Hippopus Clam: Hippopus hippopus

Bear Paw Clam, Horse's Hoof Clam, Strawberry Clam

Family: Cardiidae Hippopus Clam, Hippopus hippopus, Bear Paw Clam, Horse's Hoof Clam, Strawberry Clam, and China ClamHippopus hippopusPhoto © Gerald Heslinga, Indo-Pacific Sea Farms

The Hippopus Clam is a hardy aquarium specimen, and prized for its very colorful and decorative shell!

The Hippopus Clam Hippopus hippopus may not have a super flashy mantle, but among the giant clams, it wins the contest for the most beautiful shell. The mantle on most specimens is generally a dull green/brown to gray with faint cream markings, but the shell has a frilled shape and can be colorful. The shell is usually a grayish white with attractive markings of various colors. In the wild, however, larger specimens are often so over-grown with hitchhiking organisms, that their markings are simply not visible,

This species is commonly known as the Hippopus Clam, but with its decorative shell, it is also known as the Bear Paw Clam, Horse's Hoof Clam, and the Strawberry Clam. It is one of two species of giant clams that are known as "Hippopus Clams." The other is its close relative, the China Clam H. porcellanus, which is not common in the aquarium industry. Both of these giant clams have traditionally been harvested for their meat, and are also highly prized for their shells.

The shell of H. hippopus is thick, heavily ribbed, and adorned with rows of round strawberry red markings. Thus the name Strawberry Clam. The descriptive common names, Bear Paw Clam and Horse's Hoof Clam, come from the sturdy stature and large size of these clams. Horse's Hoof comes from the look of the shell when the clam is closed and sitting on its byssal opening. The broad base of the closed valve is shaped like a horse's foot.

The China Clam H. porcellanus has a thinner shell that is less deeply ribbed. It also lacks much of the strawberry coloring. Being quite large, the shells of either species can be cleaned, bleached and polished for a number of uses. Common uses include ornaments, night lights, and soap dishes, but a favorite use for the large decorative Hippopus Clams are as serving bowls.

This is a hardy giant clam that will generally reach about 16 inches (40 cm) in captivity, though it has been recorded up to almost 18" in the wild. It's easy to acclimate and keep in the home aquarium, as long as it is given enough space to grow.

In the wild, the number of Hippopus Clams have been greatly reduced due to over collection. However, today the H. hippopus is cultivated in captivity. It is supplied as a food source and for its shell, but it is also available to the aquarist. The demand from aquarists has raised interest in producing colorful varieties of all the giant clam species, and some beautiful green specimens of the Hippopus are now being aquacultured.

For more about keeping Hippopus Clams, see:
Giant Clam Care: Caring For Tridacnid Clams

Geographic Distribution
Hippopus hippopus
Data provided by GBIF.org
  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Bivalvia
  • Order: Veneroida
  • Family: Cardiidae
  • Genus: Hippopus
  • Species: hippopus
Hippopus Clam - Quick Aquarium Care
  • Minimum Tank Size: 100 gal (379 L)
  • Aquarist Experience Level: Beginner
  • Temperament: Peaceful
  • Temperature: 74.0 to 83.0° F (23.3 to 28.3° C)
  • Size of organism - inches: 17.7 inches (45.01 cm)
  • Diet Type: Omnivore
  • Suitable for Nano Tank: No

Habitat: Distribution / Background

The Hippopus Clam Hippopus hippopus was described by Linnaeus in 1758. They are found in eastern Indian Ocean at Myanmar and east to the Fiji and Tonga Islands, in the north as far as southern Japan and then south to the Great Barrier Reef, New Caledonia and western Australia, Other common names it is known by are Bear Paw Clam, Horse's Hoof Clam, and the Strawberry Clam.

There are only two clams in this genus, the other being the China Clam or Porcelain Clam H. porcellanus. They differ from the Tridacna genus, as they are able to close their shell completely and their mantle does not hang over the shell’s edges. Both species are currently listed on the IUCN Red List as least concern (LC). They have long been hunted for food and souvenir shells and may be absent in some areas.

