Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Pinctada imbricata radiata
(rayed pearl oyster)



Pinctada imbricata radiata (rayed pearl oyster)


  • Last modified
  • 25 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Pinctada imbricata radiata
  • Preferred Common Name
  • rayed pearl oyster
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Mollusca
  •       Class: Bivalvia
  •         Subclass: Pteriomorphia

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External view of Pinctada radiata shell.
TitleExternal view
CaptionExternal view of Pinctada radiata shell.
CopyrightStratos Xentidis
External view of Pinctada radiata shell.
External viewExternal view of Pinctada radiata shell.Stratos Xentidis
Internal view of Pinctada radiata shell.
TitleInternal view
CaptionInternal view of Pinctada radiata shell.
CopyrightStratos Xentidis
Internal view of Pinctada radiata shell.
Internal viewInternal view of Pinctada radiata shell.Stratos Xentidis


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Preferred Scientific Name

  • Pinctada imbricata radiata (Leach, 1814)

Preferred Common Name

  • rayed pearl oyster

Other Scientific Names

  • Avicula albina var. vaillanti Vassel, 1897
  • Avicula chemnitzii Philippi, 1849
  • Avicula occa Reeve, 1857
  • Avicula radiata Leach, 1814
  • Avicula radiata var. canarina Philippi, 1849
  • Margaritifera vulgaris Schumacher
  • Meleagrina conemenosi Monterosato, 1884
  • Meleagrina occa Reeve, 1857 [Pallary, 1912; Issel, 1869]
  • Meleagrina radiata (Deshayes) [Tiller and Bavay, 1905]
  • Meleagrina savignyi Monterosato, 1884
  • Meleagrina vulgaris (Schumacher, 1817)
  • Pinctada aerata (Reeve, 1857)
  • Pinctada badia (Dunker, 1852)
  • Pinctada fimbriata (Dunker, 1872)
  • Pinctada fuctata (Gould, 1850)
  • Pinctada imbricata (Röding, 1798; Reeve, 1857; Jameson, 1901)
  • Pinctada lacunata (Reeve, 1857)
  • Pinctada longisquamosa (Dunker, 1872)
  • Pinctada martensii (Dunker, 1872)
  • Pinctada nebulosa (Conrad, 1837)
  • Pinctada pernoides (Reeve, 1857)
  • Pinctada perviridis (Reeve, 1857)
  • Pinctada radiata (Leach, 1814)
  • Pinctada squamulosa (Lamarck, 1819)
  • Pinctada varia (Dunker, 1872)
  • Pinctada vulgaris (Schumacher) [Tomlin, 1927]

International Common Names

  • English: Ceylon pearl oyster; Persian Gulf pearl oyster
  • Spanish: pintadina radiada
  • French: pintadine radiée
  • Arabic: balbal; mohar

Local Common Names

  • : Atlantic pearl oyster; Venezuela lingah
  • Australia: Australian lingah; bastard shell
  • Indian Ocean, Western: bil-bil
  • Japan: Akoya pearl oyster
  • Myanmar: pate goung
  • USA/Hawaii: pipi; unahi pipi

Summary of Invasiveness

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According to Streftaris and Zenetos (2006), P. imbricata radiata is considered to be one of the worst invasive species in the Mediterranean Sea, in terms of spread and impact. It is a relatively hardy species, tolerant to emersion (O’Connor et al., 2003) and to a wide temperature range (13-30°C) (DAISIE, 2009). It also has the ability to adapt to a changed environment (Mohamed et al., 2006) and its tolerance to chemical contamination has enhanced its expansion in enclosed polluted ecosystems (Katsanevakis et al., 2008). It is considered to be a habitat-modifying and gregarious bivalve, capable of impacting native fauna by forming oyster banks (DAISIE, 2009).

