Rockpool Blenny, Hyposoblennius gilberti

Rockpool Blenny, Hypsoblennius gilberti. Fish caught from coastal waters off Ventura, California, October 2017. Length: 10.5 cm (4.1 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Rockpool Blenny, Hypsoblennius gilberti. Fish caught from the Carlsbad Lagoon, Carlsbad, California, October 2017. Length: 11 cm (4.3 inches). Catch, photograph, and identification courtesy of Ryan Crutchfield, Tampa, Florida.

Rockpool Blenny, Hypsoblennius gilberti. Fish caught off the Ocean Beach Pier, San Diego, California, May 2008. Length: 13 cm (5.1 inches). Identification courtesy of Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, California.

Rockpool Blenny, Hypsoblennius gilberti. Fish caught from coastal waters off Encinitas, California, August 2016. Length: 14 cm (5.5 inches). Catch, photograph, and identification courtesy of Ben Cantrell, Peoria, Illinois. Identification reconfirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, California.

The Rockpool Blenny, Hypsoblennius gilberti, is a member of the Combtooth Blenny or Blenniidae Family, that is also known as the Notchbrow Blenny and in Mexico as borracho de poza. Globally, there are sixteen species in the genus Hypsoblennius, four of which are found in Mexican waters, one in the Atlantic and three in the Pacific Ocean.

The Rockpool Blenny has an elongated body that are deepest at the beginning of the dorsal fin and taper gradually to the tail; they are one of the largest blennies. They have an overall green olive coloration with extensive mottling over a tan background and are off-white ventrally. All their fins have the same color as the body but their spines and rays have touches of blue. Their anal fin has a row of small tan dots centered on each ray. Their head is darker in color with 2 prominent oblique bars originating under the eyes. They have the ability to change color to match their surroundings. They have a short head with a pointed snout and prominent small eyes set well above the body; the cirri over the eyes are divided into 7 or more filaments. Their mouth is small and opens at the lower front. Their anal fin has 2 spines and 19 to 21 rays; their caudal fin is rounded; their dorsal fin has 12 spines and 18 or 19 rays without a notch in between and the rays are longer than the spines. Their lateral line terminates above the middle of the anal fin base and their skin is smooth and without scales.

The Rockpool Blenny is a non-migratory coastal species found in intertidal and sub-tidal rocky areas at depths up to 18 m (60 feet). They reach a maximum of 17 cm (6.8 inches) in length. They are somewhat unique being able to survive out on water by consuming oxygen from the atmosphere for significant periods to time. They are diurnal and feed on benthic crustaceans and small crabs. They have strong homing tendencies and typically return to the same tidal pool at low tide. 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. Males are not as territorial or aggressive as other members of the Hypsoblennius genus. They have a lifespan of up to 9 years. The Rockpool Blenny  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 Rockpool Blenny is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Magdalena Bay, Baja California Sur, northward along the central and northwest coasts of Baja.

The Rockpool Blenny is similar in appearance to several blennies but the cirri over its eyes are divided at the base into 7 or more filaments. It also has a unique lateral line that extends above the midpoint of the anal fin. It can be confused with the Bay Blenny, Hypsoblennius gentilis and the Mussel Blenny, Hypsoblennius jenkinsi but both have orbital cirri without numerous branched filaments.

From a conservation perspective the Rockpool Blenny is currently considered to be of Least Concern with stable, widely distributed populations. They too small to be of interest to most and are normally a “catch-and-release.”