Bony Fish Facts

Scientific Names: Osteichthyes, Actinopterygii, Sacropterygii

Two bony fish species: Atlantic sailfish attacking a sardine baitball, Isla Mujeres, Mexico
Rodrigo Friscione / Getty Images

Most of the world's fish species are categorized into two types: bony fish and cartilaginous fish. In simple terms, a bony fish (Osteichthyes) is one whose skeleton is made of bone, while a cartilaginous fish (Chondrichthyes) has a skeleton made of soft, flexible cartilage. A third type of fish, including eels and hagfish, is the group known as Agnatha, or jawless fish. 

The cartilaginous fish include sharksskates, and rays. Virtually all other fish fall into the class of bony fish—including over 50,000 species.

Fast Facts: Bony Fish

  • Scientific Name: Osteichthyes, Actinopterygii, Sacropterygii
  • Common Name(s): Bony fish, ray-finned and lobe-finned fishes
  • Basic Animal Group: Fish
  • Size: From below a half inch to 26 feet long
  • Weight: Well under an ounce to 5,000 pounds
  • Lifespan: A few months to 100 years or longer 
  • Diet: Carnivore, Omnivore, Herbivore
  • Habitat: Polar, temperate, and tropical ocean waters as well as freshwater environments
  • Conservation States: Some species are Critically Endangered and Extinct

Description

All bony fishes have sutures in their neurocranium, and segmented fin rays derived from their epidermis. Both bony fish and cartilaginous fish breathe through gills, but bony fish also have a hard, bony plate covering their gills. This feature is called an operculum. Bony fish may also have distinct rays, or spines, in their fins.

And unlike cartilaginous fish, bony fish have swim or gas bladders to regulate their buoyancy. Cartilaginous fish, on the other hand, must swim constantly to stay afloat. 

School of Blackfin barracuda in the water near the Rangiroa atoll, French Polynesia
 

Species

Bony fish are considered to members of the class Osteichthyes, which is subdivided into two main types of bony fish:

Sarcopterygii is made up of about 25,000 species, which are characterized by the presence of enamel on their teeth. They have a central axis of bone that acts as unique skeletal support for fins and limbs, and their upper jaws are fused with their skulls. Two major groups of fishes fit under the Sarcopterygii: the Ceratodontiformes, or lungfishes, and the Coelacanthiformes, or coelacanths, once thought to be extinct.

Actinopterygii includes 33,000 species in 453 families, found in all aquatic habitats and range in body size from under a half inch to over 26 feet long; one, the Ocean sunfish weighs up to over 5,000 pounds. They have enlarged pectoral fins and fused pelvic fins. Species include Chondroste, which are primitive ray-finned bony fishes; Holostei or Neopterygii, the intermediate ray-finned fishes like sturgeons, paddlefish, and bichirs; and Teleostei or Neopterygii, the advanced bony fishes such as herring, salmon, and perch. 

Habitat and Distribution

Bony fish can be found in waters all around the world, both freshwater, and saltwater. Marine bony fish live in all the oceans, from shallow to deep waters, and in both cold and warm temperatures. Their lifespans range from a few months to over 100 years.

Bony fish include both marine and freshwater species, while cartilaginous fish are only found in marine environments (salt water). An extreme example is an Antarctic icefish, which lives in waters so cold that antifreeze proteins circulate through its body to keep it from freezing. Bony fish also comprise virtually all freshwater species living in lakes, rivers, and streams. Sunfish, bass, catfish, trout, pike are examples of bony fish, as are the freshwater tropical fish that you see in aquariums. 

Below are some other species of bony fish:

Underwater view of mola mola, ocean sunfish, Magadalena bay, Baja California, Mexico


Rodrigo Friscione/Getty Images

Diet and Behavior

A bony fish's prey depends on the species but may include plankton, crustaceans (e.g., crabs), invertebrates (e.g., green sea urchins), and even other fish. Some species of bony fish are virtual omnivores, eating all manner of animal and plant life. 

Reproduction and Offspring

Some bony fish are born sexually mature or become mature shortly after birth; most mature within the first one to five years. the main reproduction mechanism is external fertilization. During the spawning season, females release hundreds to thousands of eggs in the water; and males release sperm and fertilize the eggs.

Not all bony fish do lay eggs: others are live-bearing, and some are hermaphrodites, both male and female in the same fish, or each fish changes over time. Some like the seahorse, are ovoviviparous, meaning the eggs are fertilized in the parent who feeds them from a yolk sac. In seahorses, the parent is the male. 

Evolutionary History

The first fish-like creatures appeared over 500 million years ago. Bony fish and cartilaginous fish diverged into separate classes about 420 million years ago.

Cartilaginous species are sometimes seen as more primitive, and for good reason. The evolutionary appearance fo bony fish eventually led to land-dwelling vertebrates with bony skeletons. And the gill structure of bony fish gill was a feature that would eventually evolve into air-breathing lungs. Bony fishes are therefore a more direct ancestor to humans. 

Threats

Most bony fish species are classed as Least Concern by the International Union for Conservation of Nature (IUCN), but there numerous species that are Vulnerable, Near Threatened, or Critically Threatened, such as Metriaclima koningsi of Africa.

Sources

  • "Bony and Ray-Finned Fishes." Endangered Species International, 2011. 
  • Class Osteichthyes. The Biology Classroom of Mr. Pletsch. University of British Columbia, February 2, 2017.
  • Hastings, Philip A., Harold Jack Walker, and Grantly R. Galland. "Fishes: A Guide to Their Diversity." Berkeley, University of California Press, 2014.
  • Konings, A. "Metriaclima ." The IUCN Red List of Threatened Species: e.T124556154A124556170, 2018. koningsi
  • Martin, R.Adam. Fathoming Geologic Time. ReefQuest Centre for Shark Research.
  • Plessner, Stephanie. Fish Groups. Florida Museum of Natural History: Ichthyology.