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    1. Species/
    2. Molluscs/
    3. Tridacna crocea

    Molluscs · Cardiidae

    Tridacna crocea

    Crocus clam

    The smallest giant clam, 15 cm at most, and the most colourful: its blue, green, purple, gold or brown mantle covers a thick shell. In the wild it lives embedded in coral heads, where it bores its own pocket.

    • intermediate level
    • Reef Safe
    • CITES Appendix II
    Light
    High
    Water flow
    Medium
    Adult size
    ≤ 15 cm

    This sheet is still being written. Some sections are not filled in yet: they stay hidden while they are empty.

    On this sheet

    1. Water parameters
    2. Care and feeding
    3. Compatibility
    4. Description
    5. Conservation
    6. Classification
    7. Sources

    What it needs

    Water parameters

    • Temperature°C
      2230
      22.2–25.6 °C
    • SalinitySG
      1.021.03
      1.023–1.025 SG

    Related species

    Other molluscs

    See all molluscs →
    M

    Smooth giant clam

    Tridacna derasa

    M

  1. pH
    7.68.6
    8.1–8.4
  2. Alkalinity (KH)dKH
    513
    8–11 dKH
  3. Calciumppm
    350500
    380–450 ppm
  4. Magnesiumppm
    1,1501,500
    1,280–1,350 ppm
  5. Range recommended by the sheet

    Day to day

    Care and feeding

    • LevelIntermediate
    • FoodFilter Feeder

    Care

    Acclimation: invertebrates cope badly with even small changes in water chemistry, and clams are sensitive to salinity changes. Acclimate it slowly, by floating and then drip, and never rush the process. It must then get used to the light: a clam under 5 cm has a thinner mantle and is more sensitive to very intense lighting. Start it on the bottom, on a small rock or in a dish of coarse substrate, then move it up gradually, as you would a newly added coral.

    Setup: it needs intense lighting and moderate water flow. Place it in the rockwork, on a hard surface where it can attach its byssus and, over time, bore into porous rock; it attaches within a few days, so treat its first spot as permanent. Never pull it off once it has attached: the foot and tissues would be fatally damaged. As a last resort, cut the byssal threads one by one with a razor blade, close to the surface, without touching the tissue.

    Tankmates: it is a peaceful animal that harms nothing, but in an aquarium anemones, triggerfish and puffers may attack it, and a wandering anemone may sting it. Inspect it before adding it, and quarantine it if you can, to spot parasitic Pyramidellidae snails: they are white, conical, a few millimetres long, and feed on the clam on its shell and foot until it weakens or dies. Remove them by hand (a toothpick will do), checking day after day; the wrasses Halichoeres melanurus and Halichoeres chrysus eat them.

    Health signs and sensitivities: the mantle edge carries hundreds of simple eyes; the clam partly closes when the light dims, a shadow passes or an object moves, which is a normal reflex. A mantle that no longer opens fully for several days, on the other hand, should make you look for parasites. Like all invertebrates, it does not tolerate copper treatments. It builds its shell from calcium carbonate, so it draws on the tank's calcium and alkalinity.

    Water: aim for 22 to 25.5 °C, a specific gravity of 1.023 to 1.025, pH 8.1 to 8.4, 380 to 450 mg/L calcium, 1280 to 1350 mg/L magnesium and an alkalinity of 8 to 11 dKH.

    Feeding

    A clam lives mainly on its zooxanthellae, microscopic algae housed in its mantle: in the giant clam they cover 65 to 70% of its needs. It also filters the water continuously and absorbs dissolved matter through its skin.

    Small clams rely more on filtering: in a very small clam it provides about 65% of the carbon, against 34% in a larger one. Above 5 cm no feeding is needed; below that, give phytoplankton several times a week if your tank is low in nutrients.

    Decor

    • Hard, porous rock to attach its byssus and bore into
    • A brightly lit spot, reached gradually
    • A permanent spot from day one: it attaches within days

    Tank mates

    Compatibility

    Goes well with

    • ✓Halichoeres melanurus and Halichoeres chrysus: these wrasses eat parasitic Pyramidellidae snails
    • ✓Corals and peaceful fish of a brightly lit reef tank: the clam harms no other organism

    Avoid

    • ✕Anemones: they may move next to the clam, sting it or eat it
    • ✕Triggerfish and puffers: possible predators in the aquarium
    • ✕Copper-based treatments

    In detail

    Description

    Identification: thick, heavy, greyish-white shell, sometimes edged with orange or yellow, much taller than that of T. maxima, with low ribs often worn by boring; the byssal opening under the shell is very wide. The mantle is so variable that it is no identification criterion: T. maxima is the closest look-alike.

    In the wild: from the Andaman Islands to Fiji, Japan to New Caledonia and Queensland, 0 to 20 m. It attaches with its byssus and then sinks into the limestone by opening and closing its shell, hence the name "boring clam"; this pocket protects it from sea stars, angelfish and butterflyfish that eat bivalves. It may now be locally extinct in Guam and the Mariana Islands.

    Reproduction: gametes are released into open water; the larva swims freely before settling. Clams sold in the hobby are raised on farms in the Central and South Pacific.

