California Grunion Fish “Leuresthes Tenuis”

grunion fish

Last updated on July 28th, 2022 at 12:58 am

The grunion fish is a small fish that lives in the coastal waters of California and Mexico. They can grow up to six inches long, but they’re usually only one or two inches. These fish congregate on the shoreline during high tide at night for about five hours before returning back out into deeper water where the water is still low.

Origin of the California grunion fish

The California Grunion fish, Leuresthes tenuis (formerly known as Citharichthys) is a species of fish that has been seen in coastal waters from southern California to Baja. The common name derives from an old belief among Californians that these silvery fish come ashore and “grind” themselves to spawn on the beach. For this reason, they are often called “sandfish”.

The grunion season runs from April or May through July each year. The fish come ashore and lay their eggs in damp sand during that period of time when evening tides reach unusually high water levels due to a full moon cycle.

Studies performed by the Scripps Institution of Oceanography in La Jolla, California have shown that grunion spawn on average twice a month.

The Common Grunion is generally found at depths between 0 and 30 feet (0–15 meters), but can occasionally be encountered as deep as 40 feet (12 meters). They are typically seen along sandy beaches or in shallow surf zones.

The most Common Grunions found along the California coast are females, and they can produce from 500 to 1000 eggs during each spawning event.

The fertilized eggs hatch after about two days into a tiny larval fish called an “alevin.” These young grunions remain near shore for one to three weeks, until they are strong enough to swim out into deeper water.

Species profile

grunion fish

The grunion is a type of small fish that lives along the coasts of California, Oregon, and Baja. The larvae are born in the ocean but return to nest on land during high tide. They do this because they need water only for spawning and not feeding – since their parents supply them with food from time to time while they are pregnant.

Lutjanus Jocu - Dogtooth Snapper Fish

The grunion season is also linked to the lunar cycle as well, which means it can be predicted based on the month and date of the year.

Grunion fish are born in the ocean and return to spawn on land, but they do not actually feed when there. They come up onto shore during high tide because that is when their parents will give them food while they’re pregnant. The largest spawning will take place during a full moon in July or August with smaller occurrences happening at other times throughout the year.

These fish eggs are highly nutritious for humans, meaning they are a high-value item for locals.

How to catch grunion fish

The best way to catch them is at night, right before the tide starts going out, when they will be on the beach looking for a place to spawn. When you see their white bellies flashing in and out of the water it’s time to cast your line with some bait.

Since the grunion fish will be spawning on the beach, it’s best to avoid catching them at this time. If you do catch one during their mating season, gently lay your net down and leave them alone. After they’re done with their mating ritual, they’ll return back out into deeper water where the water is still low.

Color and appearance

Grunion fish are silvery-gray to brown in color and have scales on their dorsal side. They can grow up to three inches long, with males generally being larger than females.


Grunion fish live in the sand and surf zone of beaches. They are most active during high tide or when waves break onshore, feeding on small invertebrates that wash ashore. Their habitat is limited to a thin strip between the waterline and where they can reach with their head above the surface level at low tide without being exposed to predators. They bury themselves in the sand with only their suckers exposed to hold on during rough weather.

Synchiropus Splendidus (Mandarin Dragonet)


Grunion fish are typically around six inches long, but they can grow to a maximum of eight inches.

Life cycle

grunion fish

Grunion fish spawn from December through June on or near sandy beaches. They are most abundant in the months of March, April, and May.

The grunion runs at night to avoid predators during its vulnerable spawning phase as it swims upstream to deposit eggs in a moist sandbank that is about one meter deep. The males will turn their white bellies up to the sky and emit a sticky milky substance that clings to their bodies and is readily consumed by hungry shorebirds.

The eggs are laid in large masses numbering as many as 50,000 at a time. The grunion has evolved this defense mechanism for protection from predators such as seagulls or raccoons that like to eat the eggs.

The grunion will return back to sea and then immediately die after spawning, leaving behind their young as a food source for shorebirds.

