Giant Kelpfish

Giant Kelpfish, Heterostichus rostratus

The Giant Kelpfish, Heterostichus rostratus, whose common Spanish name is sargacero gigante, is a member of the Kelp Blenny or Clinidae Family, known collectively as sargaceros in Mexico. This is the only global species in the genus Heterostichus and it is found only in Mexican waters of the Pacific.

The Giant Kelpfish have elongated and compressed bodies. They are cryptically colored and have three different morphologies, red, brown, and green, that closely match their surrounding plant habitat. They also have four different dark melanin patterns which appear to be superimposed and can change rapidly. Their head is elongated and pointed with a small terminal mouth and modest-sized eyes. Their caudal fin is deeply forked and their dorsal fin is very long and continuous with many more spines than rays.

The Giant Kelpfish are found in rocky areas with kelp forests and surrounding plant intertidal habitats at depths up to 50 feet. They reach a maximum length of 61 cm (24 inches) with females being larger and living longer than males. They feed on small crustaceans, mollusks, and small fish. They are found associated with a large number of different plant species as they have the ability to change colors to match their surroundings. Reproduction is oviparous with females depositing eggs into algal nests which are vigorously guarded by males for up to two weeks until they hatch. They are well-developed upon hatching and remain in the planktonic stage in schools within the kelp forest for several weeks. Juveniles develop coloration and become solitary moving to nearshore algae. They have a lifespan of up to five years.

In Mexican waters, the Giant Kelpfish are abundant and found from Magdalena Bay northward along the central and northwest coasts of Baja.

The Giant Kelpfish is very similar to, and can be easily confused with, the Crevice Kelpfish, Gibbonsia montereyensis, the Spotted Kelpfish, Gibbonsia elegans, and the Striped Kelpfish, Gibbonsia metzi, however, all three have rounded caudal fins.

The Giant Kelpfish are utilized by the aquarium trade on a limited basis. They are also retained on a limited basis by subsistence fishermen for food. From a conservation perspective, they are currently considered of Least Concern, primarily due to their wide distribution.

Giant Kelpfish, Heterostichus rostratus. Underwater photo taken in coastal waters off Mission Bay, San Diego, CA, September 2016. Length: 25 cm (10 inches). Photo courtesy of Bob Hillis, Ivins, UT.

Giant Kelpfish, Heterostichus rostratus. Underwater photo taken in coastal waters off Mission Bay, San Diego, CA, September 2017. Length: 30 cm (12 inches). Photo courtesy of Bob Hillis, Ivins, UT.