Lethabo

im 22 years old, female doing my honns in ecological informatics at csir(pretoria)

Name:
Location: pretoria, gauteng, South Africa

i completed my Bsc (microbiology physiology) degree in 2005 at University of Limpopo, now im doing my honns in ecological informatics at university of the western cape.

Tuesday, May 16, 2006

MORPHOLOGICAL DIFFERENCES BETWEEN CARTILAGINOUS AND BONY FISH

Bone fishes also referred to as Osteichthyes-osseous tissue is a hard endoskeletal (internal support structure of an animal) connective tissue. Bones give the body posture structures support and also help in facilitating movement (1). Bony fishes are characterised by a relatively stable pattern of cranial bones and rooted teeth. The head and pectoral girdles are covered with large dermal bones and the eyeball is surrounded by a sclerotic ring of four small bones. They also have an operculum, which helps them to breathe without having to swim (4).

Cartilage is a type of dense connective tissue and it is composed of cells called chondrocytes. Chondrocytes are dispersed in a gel-like ground substance called matrix (2). Cartilage is a vascular (contains no blood vessels) and nutrients which are diffused through the matrix. Cartilage is mostly found in the joints, the ear, nose, rib cage and in the throat. Cartilages provide a framework for fish which do not have bones (2). The cartilaginous fishes are also referred to as Chondrichthyes which have jaws with paired fins, paired nostrils, scales, two-chambered hearts and a skeleton made of cartilage(3). Cartilaginous fishes have a tough skin which is covered with dermal teeth also called placoid scales or dermal denticles which make the fish feel like sandpaper (3).

Cartilaginous fishes do not have any bone marrow; the red blood cells are produced in the spleen and special tissue around the gonads. In the bony fishes the red blood cells are produced in the bone marrow like in humans. Cartilaginous fishes have a special organ where red blood cells are produced called Organ of Leydig and it is only found in the cartilaginous fishes. Another unique organ is named epigonal organ, and plays a role in the immune system (3).

Cartilaginous fishes have a relative brain which relative brain weight comes close to that of mammals, and is about ten times of bony fishes of the same size. The bony fishes have a relative brain size to be compared with the brain size of humans. One of the explanations why cartilaginous fishes have such large brains is because they are using much less energy. The density of nerve cells in cartilaginous fishes are much lower than in the brain of bony fishes, making it less energy demanding and allows it to be bigger(3).

Bony fishes have various types of calcified tissues: dentine, enamel (or enameloids) and bones. Endochondral bone of the bony fishes begins as a cartilage then it later turns to a bone (4). Cartilaginous fish gets calcium from a cartilage called hyaline (3).

Bony fishes get most of their calcium from the bones but the cartilaginous fishes get their calcium from hyaline articular cartilage. Basically bony fishes consist mostly of a cartilage when the fish is still young the bone only develops when the fish starts to grow so even the bony fish use cartilage because cartilage is much more flexible than bones. Cartilaginous fishes are lighter in weight than the bony fishes which are much heavier for example Marlin (5) which weighs up to 820 kg.

References:

1. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 20:02 PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Bone
2. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 21:28 PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Cartilaginous
3. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 20:22 PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Cartilaginous_fish
4. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 12:50 PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Bony_fish
5. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 15, 09:47 PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Marlin

Lethabo Mosomane
CSIR
Pretoria
0001
Tel: 27 12 841 2133
Fax: 27 12 842 3676
mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

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