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Explore the rich history, unique characteristics, and diverse body shapes of Osteichthyes, also known as "Bony Fish." Learn about crossopterygians, the coelacanth, and various physical characteristics such as body shapes, fins, and skeletal structures. Delve into the fascinating world of bony fishes, their colors, scales, and specialized organs.
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Class Osteichthyes • Largest number of species of all classes of vertebrates, more than 23,500 species. • Cold-blooded • Bony fishes share several distinguishing features: • a skeleton of bone, scales, paired fins, one pair of gill openings, jaws, and paired nostrils.
History • Primitive fishes date back to the Cambrian period - 550 million years ago. • The Devonian period (360 to 400 mya) is known as the "Age of Fishes" because of the abundance and diversity of fishes that appear during this period.
Crossopterygians • Scientists thought that all Crossopterygians were extinct. In 1938, however, a living member of this group, the coelacanth was discovered off the S. African coast.
The Coelacanth • Lobe-finned fishes Courtesy of Dinofish.com
Physical Characteristics Size: Largest: Ocean Sunfish (mola- mola) Smallest: dwarf gobi (0.3 in) Mola-Mola can get to be 13 ft and weigh 3,300 lbs.
Physical Characteristics Body Shape:
Physical Characteristics: Body Shape • Most bony fishes have a fusiform (rounded and tapering at both ends) body shape. • This body shape reduces drag and requires a minimum amount of energy to swim. • Bony fish forms deviate from the fusiform body shape in three directions: • Compression • Depression • Elongation.
Laterally Compressed Body Shape • A laterally compressed body shape is common in bony fishes that live in dense cover or within coral reefs. The compressed body is laterally flattened.
Depressed Body Shape • A depressed body shape is common in bottom-dwelling bony fishes. • Examples: Goosefishes, batfishes and flat fishes
Elongated Body Shape • Elongated body shapes are common in open ocean fishes and eels. • The elongated body is horizontally lengthened. • The morays eels are good examples of fishes with an elongated body shape. Lamprey.
External Anatomy • Highly maneuverable fins supported by bone rays.
Fins • Fishes have two kinds of fins: • paired fins (pectoral and pelvic) • median fins (dorsal, caudal, and anal) • Except in the lungfishes and the coelacanth, fins lack bones. • Some bony fishes have soft, flexible fin rays. • Other bony fishes have spiny, rigid fin rays.
Fins • Dorsal finsprevent rolling, used for stabilization • Pectoral finshelp steer, scull backwards • Pelvic finshelp in stopping quickly, aid in stabilizing • Anal finsprotect uro-genital area (often have spines), further stabilize • Caudal fin for propulsion (tail)
Caudal Fins • Fishes with truncate or rounded caudal fins are usually strong, but slow, swimmers. • Many continuously swimming fishes have forked caudal fins. • Fishes with lunate caudal fins tend to be the fastest fishes and maintain a rapid speed for long durations.
Skeletal Structure • Complex bony skeleton composed of spines (in fins), ribs and vertebrae.
Body Covering Cycloid& Ctentoid scales “Denticles” Placoid scales Overlapping scales gives the fish greater flexibility
Cycloid or Ctenoid Scales • Most bony fishes have cycloid or ctenoid scales. • As they grow, cycloid and ctenoid scales add concentric layers. • Cycloid scales are circular and smooth. • Ctenoid scales have a characteristic toothed edge. They are most common on fishes with spiny fin rays.
Placoid Scales • These scales are found on sharks and are really just small teeth that cover the body. • On sharks placoid scales are known as “denticles”.
Body Covering Ganoid scales are thick and non-overlapping and are composed of bone overlaid with an enamel-like substance called ganoin. These scales are adapted for protection.
Lateral Line • Function: detects the slightest water movements. Also aids in fish schooling. • This special sense organ lies in tiny pits along both sides of the body.
Coloration • Pigment is mostly contained in cells called chromatophores. • Reflective cells called iridocytes can change color rapidly. • Coloration may serve as camouflage: • Most species of fishes are countershaded. • Some fishes show disruptive coloration, a camouflage in which the color pattern of the animal contradicts the animal's body shape. • Some fishes rely on coloration for species recognition and sexual distinction. • Color warns other fishes: • “I will defend my territory” • “I am poisonous”
