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, sometimestiny, or only single opening on throat

Cartilagenous Fish (Class: Chondrichthyes)

The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone.

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 openingson underside of head

A diagram of general Shark morphology

5 gill openings laterally on either side of

head or body