Rockwall Clingfish, Arcos erythrops

Rockwall Clingfish, Arcos erythops. Underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2018, November 2018 and January 2019. Photographs courtesy of Ron Woheau, Zihuantanejo. Productive discussions with Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, California, related to the identification of this fish from the above photographs noted are greatly appreciated.

The Rockwall Clingfish, Arcos erythrops, is a member of the Clingfish or Gobiesocidae Family, and is known in Mexico as chupapiedras pejesapo. Globally, there are six species in the genus Arcos, one of which are found in Mexican waters, this species from the Pacific Ocean.

The Rockwall Clingfish has an elongated “tadpole” like flattened body. They are greenish brown in color with an intricate pattern of white, blue and brown spots with tinges of yellow and 2 or 3 broad brown bars across the rear of the body. They have a wide flattened head that has a broad bushy flap for the front nostril and the upper jaw has 2 to 4 pairs of incisors at the front followed by 2 to 4 small canines; the lower jaw and 4 or 5 pairs of incisors followed by 3 or 4 canines on each side. They have a very large sucker on the ventral side. Their anal fin has no spines and 6 rays; their caudal fin has no spines and 7 or 8 rays, their dorsal fin has no spines and 6 or 7 rays; and, their pectoral fin has 21 or 22 rays.

The Rockwall Clingfish is a shallow-water species found in rocky areas within the surge zone at depths up to 15 m (50 feet). They reach a maximum of 5.4 cm (2.1 inches) in length. They feed primarily on algae, small benthic invertebrates and zooplankton. The Rockwall Clingfish  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 Rockwall Clingfish is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found only around the tip of Baja and along the coast of the mainland from the central Sea of Cortez to southern Mexico.

The Rockwall Clingfish is a straightforward identification and within its known range cannot be confused with any other species.

From a conservation perspective the Rockwall Clingfish is currently considered to be of Least Concern with stable widely distributed populations. They are too small in stature to be of interest to most.