It was first recorded as invasive in Tunisia (Vassel, 1896). It is now established in all places where it has been introduced and it is steadily expanding its range (DAISIE, 2009). P. imbricata radiata is currently not on any alert list, but it is listed among the worst alien species in the Streamlining European 2010 Biodiversity Indicators on invasive alien species (European Environment Agency, 2007).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Mollusca
  •             Class: Bivalvia
  •                 Subclass: Pteriomorphia
  •                     Order: Pterioida
  •                         Unknown: Pterioidea
  •                             Family: Pteriidae
  •                                 Genus: Pinctada
  •                                     Species: Pinctada imbricata radiata

Notes on Taxonomy and Nomenclature

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There is much confusion about the taxonomy and little agreement among authors about the correct scientific name of this important economic species. Over the years, this species has been described with over 20 names by different authors (i.e. Roding, 1748; Schumacher, 1817; Lamarck, 1819; Conrad, 1837; Phillippi, 1849, Gould, 1850; Reeve, 1857; Dunker, 1872; Monterosanto, 1884; Vassel, 1897). This large number of synonyms is due to the wide variety in shape, strength of sculpture, and colour of P. imbricata radiata shells (Zenetos et al., 2004a). 

In recent times, depending on the area, it has been generally known as Pinctada imbricata (Central America and Australia), Pinctada radiata (Persian Gulf, Red Sea, Mediterranean Sea), Pinctada vulgaris (Sri Lanka), and Pinctada fucata (Japan, India, Eastern Pacific ocean). Ranson (1961) put Pinctada fucata and other species in the synonymy of P. imbricata radiata with P. radiata limited to the Arabian Gulf and Red Sea, while Shirai (1994) places those species including P. radiata in synonymy with Pinctada imbricata. Carpenter and Niem (1998) suggested that Pinctada radiata (Leach, 1814) must be used as the oldest available name.
The matter is not fully resolved as molecular results are contradictory. The papers by Tëmkin (2010) and Cunha et al. (2011) were published at similar times and do not discuss each other's results. Tëmkin treated fucata and radiata as geographical subspecies of imbricata, whereas Cunha et al. presented a molecular tree that resolved them at the rank of species. This may be a result of the two papers using different markers: Tëmkin used 18S, 28S, 16S, and H3, whereas Cunha et al. used 18S and CO1 (Bouchet, 2016). Here, we follow the latest nomenclature used in WoRMS.


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Adult P. imbricata radiata have a fragile, rather thin and compressed, small to medium size shell. The shell is inequivalve with the left valve more inflated, and has an almost quadrate outline. The dorsal margin is relatively long, and definitely longer than the body of the shell. The posterior margin is slightly concave and protrudes only slightly (or not at all) beyond the tip of the anterior ear. The beaks point anteriorly, and the hinge line is straight with no teeth present. The ligament is set in a single triangular depression. The common size of this oyster is usually 50-65 mm.

The external coloration of the shell is variable. It can be uniform or with darker markings on radial rays, and is generally brownish or reddish. Sometimes, green and bronze coloration has been observed. The outer surface has densely set, appressed and flattened imbricating concentric lamellae, and often moderately small radially projecting spines, mostly preserved towards the margins. The internal side has a highly iridescent nacreous area, whereas the non-nacreous margin is glossy and light brown in colour, usually with dark brown or reddish blotches corresponding to the main external rays (Zenetos et al., 2004a).


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P. imbricata radiata is a bivalve with a very wide distribution. It is found in both hemispheres and in most oceans and seas around the world. It is present in the Atlantic, Pacific and Indian oceans, the Persian Gulf, the Red Sea, and more recently in the Mediterranean Sea.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Sea Areas

Atlantic, NortheastLocalisedIntroduced1998Àvila et al., 1998Azores Islands
Atlantic, SouthwestPresentNative Not invasive Leal, 2002
Atlantic, Western CentralPresentNative Not invasive Leal, 2002
Indian Ocean, EasternWidespreadNative Not invasive Poutiers, 1998a
Indian Ocean, WesternWidespreadNative Not invasive Poutiers, 1998a
Mediterranean and Black SeaWidespreadIntroduced1874 Invasive Monterosato, 1878
Pacific, Eastern CentralPresentNative Not invasive Poutiers, 1998a
Pacific, NorthwestWidespreadNative Not invasive Poutiers, 1998a
Pacific, SouthwestPresentNative Not invasive Poutiers, 1998a
Pacific, Western CentralPresentNative Not invasive Poutiers, 1998a