They inhabit shallow waters, or even intertidal zones, as deep as 19.7 feet (6 meters). As the H. hippopus grows, it loses its byssal gland and relies solely on its size and weight to hold its place. Because of this, adults are usually found lose on reef flats, grassy areas of reef flats, sandy substrate, slightly muddy substrate, gravel or coral rubble. Juveniles use their byssal gland to stay lightly attached to the harder surfaces until they are over 5” (14 cm). At that time they start depending on their weight and eventually lose the byssal gland. These clams don't burrow so the shell is exposed and is usually found with various organisms hitching rides.

Hippopus Clams feed on small particulate matter such as phytoplankton, zooplankton and other nutrients from the water. Predators are small pyramidellid snails that bore into their tissue and feed on their bodily fluids.. While this is less of a problem in the wild, it is more of an issue in enclosed systems.

  • Scientific Name: Hippopus hippopus
  • IUCN Red List: LC - Least Concern - May be extinct in some regions. Now aqua-cultured


Hippopus Clams will grow to around 16" (40 cm) in captivity, however almost 18" (45 cm) has been recorded in the wild. They are fast growing giant clams, becoming sexually mature around 5 1/2" 14 cm) when they are about 2 years of age. They are all born males then turn female as needed. Aquarists have kept this clam for decades, but giant clams have been known to live over 200 years in the ocean.

Giant clams have a soft, laterally compressed body that is enclosed in an elongated shell. The shell consists of two hinged parts. The hinge of the Hippopus Clam is usually more than half the shell's length on juveniles, and may grow to as much as 2/3's of the shell length on adults. The hinge has an opening called the "byssal opening," where a muscular foot attaches to a hard surface. The shell halves are symmetrical to each other, and this clam can close its shell completely.

They have no head, but their soft body consists of a mantle forming an outer wall that encloses a visceral mass containing the body's organs. The mantle has a siphon, also called the intake siphon, that is is a fleshy tube-like structure. The intake siphon is used to direct water flow into the mantle cavity and across the gills.

Hippopus hippopus by Gerald Heslings of IPSFThe mantle of the Hippopus Clam is usually a dull olive-green to yellowish-brown, and sometimes gray, with some faint spots or thin stripes in cream, white or gold. The mantle may not be as flashy as those of the the Tridacna clams, but some greens are now being aqua-cultured that are truly beautiful.

The Hippopus Clams really stand out when it comes to their shells. They are thick and heavy, and ruffled with as many as 14 folds. Usually only about 5 to 8 of these folds are strongly pronounce, however. The folds create many nooks and crannies which offer protected living areas for various little critters.

Their shells are usually grayish-white overall, though some may be faintly shaded in yellow or orange. But unlike the Tridacna genus, the shells of the Hippopus have attractive markings of various colors. The H. hippopus is uniquely adorned with rows of round strawberry red markings, and thus it is also known as the Strawberry Clam. However, in the wild larger specimens are often so over-grown with hitchhiking organisms that their markings are simply not visible.

Some characteristics of the H. hippopus clam:

  • The mantle is dull green/brown to gray with some faint stripes or spots of gold, cream or white..
  • The mantle doesn't extend past the edge of the shell.
  • Shells are thick and very heavy.
  • There are small tube shaped structures on the shells, not found on any other giant clam.
  • Shells will have reddish blotches
  • Inhalant siphon does not have tentacles.
  • Byssus gland is very narrow and the opening is bordered with interlocking teeth.
  • As the clam grows it loses its byssal gland and relies solely on its size and weight to hold its place.

The Hippopus Clams differ from the Tridacna clam species by the mantle, which on these clams doesn't extend past the edge of the shell as it does on the Tridacna clams. They can also be distinguished by the mantle color and the shell color.

Comparing Hippopus Clams to other species of Giant Clams:

  • The mantle on species from the Tridacna genus extends way past the edge of the shell, but not on Hippopus species.
  • Tridacna clams cannot completely close up and most have larger byssal openings.
  • Unlike Tridacna clams, Hippopus shells are thick and very heavy.
  • The China or Porcelain Clam H. porcellanus is similar, however, the inhalant siphon of the China Clam has large, branching tentacles.
  • The China Clam H. porcellanus has a thinner shell that is less deeply ribbed than H. hippopus.
  • The China Clam also lacks much of the strawberry coloring found on the H. hippopus.
  • Size of organism - inches: 17.7 inches (45.01 cm) - They commonly reach about 16" (40 cm) in captivity, however 18" has been recorded in the wild. They are sexually mature around 5.5" (14 cm).
  • Lifespan: 200 years - May live decades in captivity, but can live over 200 years in the wild.

