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Aquarium of the Pacific - Online Learning Center - Species Print Sheet

Conservation Status:  Safe for Now

Aquatic SpeciesTopsmelt

Atherinops affinis Bony Fishes, marine

Topsmelt Tosmelt in the Aquarium's Amber Forest. | A.Reitsma, Aquarium of the Pacific
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Tosmelt in the Aquarium's Amber Forest. A.Reitsma, Aquarium of the Pacific

Species In-Depth | Print full entry

At the Aquarium

These silvery fish inhabit our Shorebird Sanctuary and the Southern California Gallery’s Amber Forest. Our aquarists prepare a diet of finely chopped mixture of fish, clams, squid, and shrimp or krill for our topsmelt.

Geographic Distribution

Vancouver Island to the Gulf of California, abundant in California.


Although pelagic schooling fish, topsmelt are found in a wide range of habitats depending on the time of year. This species is common in estuaries and can also be seen in shoreline and kelp forest habitats, sandy beaches, and sometimes offshore. They are often found in and around pier pilings and similar structures. They are often seen at the surface and in the upper 9 m (30 ft) of the water column. Many move into estuaries during spring and summer months and to open coasts including bays, rocky areas and kelp beds in the fall and winter. It is not unusual to find them living in salt evaporating ponds.

Physical Characteristics

Topsmelt have a slender, elongate, slightly compressed body with a round blunt snout, a terminal and oblique mouth, and a forked caudal fin. They do not have a lateral line. These pretty little fish are blue-gray to greenish above and silvery below with a bright silver stripe bordered in blue along the full length of the mid-body.


They can reach a length of 36.8 cm (14.4 in), but most are smaller.


Diet varies with habitat and age. Juvenile topsmelt feed primarily on small crustaceans, diatoms, filamentous algae, detritus, midge larvae and amphipods. The main diet of adults consists of various plankton forms, algae, insect larvae, mysids, and copepods. Juveniles and adults often feed near the surface of the water column, but may also forage near the bottom of shallow water that is 2.2 m (6.6 ft) deep.


These fish generally mature in their second or third year. Time of spawning varies with water temperature. The northern area spawning period is between April and October; in the south it occurs from February to June. Both areas have peak spawning in May and June. Topsmelt are primarily nighttime spawners in estuaries and along the open coast.


Topsmelt are schooling fish and may be seen in schools of thousands of individual fish. They are active during the day and become quiet at night. They are often observed “jumping” out of the water when pursued by larger fishes such as jacks or mackerel.


These silvery fish are very tolerant of drastic swings in water salinity and can tolerate anything from fresh water to water with a salt content almost three times that of seawater. They commonly live in the salt evaporating ponds of San Francisco Bay.


This species has a lifespan of six to nine years.


There are many predators that consider this small fish good eating. Among them are larger fishes, California sea lions, harbor seals, Brandt’s and Double-crested Cormorants, Least Terns, and other sea birds.

At one time there was a medium-sized commercial fishery for topsmelt. Most were taken by purse seine or lampara nets and some in gill nets. Today they are taken only incidentally and the small quantities caught are sold fresh. They are rarely seen in markets. In spite of their small size topsmelt are still popular with pier anglers. They are considered good eating by some and they are commonly used as bait.

This species is not on listed as a California species of concern nor is in on the IUCN Red List. However, destructive human impact on eelgrass meadows is caused loss of eelgrass beds, a spawning area favored by topsmelt. Whether topsmelt will be able to adapt by adopting other vegetation is unknown.

Special Notes

While some ichthyologists have separated California’s population of Atherinops affinis into five separate subspecies largely based on geographic location, others believe, as does California Fish and Game, that there is only one species and no subspecies

When Eastern Pacific gray whales, Eschrichtius robustus, are in Baja California, Mexico lagoons, topsmelt serve as cleaning fish for the whales. Normally feeding on marine plants and tiny shrimp, these “cleaner” fish pick at whale lice as an alternative food source.