BahrainPresentNative Not invasive CIBJO, 2006
Brunei DarussalamPresentNative Not invasive Poutiers, 1998a
CambodiaPresentNative Not invasive Poutiers, 1998a
ChinaPresentNative Not invasive Hwang et al., 2007
East TimorPresentNative Not invasive Poutiers, 1998a
IndiaPresentNative Not invasive Poutiers, 1998a
IndonesiaPresentNative Not invasive Poutiers, 1998a
IranPresentNative Not invasive Doroudi, 1996
IsraelPresentIntroduced1899 Invasive Barash and Danin, 1973; Edelman-Furstenberg, 2008
JapanPresentNative Not invasive Poutiers, 1998a
KuwaitPresentNative Not invasive CIBJO, 2006
LebanonWidespreadIntroduced1965 Invasive Zibrowius and Bitar, 1981; Crocetta et al., 2013
MalaysiaPresentNative Not invasive Poutiers, 1998a
MyanmarPresentNative Not invasive Poutiers, 1998a
OmanPresentNative Not invasive Al-Khayat and Al-Ansi, 2008
PhilippinesPresentNative Not invasive Poutiers, 1998a
QatarWidespreadNative Not invasive Al-Madfa et al., 1998
Saudi ArabiaPresentNative Not invasive Gladstone, 2002
SingaporePresentNativePoutiers, 1998a
Sri LankaPresentNativePoutiers, 1998b
SyriaPresentIntroduced1975 Invasive Kinzelbach, 1985
TaiwanPresentNative Not invasive Poutiers, 1998a
ThailandPresentNative Not invasive Poutiers, 1998a
TurkeyLocalisedIntroduced1982 Invasive Kinzelbach, 1985; Mutlu, 2013
United Arab EmiratesPresentNative Not invasive Al-Khayat and Al-Ansi, 2008
VietnamPresentNative Not invasive Poutiers, 1998a


EgyptPresentIntroduced1874 Invasive Monterosato, 1878Native on Red Sea coast, Introduction in Mediterranean coast
LibyaPresentIntroduced1913 Invasive Monterosato TAdi, 1917; Abushaala et al., 2014
MadagascarPresentNative Not invasive Poutiers, 1998a
TunisiaPresentIntroduced1890 Invasive Vassel, 1896; Lakhrach et al., 2012

North America

BermudaPresentNative Not invasive Leal, 2002
CanadaPresentNative Not invasive Leal, 2002
MexicoPresentNative Not invasive Leal, 2002
USAPresentNative Not invasive Turgeon et al., 1998
-HawaiiPresentNative Not invasive Poutiers, 1998a

Central America and Caribbean

Antigua and BarbudaPresentNative Not invasive Leal, 2002
BahamasPresentNative Not invasive Leal, 2002
BarbadosPresentNative Not invasive Leal, 2002
BelizePresentNative Not invasive Leal, 2002
Costa RicaPresentNative Not invasive Leal, 2002
CubaPresentNative Not invasive Leal, 2002
CuraçaoPresentNative Not invasive Leal, 2002
DominicaPresentNative Not invasive Leal, 2002
Dominican RepublicPresentNative Not invasive Leal, 2002
GrenadaPresentNative Not invasive Leal, 2002
GuadeloupePresentNative Not invasive Leal, 2002
GuatemalaPresentNative Not invasive Leal, 2002
HaitiPresentNative Not invasive Leal, 2002
HondurasPresentNative Not invasive Leal, 2002
JamaicaPresentNative Not invasive Leal, 2002
MartiniquePresentNative Not invasive Leal, 2002
NicaraguaPresentNative Not invasive Leal, 2002
PanamaPresentNative Not invasive Leal, 2002
Puerto RicoPresentNative Not invasive Leal, 2002
Saint Kitts and NevisPresentNative Not invasive Leal, 2002
Saint LuciaPresentNative Not invasive Leal, 2002
Saint Vincent and the GrenadinesPresentNative Not invasive Leal, 2002
Trinidad and TobagoPresentNative Not invasive Leal, 2002
United States Virgin IslandsPresentNative Not invasive Leal, 2002

South America

BrazilPresentNative Not invasive Leal, 2002
ColombiaPresentNative Not invasive Leal, 2002
French GuianaPresentNative Not invasive Leal, 2002
GuyanaPresentNative Not invasive Leal, 2002
SurinamePresentNative Not invasive Leal, 2002
VenezuelaPresentNative Not invasive Leal, 2002


