Topsmelt, Atherinops affinis
Topsmelt, Atherinops affinis. Fish caught with a cast net from coastal waters of Puerto Adolfo Lopez Mateos, Baja California Sur, October 2018. Length: 25 cm (10 inches).
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).
Topsmelt, Atherinops affinis. Underwater photography taken in coastal waters off La Jolla, California, September 2017. Photograph courtesy of Bob Hillis, Ivins, Utah.
The Topsmelt, Atherinops affinis, is a member of the New World Silverside or Atherinopsidae Family, and is known in Mexico as pejerrey pescadillo. 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 Ocean.
The Topsmelt has a slender elongated and somewhat compressed body. 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 1 spine and 19 to 25 rays; their caudal fin is forked; their first dorsal fin has 5 to 7 spines; their second dorsal fin has 1 spine and 8 to 14 rays; their pectoral fins have 13 rays and reach past the pelvic fin origin; and, 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 are covered with smooth scales. They do not have a lateral line.
The Topsmelt is a schooling pelagic species found within estuaries, bays, sandy beaches, rocky areas, piers, and kelp beds at depths up to 26 m (85 feet) in waters that can range from 5oC (41oF) to 29oC (84oF). They reach a maximum of 37 cm (14 inches) in length. 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 lifespans of between six and nine years. The Topsmelt is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Topsmelt is a resident of Mexican waters of the Pacific but has 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).
From a conservation perspective the Topsmelt is currently considered to be of Least Concern with stable, widely distributed populations. There is some concern that human development will remove the eel grass meadows used as their spawning grounds. They are a favorite of pier fishermen in California, especially those under the age of 10, 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 were a staple of Native Americans. They are also used as bait on a limited basis.