Slough Anchovy, Anchoa delicatissima

Slough Anchovy, Anchoa delicatissima. Fish caught from coastal waters off San Diego, Baja California, September 2013. Length: 5.1 cm (2.0 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).

The Slough Anchovy, Anchoa delicatissima, is a member of the Anchovy or Engraulidae Family, that is also known as the Southern Anchovy and in Mexico as anchoa delicada. Globally, there are thirty-five species in the genus Anchoa, of which twenty-three are found in Mexican waters, nine in the Atlantic and fourteen in the Pacific Ocean.

The Slough Anchovy has a moderately elongated body. Their head has a moderate pointed snout with very large eyes, and a large mouth that extends well past the eyes. They are a translucent silvery with a greenish tint dorsally and white ventrally a bright silver stripe that runs mid-body from the head to the tail that is uniform in width and about 75% of their eye diameter. Their anal fin has 20 to 25 rays and originates under the mid-point of the dorsal fin base and is less than two time the length of the dorsal fin base; their dorsal fin has 13 to 15 rays; and, their pectoral fins have 12 or 13 rays. They have 18 to 21 lower gill rakers and 44 to 53 in total.

The Slough Anchovy is a pelagic coastal species found in large dense schools in estuaries and the backwaters of bays at depths up to 50 m (165 feet). They reach a maximum of 12 cm (4.7 inches) in length with females being larger than males. They are filter feeders and consume plankton that is complemented with amphipods, plant material, and polychaetes. In turn they are preyed upon by numerous sea birds and fishes. Reproduction is oviparous and occurs in schools. Each female, on average will broadcast 7,000 eggs which are fertilized externally during the spring and early summer with the adults migrating to specific areas. The eggs are larvae are planktonic. The larvae are known to make nocturnal vertical migrations. They have a life spans of up to three years. The Slough Anchovy 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.

In Mexican waters the Slough Anchovy is a resident of the Pacific Ocean but has a limited distribution being found from Magdalena Bay northward along the central and northwest coasts of the Baja.

The Slough Anchovy is mostly likely confused with the Northern Anchovy, Engraulis mordax (anal fin origin is under the extreme rear of the dorsal fin).

From a conservation perspective the Slough Anchovy is currently considered to be of Least Concern, with stable, widely distributed populations. Their long-term survival has been adversely affected by human coastal developments and pollution. They are of limited interest to most but are utilized by recreational anglers as a live bait on a limited basis. They are also utilized on a limited basis as an indicator of environmental stress.