Hippopus Clam ~ H. hippopus

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

Family: CardiidaeHippopus Clam - H. hippopus also known as Bear Paw Clam, Horse's Hoof Clam, Strawberry Clam, and China ClamHippopus hippopusPhoto © Gerald Heslinga, Indo-Pacific Sea Farms

   The Hippopus Clam (known as the Bear Paw Clam) is not only a hardy aquarium specimen, but is prized for its very colorful and decorative shell!

   There are two species of giant clams that are 'Hippopus Clams'. The species commonly referred to as the Hippopus Clam H. hippopus, is also known as the Bear Paw Clam, Horse's Hoof Clam, and the Strawberry Clam. H. hippopus is a hardy giant clam that is easy to acclimate and keep in the home aquarium, as long as it is given enough space to grow. Its close relative, the China Clam H. porcellanus, is not common in the aquarium industry. However both of these giant clams are traditionally harvested for their meat, and they are also highly prized for their shells.

   The decorative shell of H. hippopus is thick, heavily ribbed, and decorated with rows of round strawberry red markings. Thus the name Strawberry Clam. The China Clam H. porcellanus has a thinner shell that is less deeply ribbed and lacks much of the strawberry coloring, Being quite large, the shells of either Hippopus Clam can be cleaned, bleached and polished for a number of uses. Common uses for giant clam shells are as ornaments, night lights, and soap dishes, but a favorite use for the large decorative Hippopus Clams is as serving bowls.

   Besides being called the Strawberry Clam, derived from its red colored markings, the H. hippopus has a couple other descriptive common names. The two 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 valves is shaped like a horse's foot.


Geographic Distribution
Hippopus hippopus
Data provided by GBIF.org
  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Bivalvia
  • Order: Veneroida
  • Family: Cardiidae
  • Genus: Hippopus
  • Species: hippopus
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Scientific name

  Hippopus hippopus

Distribution / Background

   The Hippopus Clam, also known as Bear Paw Clam, Horse's Hoof Clam, and the Strawberry Clam, is found in the Indo-Pacific region and is hunted for food and souvenirs. Hippopus hippopus was first described by Linnaeus in 1758.
   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, it is usually found lose on sandy bottoms or near-reef flats. It can be found in the shallows and as deep as 19.7 feet (6 meters). The clam doesn't burrow so the shell is exposed and is usually found with various organisms hitching rides.

Status

   The Hippopus hippopus is currently not listed on the IUCN Red List, however its close relative the China Clam Hippopus porcellanus is listed as LR/cd - Lower Risk: conservation dependent Species.

Description

Hippopus hippopus by Gerald Heslings of IPSF   The Hippopus Clam Hippopus hippopus can grow to a maximum length of 18 inches (45cm).

   Some characteristics of the H. hippopus clam:

  • The mantle is dull green/brown to gray with some faint gold stripes.
  • The mantle doesn't extend past the edge of the shell.
  • Shells are thick and very heavy.
  • 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 Hippopus Clam grows it loses its byssal gland and relies solely on its size and weight to hold its place.

   Comparing Hippopus Clams to other species of Giant Clams:

   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.

Difficulty of Care

   The Hippopus Clam not only grows into a large, heavy, and distinctively beautiful clam, but can be a good choice for a beginning saltwater enthusiast. This giant clam is very easy to keep in the home aquarium if provided with enough room for growth. It is a hardy clam that can easily acclimated to your tank.

Foods / Feeding

   It is generally believed that giant clams do not require feeding in the aquarium. Most clams fulfill their nutritional requirements by filter feeding and absorbing dissolved organic compounds from the water. The Tridacninae family of clams have gone even further than this, using zooxanthellae to manufacture food for themselves.
   The Hippopus clams receive the majority of their nutrition from their zooxanthellae. Whether additional feeding is required is still debated. Some enthusiasts believe they should be fed, going on the assumption that they are filter feeders like other clams. If you wish to feed your clam, it is suggested that they be fed micro-foods designed for filter feeders, especially when small. A yeast-based suspension is one suggestion, unless the tank has other fish and corals that are regularly being fed, or you can offer other micro-foods such as phytoplankton or commercially prepared micro-foods like 'marine snow' or 'reef snow'.
  Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and possibly a minute amount of nitrate.

  • 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. 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 in giant clams.
  • Nitrate: They require some nitrogen for proper growth. Nitrate can be added if levels are extremely low, but be careful as nitrates should never exceed 2 mg/L.

   For more information about the feeding process of Giant Clams see What Do Clams Eat.

Aquarium Care

   If a healthy clam is obtained, these clams are hardy in captivity and relatively easy to keep. With proper lighting, good filtration, and careful attention the Hippopus Clams require require little else in the way of care. It is important to make sure they are not being irritated, not being fed upon by other organisms, and good water quality must be maintained.

  • If you have a healthy specimen, it will generally acclimate quickly.
  • Keep a watch for predators as this clam can be easy prey with its large and wide byssus gland opening.
  • 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!

Aquarium Parameters

   Hippopus Clams can be kept in a reef environment with live rock. Keep fluctuations in water parameters to a minimum and water flow low to moderate. A high pH and high temperatures can cause problems.

  • Lighting: They accept lower-light levels, not needing the strong light intensities of the Maxima Clam T. maxima or the Crocea Clam T. crocea. However 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. Be very careful not to expose it suddenly to intense light.
       An H. hippopus showing pale brown color may have been damaged by insufficient lighting. Avoid placing these brown colored hippopus directly under strong metal halides.
  • Temperature: Mid to Upper 70° F. (mid 20° C.). Do not let the aquarium exceed 84° F.
  • Salinity / Specific Gravity: 1.024. Salinity is also important, too high or low a salinity can cause the death of a clam. Try to keep specific gravity between 1.023 and 1.025.
  • pH: 8.3. Do not let the aquarium exceed a pH above 8.4.
  • Hardness: Maintain a dkh of 7.9.
  • Water Movement: For the Hippopus Clam, low to moderate currents will be tolerated.

   For more in depth information on caring for Hippopus Clams see, Caring For Tridacnid Clams

Compatibility and Social Behaviors:

   Clams are very stationary and peaceful, they are not aggressive towards other aquarium inhabitants. As the Giant 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 the 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.
   Be cautious with other tank inhabitants as well, those that may pick at the clam or eat its mantle, such as Trigger Fish and Puffers. Blennies, Butterfly Fish, Clown Gobies, Angelfish and shrimp may disturb Tridacna clams.

Breeding and Reproduction

   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 of giant clam and tridacnid propagation, see Giant Clam Breeding and Reproduction

Potential Problems

   Keep a watch out for predators! The Hippopus Clam can be easy prey with its large and wide byssus gland opening. They 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.

   For in depth information on potential Giant clam problems, see: Tridacnid Clams: Friends, Enemies & Ailments

Availability

   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.

Authors: Elizabeth M. Lukan / Clarice Brough, CFS.

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