Difficulty of Care

The Hippopus Clam is considered the absolutely most hardy of the giant clams, especially now that they are aqua-cultured. This large clams is not as sensitive as other clams, however it still needs a stable water flow, light that is in the 6K to 10K range, and a tank that can handle its weight and size. It can be kept by beginners as it is very easy to keep in a home aquarium if provided with enough room for growth. This clam will need good water quality maintained and moderate to strong lighting, but it will require little else in the way of care.

If a healthy clam is obtained and proper lighting provided, this clam is quite hardy and relatively easy to keep. Obtain a specimen, preferably over 4," and you'll have a hardy clam that can easily acclimate to your tank. Clams under 4" are not as hardy and do not ship well. When first obtained, inspect the clam's shell for predators that can be removed. It is important to make sure it is not being irritated nor fed upon by other organisms.

These clams adjust to their new surroundings in time, and will become very hardy, especially once they reach about 12" long. But to keep them healthy, avoid wide fluctuations in light, water flow, reef water parameters (calcium, magnesium, etc.), and salinity. They need a low to moderate water flow, and are not tolerant of sudden increases in light intensity.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Beginner

Foods and Feeding

Most clams fulfill their nutritional requirements by filter feeding and absorbing dissolved organic compounds from the water. Giant clams have gone even further than this, using zooxanthellae to manufacture food for themselves. They receive the majority of their nutrition from their zooxanthellae, yet research has shown that all Giant Clams that are under 4" do not have enough mantle tissue to provide enough space for zooxanthellae to keep the clam alive.

It is generally believed that mature giant clams do not require feeding in the aquarium. Whether additional feeding is required is still debated. Some hobbyists believe they should be fed, going on the assumption that they are filter feeders like other clams. Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and a minute amount of nitrate that is at least 2 ppm. They will not thrive at a level of 0 nitrates.

Four ways clams make food for themselves:

  • These clams have large amounts of zooxanthellae that live in their tissues. With plenty of light this algae will make too much food for themselves and the extra carbon and glucose is given to the clam (similar to most reef corals).
  • The actual zooxanthellae themselves can be eaten by amoeboid cells within the host clam if needed.
  • Giant clams have the ability to absorb nutrients like ammonia, nitrate and phosphates from the water.
  • Giant clams are filter-feeders, straining fine particulates like phytoplankton, zooplankton and detritus from surrounding waters with their specialized gills.

Since smaller Hippopus Clams are dependent on phytoplankton from various sources when younger, they need to be spot fed several times per week. If they are under 2" to 4" they may need daily feedings. Feed them micro-foods designed for filter feeders such as a yeast-based suspension that has been mechanically whisked, live phytoplankton or commercially prepared micro-foods like 'marine snow' or 'reef snow’.

In the wild, once they are older, they basically make their own food on days when the light is not strong enough. Since this shouldn't be an issue in captivity with good lighting, they do not need to be fed phytoplankton foods unless they are in an aggressively skimmed tank. If they are in a tank with lots of fish, once they are 12" they really do not need to be fed directly.For more information about the feeding process of Hippopus Clams see What Do Clams Eat.

  • Diet Type: Omnivore - Nutrition is obtained through filter-feeding of phytoplankton, zooplankton and detritus along with lighting and the marine algae, zooxanthellae.
  • Flake Food: No - Will not eat this.
  • Tablet / Pellet: No - Will not eat this.
  • Live foods (fishes, shrimps, worms): Some of Diet - Clams under 4" will need live phytoplankton to thrive.
  • Liquid Foods: Some of Diet - Marine snow or other phytoplankton substitutes, especially if there are no fish. Lighting and the marine algae, zooxanthellae, make up the rest of the food.
  • Meaty Food: Some of Diet - Most food comes from lighting and the marine algae, zooxanthellae.
  • Feeding Frequency: Daily - Feed clams daily up to 2" in size, several times per week up to 4", and weekly up to 8." At 12" and larger, do not feed them if there are plenty of fish in the tank. Do not feed if there are plenty of fish at 12"

Aquarium Care

Hippopus Clams are quite hardy and relatively easy to keep if a healthy clam is obtained. With careful attention paid to water parameters, proper lighting, good filtration it will thrive. Stable tank conditions are required to keep the Hippopus Clam healthy. Do typical water changes of 10% biweekly, 20% a month, or 5% weekly. It has been noted that 5% weekly water changes replenish many of the needed additives.

Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and a minute amount of nitrate. Along with regular water changes the following parameters are important in keeping your Hippopus Clam long term. Adding large doses weekly is not recommended. Daily doses or adding to top off water is best:

  • Calcium: Calcium is the main building block for clams and should be present in the water at levels of at least 280 mg/L for growth to occur. Seachem's calcium additive works at 385. More rapid, natural growth is seen when calcium is in the range of 400-480 mg/L.
  • Strontium: Strontium is incorporated in the shell along with calcium and should also be provided for optimum growth.
  • Iodine:The addition of iodine to the aquarium will also enhance growth and color. Use caution, as iodine spikes have been known to kill them. Add iodine with top off water or dose daily, but not at one time in a big weekly dose.
  • Nitrate: They require some nitrogen for proper growth. They will not thrive at a level of 0 nitrates. Nitrate can be added if levels are extremely low, but be careful as nitrates should never exceed 2 mg/L. Provide a minute amount of nitrate that is at least 2 ppm.

If you have a healthy specimen, it will generally acclimate quickly. Hippopus Clams can do well under a variety of lighting intensities and occasional stronger currents will be tolerated. They are intolerant of changing salinity, they need sediment-free water, and you really don't want your water parameters to fluctuate too much. Keep a watch for predators. It is important to make sure they are not being irritated, not being fed upon by other organisms. For more in depth information on caring for HIppopus Clams see, Caring For Tridacnid Clams.

  • Water Changes: Bi-weekly - To keep water stable, test weekly.
  • Calcium Levels: 400.0 - 450.0 ppm - If using Seachem's calcium, 385 should suffice.
  • Alkalinity Levels: 8.0 - 12.0 dKH - Best at 9 dKH.
  • Magnesium Levels: 1,250.0 - 1,350.0 ppm - Adjust magnesium levels before checking calcium levels.
  • Strontium Levels: 5.0 - 15.0 ppm
  • Iodine Levels: - Add iodine daily as directed. Do not add full week's dose at once (may add to top off water).

Aquarium Setup

Hippopus Clams can be kept in a reef environment with live rock. Place them on the substrate in the bottom of the tank. Keep fluctuations in water parameters to a minimum and water flow low to moderate. These clams will grow very rapidly when provided adequate light and calcium levels. A high pH and high temperatures can cause problems.

The size of the tank should be at least 100 gallons per 12 to 18" of clam (though larger is better) as this will help keep water parameters stable. Live rock is necessary and sand is preferred if they will be on the substrate. A mature tank is also important. The tank should be at least 6 months old from the time of adding that last piece of live rock. Once you see Coralline algae growing (that cool pink and purple hard algae) you know your tank is doing well and ready for your clam. Where ever they are placed, make sure the eventual 4 feet of room they will occupy is free of shadowing.

Some care should be taken with placement of a new clam. Place it in the upper third of your tank tank unless it is a pale brown color. An H. hippopus showing pale brown color may have been damaged by insufficient lighting. However, be very careful not to expose it suddenly to intense light. Where ever it is placed, make sure the eventual 14 to 16" of room they will occupy is free of shadowing. Avoid placing these brown colored hippopus directly under strong metal halides.

These clams accept lower-light levels, not needing the strong light intensities of the Maxima Clam T. maxima or the Crocea Clam T. crocea. In the aquarium, however, Hippopus Clams will do well under moderate to relatively high lighting intensities. Provide moderate to strong lighting, such as reef fluorescent lights, intense LED, or T5 lighting if you are positioning them higher in the tank, or if your tank is shallower. Kelvin's that they do best at are 6K to 10K. Take great care if attempting to acclimate them to intense lighting such as metal halides. Hippopus Clams can be adapted to metal halide lighting, but this should be done over time as a gradual process.

