartilage. For this reason, they are
known as cartilaginous fishes.
8) In Rays and skates are dorsally compressed. Pectoral fin is
modified for swimming.
Class (2): Chondrichthyes (cartilaginous fish)
A diagram of general Ray morphology
5 pairs of gill openings
on underside of head
A diagram of general Shark morphology
5 gill openings laterally on either side of
head or body