Giant Kelpfish
Heterostichus rostratus

Physical Description

  • Fish with a long and flattened body, shaped like a kelp blade
  • Coloring from light brown to green to purple, depending on the habitat. (In eelgrass, they can be bright green with thin silver stripes. In kelp beds, they can be brown-green like kelp). Can have wavy stripes on their sides
  • Long dorsal fin, almost the entire length of body
  • Deeply forked tail fin
  • Can be up to 24 inches long
  • Juvenile fish can change colors rapidly. Adult females can change colors, but more slowly. Adult males cannot


  • British Columbia to southern Baja California, Mexico
  • Uncommon north of Point Conception


  • Live in shallow water
  • Live in rocky areas, kelp beds, eelgrass, and tide pools
  • Found near piers with heavy kelp growth


  • Females often lay 700 eggs at a time
  • Females deposit eggs into algal nests
  • Males vigorously guard nests for up to two weeks until eggs hatch
  • Larvae are well-developed when they hatch and stay in plankton in large schools for several weeks


  • Small fishes, crustaceans, mollusksĀ 


  • Octopus

Interesting Facts

  • They can quickly change colors during courtship or territorial displays.
  • They can also quickly change colors to camouflage in their environment.
  • Larval kelpfish sometimes school with transparent mysid shrimp.

Sources:; Cabrillo Marine Aquarium;; Seafood Watch

Photo: Kevin Lee

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