AlbaniaPresentIntroduced2010Katsanevakis et al., 2011
CroatiaPresentIntroduced2006Dogan and Nerlovic, 2008
CyprusPresentIntroduced1899 Invasive Monterosato, 1899
FrancePresentIntroduced1996Zibrowius, 1979; Boudouresque, 1999
GreeceWidespreadIntroduced1961 Invasive Serbetis, 1963
IrelandPresentIntroduced2013-2014Holmes et al., 2015on macro-litter; one shell
ItalyPresentIntroduced1917 Invasive Stasolla et al., 2014
MaltaLocalisedIntroduced1912 Invasive Pallary, 1912; Evans et al., 2015; Barbieri et al., 2016
PortugalPresentPresent based on regional distribution.
-AzoresPresentIntroduced1998Cardigos et al., 2006
UKPresentIntroduced1986Turk, 1988; Holmes et al., 2015shells only/on macro-litter


AustraliaPresentNative Not invasive Poutiers, 1998a
New CaledoniaPresentNative Not invasive Poutiers, 1998a
PalauPresentNative Not invasive Poutiers, 1998a
Papua New GuineaPresentNative Not invasive Poutiers, 1998a
Solomon IslandsPresentNative Not invasive Poutiers, 1998a
VanuatuPresentNative Not invasive Poutiers, 1998a

History of Introduction and Spread

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P. imbricata radiata was first reported outside its natural biogeographical distribution in 1874 in the Mediterranean Sea. It was collected on the shores of Alexandria, Egypt and was one of the very first marine species of Indo-Pacific origin to cross the Suez Canal into the Mediterranean. It was subsequently reported from Tunisia (1890), Israel (1899), Cyprus (1899), and Malta (1912).

In 1963 it was imported for aquaculture purposes to Greece, but its cultivation did not prove prosperous and was thus abandoned. However, P. imbricata radiata was naturalised and expanded in the Hellenic Seas (Pancucci-Papadopulou et al., 2005). Subsequent findings of this species in areas where aquaculture activities (historical or recent) are absent support a Lessepsian mode of introduction (Zenetos et al., 2005). Furthermore, molecular studies of P. imbricata radiata populations in the Saronikos area (Greece) have rather excluded shipping as the mode of transportation (Zenetos et al., 2004b).

In 1965 it was reported in Lebanon and in the early 1970s it was also reported in Libya (1973) and Syria (1975). In 1979, individuals of this species were found attached on the hull of a naval vessel in the port of Toulon, France (Zibrowius, 1979). It was reported in 1982 from Italy (Di Natale, 1982) and Turkey. More recently it was reported in the northern Adriatic Sea, in Croatia (2006). It is suspected that the populations in France and the northern Adriatic Sea are due to shipping transport (DAISIE, 2009). It is now well established in the eastern Mediterranean Sea and seems to be expanding (DAISIE, 2009). It is also reported to be established and spreading in the Central Mediterranean (Italy: Lodola et al., 2013; Stasolla et al., 2014. Malta: Evans et al., 2015).

In the Azores, (Northwestern Atlantic Ocean) P. imbricata radiata individuals were first found in 1998 attached to a ball-float near Faial. Later, there was a second report of occurrence in Vila Franca do Campo (São Miguel) (Àvila et al., 2000). The vector is still unknown but it is presumed that the introduction was not deliberate (Cardigos et al., 2006).

Winston et al. (1997) recorded Pinctada attached to marine litter off the coast of Florida. The species was also included in trans-Atlantic rafting mollusca on macro-litter: American molluscs on British and Irish shores (Holmes, 2015).