Grunion fish are not commercially available in markets or restaurants because they only spawn once every year- which is why it’s important to make an effort when observing this interesting fish.

Are they peaceful or aggressive?

Grunion fish are generally a peaceful species. They can be aggressive towards other types of fish, but it is not unheard of for them to breed with non-grunion species in the wild without any aggression from their partner.

In captivity, grunion will sometimes show aggression or try to escape if they feel threatened by an unfamiliar person or by a tank mate that is larger than them.

Grunions are also known to be aggressive towards humans in the wild because they mistake their fingers for food when people touch them; and because of this, it has been advised not to pet grunion unless you can clearly see their tail protruding from the sand.

General care information

grunion fish

What they eat

Grunion fish eat plankton, insects, and crustaceans. However, they can also feed on other small animals like earthworms that live in the sand of a beach. They are known to scavenge for food near animal carcasses as well.

Clark's Clownfish "Clarkii Clownfish"


The grunion typically lives with other fish in a tank. They are usually kept as pets in tanks above the size of 20 gallons, but larger than that is necessary to meet their needs. In addition, they need good water quality and space for swimming freely. The best tank mates for the grunion include small-tooth tetras like the popular neons.

Water condition

The grunion is a fish that spawns in the surf, which means it needs to live near or on beaches. There are many factors that affect these spawning grounds and water conditions. One of the biggest things affecting their habitat is how much freshwater flows into salt water during high tide cycles. Another factor would be sand quality because they need soft sand to bury their eggs in. A third factor would be the quality of water, which can affect spawning rates and even the species that live there along with it.


grunion fish

The grunion’s breeding season is from April to October. During this time, the males move upstream in order to spawn with females who are ready for mating. The process begins as the female starts digging away at the sand and searching for food under rocks or shells on the coastline; meanwhile, an excited male swims by her side waiting for his chance to mate. The female grunion digs a small hole in the sand and deposits her eggs there before she covers them up again, taking care not to leave any traces behind.

The males then proceed upstream for their mating ritual of “sneaking” or “grunting”. They grunt when they find an unfinished nest with eggs, and the female grunion will respond by grunting back. If she is not ready to mate at that time or does not want any more males around, she’ll push out sand from her hole with force in order to discourage him.

After mating, male grunion fish will die while females return downstream to lay their eggs again about a week later.

The eggs hatch as soon as they are covered by the sand, and early larvae grunion fish spend time in their nest until they’re ready to swim upstream for other mating opportunities or food sources. The young grunion fish return downstream again when winter starts approaching. They continue this cycle of swimming upriver as adults and returning downstream as larvae until they reach adulthood.

Lawnmower Blenny Fish (Salarias fasciatus)

Grunion Fish are the only fish that can predict an earthquake! They come to shore by the hundreds just before a big quake and then scatter afterward into deeper water. This is because these small silvery fish use electric currents from below for navigation purposes in their natural habitat of sandy ocean bottoms where there is no light.


The lifespan of a grunion fish is an average of six years and the oldest recorded specimen was 16 years.

Parasites and diseases

Grunion fish are an anomaly with regards to parasites and disease because they have very few. This is probably due in part to their diet of crabs, shrimp, clams, mussels or snails – all animals that harbor a lot less potential for parasite transmission than many other sea creatures. While not completely immune to diseases themselves, grunion fish will only suffer from a handful of them. Consequently, they don’t usually die from illnesses or parasites and disease but rather by being eaten by other animals or getting caught in nets.


Some of the predators of grunion fish are seabirds, seals, and sea lions. Other creatures that may prey on them include the California Sea Lion, White Shark, Bottlenose Dolphin, Harbor Seal, and Bald Eagle.

Does it make good pets?

No. Grunion fish are not domesticated and cannot be kept as pets despite their placid disposition; they reproduce in the wild, so keeping them in captivity would do more harm than good to the species.