Since salinity is critical, aim for 1.024 to prevent swinging out of the 1.023 and 1.025 range. Automatic fresh water top offs are highly suggested to keep salinity stable. Low to moderate flow is best, and turbulent as opposed to laminar. Choose an area of the tank where the water is a "dead spot" and that will please them.

Keep pH at 8.1 to 8.3, do not let the aquarium exceed a pH above 8.4. For hardness, maintain a dKH of 7.9-12, with the optimal being 9. A temperature between 74 to 86°F (23 to 30°C) is fine, however keeping it closer to 83°F is suggested, and be sure to keep it stable. For more in depth information on caring for Giant Clams see, Caring For Tridacnid Clams.

  • Minimum Tank Size: 100 gal (379 L) - Tank should be at least 6 months old, preferably with coralline algae growth.
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Amount
  • Substrate Type: Sand
  • Lighting Needs: Moderate - normal lighting - Kelvins: 6K to 10K to mimic the light levels they receive in the shallow habitats of their natural environment.
  • Temperature: 74.0 to 83.0° F (23.3 to 28.3° C) - Keep the temperature stable.
  • Specific gravity: 1.023-1.025 SG - Salinity is important, too high or low a salinity can cause the death of a clam. Stay within this range, aiming for 1.024.
  • Water Movement: Moderate - For the Hippopus Clam, low to moderate currents will be tolerated, but should not be a constant condition. Weak linear flow is okay, but moderate and turbulent is best.
  • Water Region: All - Dependent on lighting.

Social Behaviors

Clams are very stationary and peaceful, they are not aggressive towards other aquarium inhabitants. As the Hippopus Clam grows, it will lose its byssus gland. Though the byssus gland is what several Tridacna clams rely on to anchor themselves in place, that is not the case with these very large giant clams. The Hippopus Clam, just like the Gigas Clam T. gigas and the Derasa Clam T. derasa, grows so large and heavy it simply stays where is is put.

Although their shells can close tightly in mature specimens, they do need protection from anemones and some corals. They should not be kept near any stinging cell creatures and must be kept away from any sweeper tentacles. Anemones need to be watched, as they can move close to a clam and sting or eat it.

Hippopus Clams commonly have small creatures that live in the nooks and crannies of their shell. They are considered commensal, and they will not harm a healthy clam. Be cautious with tank inhabitants that may pick at the clam or eat its mantle, such as Trigger Fish and Puffers, Blennies, Butterfly Fish, and Clown Gobies. Angelfish and some shrimp may also disturb your clam.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species - conspecifics: Yes
    • Anemones: Monitor - Protect the clam from anemones that wander.
    • Mushroom Anemones - Corallimorphs: Monitor - Safe as long as they do not come in contact with the clam.
    • Leather Corals: Monitor - Should be okay if spaced apart.
    • Zoanthids - Button Polyps, Sea Mats: Monitor - Should be okay if spaced apart.
    • Sponges, Tunicates: Safe
    • Shrimps, Crabs, Snails: - Small commensal shrimp are fine if the clam is healthy. Remove any small, rice-sized snails found on the clam's surface with a toothbrush.
    • Starfish: Monitor - Starfish usually only eat dying organisms.
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: Safe
    • Crabs: Monitor - Tiny commensal crabs are okay on a healthy clam, avoid other crabs.
    • Snails: Safe - Make sure nassarius snails cannot turn a young clam over. Remove parasitic pyramidellid snails, other snails are safe.
    • Sea Apples, Cucumbers: Threat - The clam will die if these species expel their toxins. Giant clams are much more sensitive to these toxins than other invertebrates, even if the system is large.
    • Urchins, Sand Dollars: Monitor - Should be safe, but it is unknown if any or all species are safe.
    • Nudibranch, Sea Slugs: Monitor - Should be safe, but it is unknown if any or all species are safe.
    • Copepods, Amphipods, Mini Brittle Stars: Safe
    • Stony Corals: May be aggressive - Only safe as long as they do not come in contact. Stony corals can sting your clam.
    • Soft Corals: May be aggressive - Give clam plenty of space.

