Notes on Marine Fishes

Marine Fishes

Ichthyology: study of fishes

Vertebrates are chordates that have four principal characteristics:

• They have a single, dorsal, hollow nerve cord
• They have gills or pharyngeal, slits
• They have a notochord
• They have a post-anal tail

Fishes are the oldest living vertebrates

Types of Fishes

• Jawless Fish (Agnatha)



• Cartilaginous Fish (Chondrichthyes)



• Bony Fish (Osteichthyes)
• Characteristics:
• Bony fishes have bony skeleton
• They usually have ctenoid or cycloid scales, which are made of bone. Some bony fishes lack these scales.
• Ctenoid scales: contains tiny spines
• Cycloid scales: smooth
• Bony fishes have a flap of tissue and bone plates called operculum.
• The operculum protects the gills of the bony fish.
• Bony fishes have jaws that protrude outward from the mouth, which gives more jaw flexibility.
• Many bony fishes have a swim bladder that allows them to adjust to sinking and rising. 
• Some bony fishes can change color with the help of chromatophore cells on the skin.
• Majority of the marine-fishes are bony fishes

Key Terms:

Anadromous fishes: most of their lives are spent in the ocean, but these fishes migrate to fresh water to breed

Catadromous fishes: most of their lives are spent in the fresh water (rivers), but they breed at the sea.

Oviparous: animal that releases the eggs

Ovoviviparous: animals that produces eggs that will hatch inside the female animal right before birth

Viviparous: live-bearers; eggs will develop inside the mother, while the embryo derive nutrition from its mother.

Marine Biology
Marine Fishes - Back to SG Learn Online