Halfmoon Sea Chub
Medialuna californiensis

Physical Description

  • Perch-like body shape
  • Tail fin shaped like a half moon (hence their name)
  • Rounded head with a small mouth and a blunt nose
  • Dark blue to blue-gray backs, fade to light blue/silver bellies
  • Offshore chubs are bluer, inshore more blue-grey
  • Dark spot just above the gill opening 


  • Vancouver Island, British Columbia to Gulf of California, Mexico
  • Most common south of Point Conception


  • Commonly high in the water column
  • Depths of 9-130 feet
  • Over rocks, kelp, or oil rigs


  • Kelp, red algae, and green algae 
  • Opportunistic carnivores that will eat sponges, anemones, and small invertebrates when they encounter them


  • California sea lions, seals, larger fish, marine birds, and bald eagles

Interesting Facts

  • Their coloration allows them to camouflage with the surrounding open water. Their silver bellies blend into the surface reflection as lower fish look up at them, and they are bluer when they are offshore in bluer water. 
  • Because they feed on kelp, their presence in kelp forests helps control kelp growth, and they are important to the health of the overall forest.

Sources: Aquarium of the Pacific

Photo: Matthew Meier

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