Blue Bobo, Polydactylus approximans

Note:  for the first two fish presented below the identifications should be considered as tentative. A correct identification is only possible with a barbel count which was not made with either of these fish.  Although “blue” in coloration there is a remote possibility that one or both are Yellow Bobos.

Blue Bobo, Polydactylus approximans. Fish caught with a cast net off the pier at Puerto Adolfo Lopez Mateos, Baja California Sur, December 2021. Length: 9.0 cm (3.6 inches). Catch courtesy of Ruben Duran, Puerto Adolfo Lopez Mateos, Baja California Sur. Photograph and tentative identification courtesy of Brad Murakami, Surrey, British Columbia, Canada.

Blue Bobo, Polydactylus approximans. Fish caught via a shrimp trawler from coastal waters off Mazatlán, Sinaloa, October 2018. Length: 25 cm (10 inches). Photograph courtesy of George Brinkman, Guelph, Ontario, Canada.

Blue Bobo, Polydactylus approximans. Fish caught off the beach at Punta Lobos, Baja California Sur, May 2006. Length: 30 cm (12 inches).

The Blue Bobo, Polydactylus approximans, is a member of the Threadfin or Polynemidae Family, and is known in Mexico as barbudo seis. Globally, there are twenty species in the genus Polydactylus, of which five are found in Mexican waters, three in the Atlantic and two in the Pacific Ocean.

The Blue Bobo has an elongated compressed bodies and are fairly similar to freshwater catfish. They are bronzy brownish dorsally and transition to silvery yellow ventrally. Their pectoral fins are yellow with the central portion being black. Their head has a short conical snout that overhangs the mouth, large eyes with fatty covers that are well forward, and a modest sized mouth below the snout equipped with teeth in bands on the top jaw. Their anal fin has 3 spines and 13 to 15 rays and a short base; their caudal fin is deeply forked; their first dorsal fin has 8 spines; their second dorsal fin has 1 spine and 12 or 13 rays; their pectoral fins are low on the sides and divided in two parts: the first is low and under the gills with 5 or 6 long free rays and the second is in the upper section with 12 to 15 rays. Their free pectoral rays serve as feelers and scoops in the feeding process. Their pelvic fins are far behind the pectoral fins and slightly preceding the second dorsal fin. They have 26 to 31 gill rakers. They are covered with rough scales. Their lateral line extends into the caudal fin branching into each lobe.

The Blue Bobo is a non-migratory species found over sandy and muddy bottoms in bays, estuaries, and river mouths, and along sandy beaches at depths up to 30 m (100 feet). They reach a maximum of 36 cm (14 inches) in length. They feed on mobile benthic invertebrates. The Blue Bobo 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 Blue Bobo is are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from of the extreme northern portions of the Sea of Cortez.

The Blue Bobo is easily confused with the Yellow Bobo, Polydactylus opercularis (dark blotch on the gill cover; 8 or 9 free pectoral rays; yellow pectoral fin).

From a conservation perspective the Blue Bobo is currently considered to be of Least Concern with stable, widely distributed populations. They are relatively small, not abundant, and of limited interest to most. However, when available they are considered an excellent food fish.