Notchfin Blenny, Entomacrodus chiostictus

Notchfin Blenny, Entomacrodus chiostictus. Underwater photographs taken in Zihuantanejo Bay, Guerrero, January 2019 and November 2019. Photographs and identification courtesy of Ron Woheau, Zihuantanejo.

Note:  Productive discussions and a review of the majority of the photographs above and the confirmation of their identities courtesy of Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, California.

The Notchfin Blenny, Entomacrodus chiostictus, is a member of the Combtooth Blennies or Blennidae Family, that is also known as the Rock Blenny and in Mexico as borracho aleta mocha. Globally, there are twenty-four species in the genus Entomacrodus, of which two are found in Mexican waters, one in the Atlantic and one, this species, in the Pacific Ocean.

The Notchfin Blenny has a very elongated body. They are olive brown in overall color with thick dark bars on their sides and transition to off-white ventrally. They have a longitudinal row of square black blotches along the middle of their flank. They also have thin brown lines on their snout, lips, and cheeks. The front of their body is covered with small dark spots and the rear is covered with white spots and flecks. They are dimorphic with males are more darkly colored than females. They have a short blunt head with a rounded overhanging snout, and eyes set on top of the head. Their mouth is small, opens at the front, and is equipped with one row of comb-like teeth on each jaw and a pair of canines on the lower jaw that are used for defense. They have simple cirri over their front nostril, eye cirri with 1 to 10 tips, and 1 pair of slender cirri on their nape. Their anal fin has 2 spines and 15 to 17 rays, their caudal fin is rounded, and their dorsal fin has 12 spines and 14 to 16 rays with a deep notch in between. They have 14 to 20 gill rakers. Their lateral line is arched over the pectoral fin and their skin is smooth and without scales.

The Notchfin Blenny is a non-migratory coastal species found in very shallow waters and weed-covered intertidal and sub-tidal rocky areas (including tidal pools) at depths up to 1 m (6 feet). They reach a maximum of 7.5 cm (3.0 inches) in length. They are highly territorial and will vigorously defend their habitat against intruders. They are diurnal and feed on benthic crustaceans including small crabs. Reproduction is oviparous in distinct pairs with the females depositing eggs in protected areas. The eggs are sticky and adhere to the walls of the shelter; they are then fertilized by the males who guard them for two to three weeks until they hatch. The Notchfin Blenny is a small shallow-water species that has been 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 Notchfin Blenny is a resident of all Mexican waters of the Pacific Ocean with the exception that they are absent from Magdalena Bay, Baja California Sur, northward along the central and northwest coasts of Baja, and in the extreme northern portions of the Sea of Cortez.

The Notchfin Blenny is fairly easy to identify due to the deep notch between the spines and rays of it dorsal fin. It is similar to the Bay Blenny, Hypsoblennius gentilis (narrow rows of alternating brown and white blotches on flank), the Foureye Rockskipper, Dialommus macrocephalus (very slender elongated body), and the Mussel Blenny, Hypsoblennius jenkinsi (row of white round spots on lower flank).

From a conservation perspective the Notchfin Blenny is currently considered to be of Least Concern with stable, widely distributed populations. They are too small to be of interest to most.