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Flat-clawed pistol shrimp

Alpheus aequus

A small Pacific marine pistol shrimp known for its modified snapping claw. It produces incredibly loud acoustic shockwaves and leads a cryptic lifestyle.

Taxonomy
Class:Malacostraca
Order:Decapoda
Family:Alpheidae
Genus:Alpheus
Species:Alpheus aequus

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Water Temperature

21 - 26 °C

pH Value

8.1 - 8.4

Water type

Marine

Invertebrate type

Marine shrimp

Adult size

4 cm

Minimum group

>= 1

KH

8 - 12 dKH

Ecological role

Symbiont

Species description

Geographical Origin and Habitat: Alpheus aequus is native to the eastern Pacific Ocean, with populations extending from the Gulf of California south to Peru and the Galapagos Islands. It inhabits coastal coral reefs, shallow lagoons, and rocky rubble flats at depths ranging from 1 to 20 meters, where it constructs complex burrow systems under rocks and sand.
Taxonomy: Belonging to the family Alpheidae and the genus Alpheus. This species is characterized by its asymmetrical claws, though its snapping claw is notably less oversized compared to other members of the genus. Its body is laterally compressed with a short rostrum that covers the eyes, which are positioned beneath the carapace.
Social Behavior: Exhibits a highly cryptic, nocturnal, and burrow-dwelling lifestyle. It is a tireless excavator, continuously clearing sand and debris from its tunnels. It often forms symbiotic relationships with shrimp gobies (such as Amblyeleotris), maintaining the burrow while the goby acts as a sentinel.
Coloration and Sexual Dimorphism: The body coloration is generally pale, ranging from yellowish-tan to translucent grey with subtle banding. The specific epithet 'aequus' refers to the relatively equal proportions of its minor claw compared to its major claw. Sexual dimorphism is not visible externally without microscopic inspection.

Care, breeding and tankmates

Tank Setup: Requires a mature marine aquarium of at least 40-50 liters. A substrate bed of fine sand mixed with coarse coral rubble at least 6-8 cm deep is essential to allow for natural digging and tunnel reinforcement. Always secure rockwork directly to the glass bottom of the tank to prevent structures from collapsing.
Diet and Feeding: An opportunistic omnivore and detritivore. It feeds on organic waste, uneaten fish food, and microfauna. Supplement their diet by target-feeding small pieces of frozen foods (mysis, brine shrimp) or sinking pellets near the burrow entrance using a long pipette or feeding tube.
Water Quality: Demands stable marine parameters: temperature of 21-26 °C, pH of 8.1-8.4, and specific gravity of 1.021-1.025. Extremely sensitive to copper, which is toxic to invertebrates. Proper calcium and iodine levels are necessary to support successful molting and exoskeleton development.
Compatibility and Tankmates: Reef-safe and peaceful toward corals and passive tankmates. It is best kept with symbiotic shrimp gobies. Avoid housing with large, predatory bottom fish such as groupers, hawkfish, large wrasses, or aggressive crabs that could prey on the shrimp when it ventures outside its burrow.
Aquarium Breeding: Breeding in captivity is exceptionally rare. Gravid females carry eggs under their abdomen on their pleopods until they hatch. The released larvae are planktonic and microscopic, and they are typically removed by mechanical filtration or protein skimmers before they can settle.
Risks and Diseases: Molting failure is the most common cause of death, often caused by lack of trace minerals (calcium/iodine) or water parameter shock. The characteristic snapping sound is a defensive mechanism and is completely harmless to the aquarium glass, serving only to ward off intruders.

Geographic Origin and Distribution

Alpheus aequus is native to the eastern Pacific Ocean, with populations extending from the Gulf of California south to Peru and the Galapagos Islands. It inhabits coastal coral reefs, shallow lagoons, and rocky rubble flats at depths ranging from 1 to 20 meters, where it constructs complex burrow systems under rocks and sand.

Origin

Tropical oceans and reefsExtra-Amazon South AmericaNorth America

Invertebrate profile

Diet
Omnivore
The Alpheus aequus is generally considered an opportunistic omnivore that will scavenge for leftover food, detritus, and small organisms. In the home aquarium, its diet should be supplemented with a variety of meaty foods such as frozen mysis shrimp, brine shrimp, and high-quality sinking pellets. Providing a varied diet ensures they receive the necessary nutrients for growth and molting. Feeding them targeted amounts helps prevent starvation while keeping the aquarium clean.
Ecological role
Symbiont
In its natural habitat, the Alpheus aequus serves as a valuable cleaner and scavenger, helping to control detritus and organic waste. By consuming uneaten food and dead organic matter, it plays a critical role in nutrient recycling within the reef ecosystem. Some species within this group also engage in symbiotic relationships with other marine life, providing cleaning services in exchange for food. Their presence indicates a healthy and balanced marine environment.
Shock sensitivity
High
The Alpheus aequus is quite sensitive to sudden changes in water parameters such as salinity, temperature, and pH. Rapid fluctuations can cause severe osmotic shock, leading to stress, failed molts, or immediate death. It is highly recommended to use a slow drip acclimation method over several hours when introducing them to a new aquarium. Consistent water quality and stability are paramount for their long-term survival and health.
Calcium and minerals
Medium
Proper calcium levels are essential for the Alpheus aequus to successfully build and maintain its exoskeleton. Along with calcium, trace elements like iodine and magnesium must be kept at optimal marine levels to facilitate the molting process. A lack of sufficient calcium can result in soft shells, deformities, and ultimately fatal molting complications. Regular water changes with high-quality salt mix usually provide adequate amounts of these crucial minerals.
Molting
Yes
Molting is a vulnerable time for the Alpheus aequus, during which it sheds its old exoskeleton to grow a new, larger one. Following a molt, the invertebrate will hide in the rockwork for a few days until its new shell hardens completely. During this period, they are highly susceptible to predation and physical damage from tank mates. It is best to leave the discarded exoskeleton in the tank, as they often consume it to reclaim valuable minerals.
Reproduction
Oviparous
Breeding the Alpheus aequus in a home aquarium can be challenging due to the complex larval stages and dietary needs of the offspring. These invertebrates often carry their eggs under their abdomen until they hatch into planktonic larvae. Raising the delicate larvae requires specialized rearing tanks and constant supplies of specific microscopic live foods. Although spontaneous spawning is common in well-fed adults, successful rearing to maturity is rarely achieved by casual aquarists.
Compatibility & tankmates
Reef safe with caution
The Alpheus aequus is generally peaceful and can be safely housed with a wide variety of reef-safe fish and corals. Care should be taken to avoid keeping them with large, aggressive fish such as triggerfish, puffers, or large wrasses that might view them as a meal. They are usually tolerant of other peaceful invertebrates, though some territorial squabbles may occur with closely related species. Providing ample hiding spots among live rock will help them feel secure and reduce stress.

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

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Last updated: 06/30/2026
Flat-clawed pistol shrimp (Alpheus aequus) Care Guide & Tank Setup | Atlarium