Rockweed Gunnel, Apodichthys fucorum

Rockweed Gunnel, Apodichthys fucorum. Fish caught from a tidal pool in Brookings, Oregon, January 2020. Length: 7.7 cm (3.0 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.

The Rockweed Gunnel, Apodichthys fucorum, is a member of the Gunnel or Pholidae Family that are also known as simply Rockweeds and the Fucus Blenny and in Mexico as espoionoso de marea zacatero. The Pholidae Family has fifteen species placed in three genera, two of which within the Apodichthys Genus, with only this species found in Mexican waters of the Pacific Ocean.

The Rockweed Gunnel has a long, thin eel-like body. They are a translucent uniform green, yellow or red color and have the ability to change colors to match the color of the algae in which they reside. They have striking bright yellow eyes. Their anal fin is rounded and has 1 spine and 32 to 38 rays and is about equal in length to the snout and half the length of their dorsal fin, their caudal fin is rounded, their dorsal fin is long with 83 or 84 spines, their pectoral fins are small and about the same length as the eye diameter, and they lack pelvic fins. They have 8 to 11 gill rakers. They are covered with small circular scales. They have a pair of large eyes on top of their head and a large broad mouth equipped with numerous small teeth.

The Rockweed Gunnel is a demersal species that is found within the intertidal zone within brown algae of the Ficus Genus covered rocks at depths up to 9 m (30 feet). They are found in large groups during the summer months. They reach a maximum of 23 cm (9.1 inches) in length. They have the ability to breathe air and can survive for up to twenty hours out of water. They migrate on incoming tides and consume algae, copepods, small crustaceans, and various mollusks. In turn they preyed upon by larger fish including the Staghorn Sculpin, River Otters, Great Blue Heron, and other marine birds They cover themselves with rocks and algae during low tide episodes to avoid predation. Reproduction is oviparous with adhesive eggs that are guarded by the parents with planktonic larvae. The Rockweed Gunnel 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 Rockweed Gunnel is most likely confused with the Kelp Gunnel, Ulvicola sanctaerosae (lacks both pectoral and pelvic fins).

In Mexican waters of the Pacific Ocean but has a limited distribution being found from Punta Escarpada, Baja California, northward along the central and northwest coasts of Baja.

From a conservation perspective the Rockweed Gunnel has not been formally evaluated. They are small in stature and of interest to most. Family members date to Miocene Period, 5.3 million years ago.