types of fishes scales

types of fishes scales

• 1.
  Scales of fishes a small rigid plate that grows out of the skin  a part of the fish's integumentary system  produced from the mesoderm layer of the dermis  which distinguishes them from reptile scales.  The same genes involved in tooth and hair development in mammals are also involved in scale development.
• 2.
  Functions of Scales Provideexternal protection to its body as scales are tough & slippery. Help to protect a fish from scrapes, parasites and other external injuries. provide flexibility because they are all attached at only one point.
• 3.
  Types of Scales •There are four different types of fish scales. 1. Cosmoid scales 2. Ganoid scales 3. Placoid scales 4. Leptoid scales • Cycloid scales • Ctenoid scales
• 4.
  1. Cosmoid scales •Very rare scale type, but no doubt common in extinct species e.g; Crossopterygians • Limited today to the primitive lobefin and lungfish • Cosmoid scales evolved from placoid scales fusing together • This is because cosmoid scales have two base plates and similar external spines are composed of vitrodentine.
• 5.
   Inner layerof the scale is made of lamellar bone  On top of this lies a layer of spongy or vascular bone  a layer of dentine-like material called cosmine.  These scales grow along with the fish.
• 6.
  2.Placoid Scales • Alsocalled denticles, are similar in structure to teeth • Found on sharks, skates and rays. • Formed of a rectangular base plate that is embedded within the skin of the fish. • The interior of the scale is a pulp that receives blood from the fish's vascular system • outside is made of an enamel-like substance called vitrodentine.
• 7.
  •Placoids have asharp ridge down the center of the scale made of vitrodentine. Placoids do not grow with the fish
• 8.
  Ganoid Scales usually rhomboid in shape.  They are modified Cosmoid scales  consist of a bony basal layer, a layer of dentine, and an outer layer of ganoine.  can be found on gars, bichirs andon and reed fishes.  Rare among modern fish.  do not overlap instead fit together like pieces of a jigsaw puzzle  They also grow with the fish, not only in length, but in width and thickness as well.
• 9.
  4. Leptoid scales Foundon higher-order bony fish like Asian arowana. As they grow they add concentric layers. They come in two forms:  Cycloid Scales  Ctenoid Scales
• 10.
  Cycloid scales  Cycloid(circular) scales have a smooth texture and are uniform, with a smooth outer edge or margin.  They are most common on fish with soft fin rays, such as salmon and carp. Ctenoid scales  Ctenoid (toothed) scales are like cycloid scales,  except they have small teeth or spinules called ctenii along their outer or posterior edges.  Because of these teeth, the scales have a rough texture.  They are usually found on fishes with spiny fin rays, such as the perch-like fishes.  Salmon fish
• 11.
  References: • www.wikipedia.org • www.australianmuseum.net •www.ehow.com • www.earthlife.net