Notchfin Blenny

Notchfin Blenny, Entomacrodus chiostictus

The Notchfin Blenny, Entomacrodus chiostictus, whose common Spanish name is borracho aleta mocha, is a species in the Combtooth Blennies or Blennidae Family, known as collectively borrachos in Mexico. This fish is also known as the Rock Blenny. Globally, there are twenty-four species in the genus Entomacrodus, two of which are found in Mexican waters, one in the Atlantic and one in the Pacific.

The Notchfin Blennies have very elongated bodies. 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. 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 one to ten tips, and one pair of slender cirri on their nape. Their anal fin has two 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. Their skin is smooth and without scales.

The Notchfin Blennies are a non-migratory coastal species found in very shallow waters and weed-covered intertidal and subtidal rocky areas (including tidal pools) at depths up to six feet. They reach a maximum length of 7.5 cm (3.0 inches). 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. They are a small shallow-water species with very little is known about their behavioral patterns.

In Mexican waters the Notchfin Blennies are found all waters of the Pacific with the exception that they are absent from Magdalena Bay northward along the central and northwest coasts of Baja, and from 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).

The Notchfin Blennies are too small to be of interest to most and are normally a “catch-and-release.”

Notchfin Blenny, Entomacrodus chiostictus, male. Fish collected from a tidal pool at the Gordo Point Reef, 6 miles north of Puerto Los Cabos, Baja California Sur, November 2007. Length: 6.0 cm (2.4 inches). Identification reconfirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, CA.