Sex: Sexual differences

There are no discernible sexual differences.

Breeding / Reproduction

Hippopus Clams are protandry, meaning they are born male and change to female. Like other giant clams, spawning is seasonal. Clams will release eggs and sperm that can number into the tens of thousands of eggs. This event tends to happen around sunset. One aquarist noted a spawning clam pulsing out eggs every two minutes. Once the eggs are externally fertilized, the embryos develop into trocophore larva, which are free-swimming. The next stage is the bivalve veliger, which sort of looks like a tiny free swimming clam. Once they are 4 to 20 mm long, they will start to burrow into the reef and begin their lives in their new home.

The Hippopus Clam has been propagated in captivity and is a relatively easy clam to breed in aquaculture systems. The coloring of aquacultured specimens are becoming more and more attractive, and many have a strong lime-green striping. The demand from aquarists has raised interest in producing colorful varieties of all the giant clam species. For detailed information on clam propagation, see Giant Clam Breeding and Reproduction

  • Ease of Breeding: Moderate

Ailments / Diseases

Keep a watch out for predators! The most dangerous predators are the highly prolific pyramidellid snails of the Tathrella, Pyrgiscus, and Turbonilla genera. These are parasitic snails about the size of a grain of rice or smaller, rarely reaching a maximum size of about 7mm in length. These snails attack giant clams with a trunk-like snout called a "proboscis." They punch holes into the clam's soft tissue and then feed on its bodily fluids.

While in nature, giant clams can deal with a few of these parasitic snails, in captivity these snails tend to multiply to dangerous numbers. They may hide in the scutes of the clam or in the substrate by day, but will often will be found around the edges of the clam's mantle tissue or byssal gape (large foot hole) after the lights go out. They can produce numerous small, gelatinous, egg masses on the clam's shell. These masses are transparent, so difficult to spot. Before putting it in the tank, scrub your clam's shell vigorously with a toothbrush, or other brush with firm bristles, to remove the snails and their eggs. Be careful not to scrub the clam's soft tissues, as that can cause injury and lead to infection. Inspect your clam regularly for several months and remove any snails you discover.

Some other common ailments of Giant Clams:

  • Pinched Mantle: Another common affliction of giant clams is called the Pinched Mantle disease. The edges of the mantle become pinched and contorted, and the margins won't extend fully. This condition almost always results in death unless treated, and it can spread to other clams. The actual cause of this ailment is unknown, but it may possibly be an attack by some sort of protozoan. An easy treatment, that is is stressful but effective, is to submerse the clam in a freshwater dip for a few minutes. Signs of recovery can take a day or two.
  • Bubble Mantle: Caused by laminar flow directed at the clam or pouring water directly into the aquarium in a way that causes bubbles to form (use a siphon and water pump and/or pour very slowly and carefully or pour into sump only). These bubbles can get stuck in the clam's mantle with can cause illness and death.
  • Gaping: The larger of the two holes is gaping open, larger than normal. This is usually due to poor water quality. Stability of your water parameters need to be checked quickly and addressed.

Giant clams are also quite sensitive to chemicals or toxic substances dissolved in the water, so be sure to maintain good water quality. As mentioned under aquarium care and aquarium parameters above, high pH, high salinity, and high temperatures can also cause problems. Avoid large weekly doses of anything, especially iodine, which has been known to kill them. For in-depth information on potential Tridacna clam problems, see: Tridacnid Clams: Friends, Enemies & Ailments.


Hippopus Clams are seasonal spawners, but those btained from aquaculture systems are readily available online, and it may be possible to special order them in stores. They range in size, usually from 2" to 5.5" in size, and are moderate to somewhat expensive. .

Though once rare in the aquarium trade, and seldom found in fish stores or hobbyist tanks, today the Hippopus Clams obtained from aquaculture systems are becoming more readily available and are very hardy in reef aquariums. According to the The Reef Aquarium Volume One by J. Charles Delbeek and Julian Sprung, the H. hippopus offered for sale to hobbyists in North America are the products of aquaculture programs. None are wild caught.


Author: Clarice Brough CFS, Elizabeth M. Lukan, Carrie McBirney
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