Fish Most active at night

California Grunion

Leuresthes tenuis

iNaturalist Wikipedia

Witness the silver tide! The California Grunion is a remarkable fish that leaves the ocean to dance on the sand during midnight spawning runs.

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0 Habitats

Quick Identification

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Size

Grows to approximately 15-19 cm (6-7.5 inches) in length; weighs roughly 50-100 grams.

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Colors

Silvery-white underside and sides with a prominent silvery-blue lateral stripe; the back is usually a translucent green or greyish-blue.

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Key Features

Slender, elongated body shape
Distinct silvery lateral stripe along the side
No teeth present in the mouth
Two widely separated dorsal fins

When You’ll See Them

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Activity pattern Most active at night

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Peak hours 10 PM - 2 AM (during spawning runs)

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Season March-August

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Diet Primarily planktivorous, feeding on tiny organisms such as copepods, crustacean larvae, and other zooplankton filtered from the surf.

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Habitat Sandy beaches and shallow coastal waters within the surf zone.

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Where Does the California Grunion Live?

Native to the eastern Pacific coastline of North America, the California Grunion is a true regional specialist. Its core range spans from the cool waters of Monterey Bay in Central California down through Southern California and into the warm, arid coastlines of Baja California, Mexico. They are strictly coastal residents, rarely found more than a few miles from the shore, as they rely on specific intertidal sandy environments for their reproductive cycle.

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2 Countries

120K km² Range

Least Concern Conservation

US United States MX Mexico

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iNaturalist / Verified observation data

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Behavior

The California Grunion is famous for its unique spawning ritual known as a 'grunion run.' Unlike most fish that spawn in the water, Grunion intentionally beach themselves on sandy shores during the highest tides of the month. This behavior occurs at night, following a new or full moon. During these runs, females use their tails to burrow into the wet sand and deposit eggs, while males curve around them to fertilize the clutch before the next wave carries them back to sea.

When not spawning, Grunion are schooling fish that inhabit the nearshore surf zone. They are relatively social and move in large groups to protect themselves from predators. While they are not known for long-range migrations, they do move into slightly deeper waters during the day to avoid visual predators like gulls and then return to the shallows as darkness falls.

Human interaction with Grunion is primarily centered around 'grunion hunting' or observation. In California, these runs attract thousands of spectators. Because they are vulnerable while on the beach, their harvest is strictly regulated by seasonal closures and gear restrictions (only bare hands are allowed) to ensure the population remains stable.

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Camera Tips

Capturing the magic of a grunion run requires a camera setup that can handle low-light conditions and salt spray. For beach-side 'backyards,' use a trail camera with high-quality 'No-Glow' infrared LEDs. This ensures you capture the fish's silver reflections without scaring them (or blinding other beach-goers) with a bright white flash. Mount your camera on a short, weighted tripod or a sand-stake about 6-12 inches off the ground to get a dramatic, low-angle perspective of the fish emerging from the waves.

Timing is everything for this species. Set your camera to record 20-30 second video clips during the predicted peak run times, which usually occur 30 to 60 minutes after the high tide on the second, third, and fourth nights following a full or new moon. Use a high-sensitivity (ISO) setting if your camera allows, as the silver bodies of the Grunion will pop beautifully against the dark, wet sand under infrared light.

Protection from the elements is vital. Even if your camera is 'waterproof,' the salt air and occasional rogue wave can be corrosive. We recommend placing your camera inside a clear, salt-resistant housing or wiping the lens and seals with fresh water immediately after your session. Aim the camera toward the 'wash zone' where the waves reach their highest point on the sand, as this is where the highest density of spawning activity occurs.

Frequently Asked Questions

California Grunion are most active late at night, typically between 10 PM and 2 AM. Their famous 'runs' on the beach occur during the highest tides following a new or full moon.

You cannot attract Grunion with food; they are only 'attracted' to specific sandy beaches during spawning cycles. If you live on a coastal property in Southern California, ensuring your beach is dark and free of artificial light will encourage them to spawn there.

California Grunion eat zooplankton, including small crustaceans and larvae. They are filter feeders that find their food in the nutrient-rich surf zone.

They are very common along the suburban coastlines of Southern California, including beaches in Los Angeles, Orange County, and San Diego, wherever sandy shores are accessible.

Unlike the similar Topsmelt or Jacksmelt, the California Grunion has no teeth and its first dorsal fin begins well behind the origin of its pelvic fins.

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