Biodiversity

Saturday, May 06, 2006

MORPHOLOGICAL DIFFERENCES BETWEEN BONY AND CARTILAGINOUS FISH

Chordates (Phylum Chordata) are animals that have a notochord which is a stiffened cartilage rod or a back bone1 Cartilage is a dense connective tissue made of Chondrocytes (cells) embedded within a firm gel-like matrix with no blood vessels.2

Bone is a “hard endoskeletal connective tissue” which has a bone marrow and both the bone and cartilage the derived from the mesoderm.3

Chondrichthyes are cartilaginous fish which include sharks, rays and skates7, 4. They have a large brain which is less dense than the one of bony fish in comparison to their bodies4. Cartilaginous fish don’t have a bone marrow as they don’t have a bone. They produce the red blood cells in the spleen, a specialized Heydig’s organ and the specialized tissue around the gonads4. In comparison the bony fish have a bone marrow where the red blood cells are produced. They also have a special organ called Epigonal organ which is responsible for their immunity needs as their counterparts immune system is taken care of from the bone marrow 4.

Bony fish have external fertilization whereby they lay eggs that are later fertilized outside the body. The fertilized eggs later hatch to young fish, though many of which don’t reach maturity level6. Cartilaginous fish have internal fertilization like mammals and give rise to live small fish (e.g. the ray) or lay eggs (some sharks and skate). 4, 5 Sharks produce either by oviparity (lay eggs), vivparity (born alive) or oviviparity (eggs mature within mother without being fed by the mother) 6. This means of fertilization ensures that all eggs are fertilized as compared to external fertilization where sperm is sprayed on the eggs and can be washed off. The eggs also can be easily predated on6. Also the process of keeping young one in the body enhances their chances for survival of the young. Though internal fertilization has an advantage as compared to the external in terms of security of the young it also makes the Chondrichythes heavy. This makes an advantage to the bony fishes allowing them to move fast.

Bony fishes have an internal organ called a swim bladder that helps them to float5. They used to move to the water surface and gulp air and fill a pouch which served as the first lungs and were used for buoyancy, later developed into a swim bladder. Cartilaginous fish rely on oil stores in their body and have to keep swimming to remain afloat. 6 Bony have the ability to float in one position by the ability to absorb oxygen through their blood system from the gills which fills the swim bladder and this gas can be regulated to determine the height the fish wants to float. This frees the fins and tail for movements other than staying afloat making them fast.

Some sharks like the sand tiger shark normally gulp air from the surface and store it the stomach to maintain buoyancy6. Due to their somehow heavy head they have pectoral fin which helps them maintain balance and also propels them by beating in water.

The bodies of cartilaginous fish are covered by a tough skin covered with dermal teeth which feels like a sand paper called the placoid scales. This helps them reduce turbulence as they move .6 Bony fish have smaller tightly fitting scales overlapping like roof tiles and covered by mucous making more it smooth and slippery7. This makes them agile and move fast. Bonyfish have the ability to float in one position by the ability to absorb oxygen through their blood system from the gills which fills the swim bladder and this gas can be regulated to determine the height the fish wants to float.

Osteichthyes have adapted well and are able to occupy various niches as compared to Chondrichthyes who are restricted to only being either mobile hunters (sharks) or sea bed feeders7.

References:

1. Wikipedia contributors. Chordate [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 15:22 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Chordate&oldid=53007616.

2. Wikipedia contributors. Cartilage [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 21:28 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Cartilage&oldid=51425191.

3. Wikipedia contributors. Bone [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 24, 16:15 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Bone&oldid=49935964.

4. Wikipedia contributors. Chondrichthyes [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 20:22 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Chondrichthyes&oldid=51731653.

5. Wikipedia contributors. Fish [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 18:29 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Fish&oldid=51715687.

6. Wikipedia contributors. Shark [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 20:53 UTC [cited 2006 May 5]. Available from: http://en.wikipedia.org/w/index.php?title=Shark&oldid=51577174.

7. Knight, R. BCB Biodiversity chapter 2 The Conquest of the Water and the Birth of the Vertebrates (Cited 2006 May 5) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_81.htm



VINCENT MUCHAI WAIRIMU

Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190

Email: 2648463@uwc.ac.za

Website:http://www.muchai.iblog.co.za

3 Comments:

  • Your referencing is improving. Since you are using numbers, your references should be in the order in which they appear in the text. All information should be referenced.

    Morphology refers to form and structure, not function.

    By Blogger Gwen, at May 22, 2006 11:32 AM  

  • Hii, Vincent, I learn from your referencing style as Gwen indicated that, its nice.

    By Blogger linette, at May 31, 2006 5:15 PM  

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