Topsmelt, Atherinops affinis
The Topsmelt, Atherinops affinis, whose common Spanish name is pejerrey pescadillo, is a species in the New World Silverside or Atherinopsidae Family, known collectively as charales and pejerreyes in Mexico. Although a smelt by name, this fish is not considered a true smelt; its common name is derived from its habit of swimming near the surface. Globally, this is the only species in the genus Atherinops and it is found in Mexican waters of the Pacific.
The Topsmelts have slender elongated and somewhat compressed bodies. They are silvery overall and blue-green dorsally. They have a bright silver stripe with a blue border that runs the full length of their mid-body. Juveniles are translucent white with a midline stripe. They have a pointed head, small eyes, a blunt rounded snout, and a terminal oblique extendible mouth equipped with one row of tiny forked teeth on each jaw. Their anal fin is inserted under the rear of the first dorsal fin and has one spine and 19 to 25 rays. Their caudal fin is forked. They have two separated dorsal fins, the first with 5 to 7 spines and the second with one spine and 8 to 14 rays. Their pectoral fins have 13 rays and reach past the pelvic fin origin. Their pelvic fins are closer to the anus than to the top corner of the pectoral fin base. They have 20 to 25 rounded gill rakers. They do not have a lateral line and are covered with smooth scales.
The Topsmelts are a schooling pelagic species found within estuaries, bays, sandy beaches, rocky areas, piers, and kelp beds at depths up to 85 feet in waters that can range from 5oC (41oF) to 29oC (84oF). They reach a maximum length of 37 cm (14 inches). They can be found in schools of thousands of individuals and are often mixed with sardines. They are active daytime and bottom feeders that consume various kinds of zooplankton. Juveniles consume algae, kelp, and fry larvae. They have the ability to live in waters with very high salt content, for example, in the salt evaporation ponds of the greater San Francisco area which have salt content levels three times that found in normal seawater. On a seasonal basis, they provide “cleaner services” to the California Gray Whales, Eschrichtius robustus removing whale lice when the whales visit Baja California for birthing. Reproduction is oviparous in nearshore habitats with large masses of sticky eggs released by females. These eggs attach themselves to shallow water seaweed and eel grass via means of long filaments and are then fertilized by males. The larvae are planktonic. They have a lifespan of six to nine years.
In Mexican waters the Topsmelts have a limited distribution being found along the entire west coast of Baja and in the upper two-thirds of the Sea of Cortez; they are absent from the southern Sea of Cortez and along the coast of the mainland south to Guatemala.
The Topsmelt is similar to, and can be confused with, the California Grunion, Leuresthes tenuis (first dorsal fin origin over anal fin origin) and the Jacksmelt, Atherinopsis californiensis (large gap between dorsal fins; anal fin origin well behind end of first dorsal fin).
The Topsmelts are a favorite of pier fishermen in California, especially those under the age of ten, where they are caught year-round normally on high tides with baited or unbaited Sabiki rigs. If one fish is hooked, several others will often be hooked on the reel in. Historically they have been targeted by commercial fishermen and caught with purse nets but current interest has diminished and they are now seldom seen in markets. They are an important food source for a wide variety of predators including fish, marine mammals, and sea birds and are known to breach to avoid predation. They are also used as bait on a limited basis. From a conservation perspective they are believed to be common and widespread and to have stable populations, thus are classified as of Least Concern, however, their population trends are unknown. There is some concern that human development will remove the eel grass meadows used as their spawning grounds. They were a staple of Native Americans.
Topsmelt, Atherinops affinis. Underwater photo taken in coastal waters off La Jolla, CA, September 2017. Length: 23 cm (9.0 inches). Photo courtesy of Bob Hillis, Ivins, UT.
Topsmelt, Atherinops affinis. Fish caught off the Oceanside Pier, Oceanside, California, May 2006. Length: 30 cm (12 inches).
Topsmelt, Atherinops affinis. Fish caught off the Oceanside Pier, Oceanside, California, June 2007. Length: 32 cm (13 inches).