Associated Smithsonian Expert: G. Dave Johnson, Ph.D.

Smithsonian Ichthyologist and Curator of Fishes, Dr. David Johnson

Photo by Smithsonian Institution

In 1970, following service as a naval officer on a hydrographic survey ship and ten months as reptile keeper at the Houston Zoo, Texas-born Dave Johnson entered the Marine Biology program at Scripps Institution of Oceanography. He had no definite idea about what he was going to do, except that he wanted to be a Marine biologist and thought that whales and porpoises were really cool. In his second year, he took Dick Rosenblatt’s course, "Biology of Fishes," and entered a world of diversity that he had been largely unaware of. He never looked back. Within a matter of weeks he knew exactly what he wanted to do. He became a systematic ichthyologist, and set out on a life full of discovery, problem-solving, and interactions with the most engaging, interesting, and, wonderfully eccentric people that he could ever imagine. Dr. Johnson is Curator of Fishes and Research Scientist with the Division of Fishes at the Smithsonian National Museum of Natural History. His ichthyological research is concerned with the systematics and early life history of teleost fishes, particularly acanthomorphs, with a central focus on comparative anatomy, ontogeny, phylogenetic reconstruction and classification.

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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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Not balloons, but gas bladders removed from fish
Courtesy of Algirdas at the Lithuanian language Wikipedia


About Bony Fishes (Superclass Osteichthyes): Locomotion

Because water offers more resistance than air, it can be energy-intensive to move through it. Bony fishes overcome resistance by moving their bodies, tail, and fins in wavelike motions, generating force against the water. Swimming technique varies, depending on a fish's lifestyle. Long bony fishes, such as eels, move their whole body in wavelike motions that allow them to move forward or backward, maneuvering into small spaces. Bony fishes that need more speed, such as trout, move just the back half of their bodies, making them faster but less maneuverable. Long-distance swimmers, such as tuna, maintain a rigid body with the tail (caudal fin) and tail connector (peduncle) doing all the motion. Some bony fishes use their paired side fins (pectorals), such as puffers who swivel them back and forth. Many bony fishes have a sac-like structure (gas bladder) that allows them to keep the right buoyancy by inflating or deflating it with gases.

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