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Blackfin pacu (Colossoma macropomum) in fish market in Brazil
Courtesy of Thorke A.S. ?stergaard, via Fishbase, BY-NC

About Ray-finned Fishes (Class Actinopterygii): Use by Humans

Most of the fishes eaten by humans are ray-finned fishes, such as salmon, trout, tuna, flounder, catfish, cod, and bass. While some ray-finned fishes are tiny, an ocean sunfish can weigh as much as 5,000 pounds. Including about 29,000 species in more than 400 families, ray-finned fishes provide plenty of options for human consumption. A handful of species are cultivated on fish farms for commerce that totals billions of dollars annually. Ray-finned fishes, such as goldfish and tetras, support a high-value pet commerce as well. Unfortunately, many populations of ray-finned fishes are threatened by overharvesting, introduced species, water pollution, and other impacts to their habitats. While most extinctions have been of freshwater species, ocean species such as tuna have suffered severe declines. Several hundred species of ray-finned fishes are in danger of extinction (endangered), while more than 500 species are vulnerable to endangerment.

The greeneye fish (Chlorophthalmus acutifrons) has large eyes for seeing in the darkness of deep water
Courtesy of Islands in the Sea 2002, NOAA/OER


About Bony Fishes (Superclass Osteichthyes): Senses

Bony fishes have complex eyes that provide color vision, and some are specialized to detect ultraviolet or polarized light. On a fish snout is a smell organ that detects chemicals dissolved in water. Smell is used to sense food or alarm signals sent by an injured fish of the same species. Taste is not necessarily confined to the mouth, with taste buds spread around the heads of bony fishes, or even on their bodies. For bony fishes, sound is a full body experience as it conducts through their bones and fluids. Bony fishes have a sensory system, the lateral line, which we can only dream of. Consisting of small canals holding sense organs on the surface of a fish, the lateral line detects pressure changes, such as water turbulence from moving objects. Without it, bony fishes swimming in a group (school) could not make fast, synchronized movements.

A variety of captured, larval fishes
Courtesy of Estrella Malca, University of Miami, NOAA's Fisheries Collection

About Bony Fishes (Superclass Osteichthyes): Reproduction

The vast majority of bony fishes reproduce sexually. While some bony fishes bear live young, most fish are egg-layers (oviparous). Many small eggs are laid by the female in clumps. Males produce milky sperm that either fertilizes the eggs during mating or after they have been laid. Making an underwater nest is challenging, but some bony fishes do build nests by hollowing out a place in the sand, blowing a cluster of bubbles, or sticking aquatic plants together. A few bony fishes even incubate the eggs in their mouths. Nests are often defended by males, females, or both. Survival of eggs is low, as they make a tasty meal for many predators. Humans enjoy them as the delicacy “caviar.” A single female may lay thousands or even millions of eggs in her lifetime, with only a handful of offspring making it to maturity. Offspring (larva) tend to shelter in different habitats than adults until their bodies mature.

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Reddish gill tissue of a black sea bass (Centropristis striata) showing under the gill flap
Courtesy ofSEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC


About Bony Fishes (Superclass Osteichthyes): Respiration

All bony fishes must intake oxygen and get rid of carbon dioxide for their cells to function. Most bony fishes exchange gases with water using grill-like structures behind the mouth called gills. Gills are reddish because they are infused with blood vessels, which circulate oxygen through the rest of the fish. Some bony fishes swim with their mouths open, allowing water to pass through the gills, while others pump a space behind the gills to pass water over them. Because the concentration of oxygen is lower in water than air, and water is denser, lungs used underwater would not meet oxygen needs. The layers of highly folded membranes in gills create a large surface area for gas exchange. When a fish is taken from water into less dense air, its gills collapse and it gasps for oxygen. Some bony fishes have developed other, innovative ways to get oxygen, including absorption through the skin, digestive organs, or gas bladder.

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