    Status: Least Concern on the IUCN Red List (2024 assessment), but, like all giant clams, listed in CITES Appendix II since 1985 and in Annex B of the EU regulation: any international trade requires a permit.

    Characteristics

    • 15 cm at most: the smallest giant clam.
    • Very colourful, variable mantle (blue, green, purple, gold, brown): colour does not help identify it.
    • Bores into limestone with its shell and lives embedded in coral.
    • Very wide byssal opening under a thick, tall shell.
    • Lives on its zooxanthellae and filters the water.
    • Traded specimens are raised on Pacific farms.
    • CITES Appendix II, EU Annex B.

    Origin

    • Indo-West Pacific

    Distribution

    • From the Andaman Islands to Fiji, Japan to New Caledonia and Queensland
    • Possibly locally extinct in Guam and the Mariana Islands
    • 0 to 20 m deep

    Status

    Conservation

    IUCN Red List
    LCNTVUENCREWEX

    Least concern (LC)

    See on iucnredlist.org (opens in a new tab)

    CITES

    CITES Appendix II

    EU Annex B

    checked on November 11, 2026 · Source: Species+ (opens in a new tab)

    WoRMS

    Classification

    Kingdom
    Animalia
    └
    Phylum
    Mollusca
    └
    Class
    Bivalvia
    └
    Order
    Cardiida
    └
    Family
    Cardiidae
    └
    Genus
    Tridacna
    └
    Species
    Tridacna crocea

    AphiaID 207673 · See on WoRMS (opens in a new tab)

    Where this comes from

    Sources

    1. [1]WoRMSWoRMS — Tridacna crocea Lamarck, 1819 (AphiaID 207673) (opens in a new tab) · accessed on November 11, 2026
    2. [2]IUCNIUCN Red List — Tridacna crocea: LC (assessed 10 June 2024) (opens in a new tab) · accessed on November 11, 2026
    3. [3]CITESSpecies+ — Tridacna crocea (CITES Appendix II, EU Annex B; listed with Tridacnidae spp. since 1985) (opens in a new tab) · accessed on November 11, 2026
    4. [4]WebSeaLifeBase — Tridacna crocea (species summary: size, depth, distribution, biology) (opens in a new tab) · accessed on November 11, 2026
    5. [5]WebWikipedia (en) — Tridacna crocea (opens in a new tab) · accessed on November 11, 2026
    6. [6]WebWikipédia (fr) — Tridacna crocea (bénitier crocus) (opens in a new tab) · accessed on November 11, 2026
    7. [7]WebLiveAquaria — Crocea Clam, Multicolored, Aquacultured (quick stats and overview) (opens in a new tab) · accessed on November 11, 2026
    8. [8]WebLiveAquaria — Acclimation Guides (why acclimate; floating and drip methods) (opens in a new tab) · accessed on November 11, 2026
    9. [9]WebQuality Marine — Hippopus Clam, Hippopus hippopus (description, care info, water conditions) (opens in a new tab) · accessed on November 11, 2026
    10. [10]WebReefs.com (DaniReef, L. Gallizio) — Pyramidellidae snails: Tridacna killers, how to eradicate them (2017) (opens in a new tab) · accessed on November 11, 2026
    11. [11]WebWikipedia (en) — Giant clam, Tridacna gigas (eyespots, feeding share of zooxanthellae, larval development, aquaculture history, myths) (opens in a new tab) · accessed on November 11, 2026
    12. [12]WebWikipedia (en) — Tridacna squamosa (in captivity: predators, anemones, Pyramidellidae, nitrate uptake) (opens in a new tab) · accessed on November 11, 2026
    13. [13]WebWikipedia (en) — Tridacninae (subfamily of Cardiidae; CITES Appendix II; farming) (opens in a new tab) · accessed on November 11, 2026
    UpdatedNov 11, 2026
    Versionv2
    Report an error on this sheet
    Giant clam

    Tridacna gigas

    M

    Maxima clam

    Tridacna maxima

    M

    Tevoro clam

    Tridacna mbalavuana

    M

    Noah's giant clam

    Tridacna noae

    M

    Fluted giant clam

    Tridacna squamosa

    M

    Tridacna squamosina

    M

    Smooth giant clam

    Tridacna derasa

    M

    Giant clam

    Tridacna gigas

    M

    Maxima clam

    Tridacna maxima

    M

    Tevoro clam

    Tridacna mbalavuana

    M

    Noah's giant clam

    Tridacna noae

    M

    Fluted giant clam

    Tridacna squamosa

    M

    Tridacna squamosina

    M

    Horse's hoof clam

    Hippopus hippopus

    M

    Smooth giant clam

    Tridacna derasa

    M

    Giant clam

    Tridacna gigas

    M

    Maxima clam

    Tridacna maxima

    M

    Tevoro clam

    Tridacna mbalavuana

    M

    Noah's giant clam

    Tridacna noae

    M

    Fluted giant clam

    Tridacna squamosa

    M

    Tridacna squamosina

    M

    Horse's hoof clam

    Hippopus hippopus