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Azores 1998 Cardigos et al. (2006)
Croatia 2006 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Dogan and Nerlovic (2008)
Cyprus 1899 Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Buzzurro and Greppi (1997)
Egypt 1874 Interbasin transfers (pathway cause) Yes Monterosato (1878)
France 1979 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Zibrowius (1979)
Greece 1963 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Serbetis (1963)
Ireland USA   Holmes et al. (2015) marine litter
Israel 1899 Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Barash and Danin (1973)
Italy 1982 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Natale ADi (1982) Sicily
Lebanon 1965 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Zibrowius and Bitar (1981)
Libya 1973 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Barash and Danin (1973)
Malta 1912 Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Pallary (1912)
Syria 1975 Aquaculture (pathway cause) ,
Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Kinzelbach (1985) Corsica
Tunisia 1890 Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Vassel (1896)
Turkey 1982 Breeding and propagation (pathway cause) ,
Interbasin transfers (pathway cause)
Yes Kinzelbach (1985)
UK USA   Holmes et al. (2015) marine litter

Risk of Introduction

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P. imbricata radiata is currently spreading towards the north and western Mediterranean Sea (DAISIE, 2009) and it is suspected that it will slowly expand throughout the Mediterranean coastline. The relatively recent record of its finding in the Azores (northeastern Atlantic Ocean) (Àvila et al., 1998), indicates that there is a strong possibility of this species spreading towards the European Atlantic coast as well.


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P. imbricata radiata individuals are byssally attached to rocks, dead corals and various submerged objects, often forming large natural banks. They are most common on sub-littoral bottoms from depths of 5 to 25 m, but they can also be found on the littoral and shelf zones from low tide levels to a depth of about 150 m. On soft bottoms, they aggregate to one another (Carpenter and Niem, 1998).

Habitat List

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Inland saline areas Principal habitat Natural
Estuaries Principal habitat Natural
Lagoons Principal habitat Natural
Inshore marine Principal habitat Natural
Benthic zone Principal habitat Natural

Biology and Ecology

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The biology of pearl oysters is poorly understood, considering the importance of both natural and cultured pearl, and shell fisheries (Gervis and Sims, 1992). P. imbricata radiata is an epifaunal suspension feeder of the subtidal zone and a fouling species, living attached by its byssus to hard substrata. Its maximum lifespan is 8 years, although older specimens have been found. Growth studies have been conducted in populations of this species in the Red Sea (Yassien, 1998), Qatar (Mohammed and Yassien, 2003), India (Narayan and Michael, 1968; Jeyabaskaran et al., 1983), Japan (Wada, 1991), Taiwan (Hwang et al., 2007) and in the Mediterranean Sea (Yassien et al., 2000). Usually it attains a length of 50-65 mm. Maximum observed shell length was 93.2 mm in the Red Sea (Yassien, 1998), 64.0 mm in the Mediterranean Sea (Yassien et al., 2000), and 100.0 mm in Japan, on an individual with a ten year lifespan (Wada, 1990). Mohamed et al. (2006) concludes that the biotope and P. imbricata radiata’s interaction with the environment are important determinants of growth and shell dimensions.


The number of chromosomes for P. imbricata radiata according to Ieyaba and Inaba (1974) is n=14 and 2n=28. The gross morphology of the chromosomes of this species has been reported by Wada (1976), and its karyotype by Komatsu and Wada (1985). The molecular phylogeny of pearl oysters and their relatives has been studied by Tëmkin (2010) and Cunha et al. (2011).

Temkin (2010) found that there were low levels of molecular divergence between these populations and chose to regard this group as a single species with three subspecies; P. imbricata imbricata, P. imbricata fucata and P. imbricata radiata. The shells of this Pinctada complex are variable; differentiation of the subspecies can be difficult and are recognised by their location rather than morphology.

In contrast, according to Cunha et al. (2011), molecular analyses question the taxonomic validity of the morphological characters used to discriminate P. fucata and P. martensii that exhibited the lowest genetic divergence and are most likely conspecific as they clustered together. P. radiata and P. imbricata were recovered as monophyletic.

Reproductive Biology

Publications on the reproductive biology of P. imbricata radiata include those of Herdman and Hornell (1906), Malpas (1933), Tranter (1959), Khamdan (1998) and Zouari and Zaouali (1994). The spatial and temporary variation of juveniles this species has been studied by Castellanos and Campos (2007).

P. imbricata radiata is a protandric hermaphrodite species with sex inversion occurring in shells of 32-57 mm (Zenetos et al., 2004a). Sexual dimorphism is absent, and in contrast to other species of the same genus, the colour of the gonad is an unreliable aid in sex determination (Khamdan, 1998). The morphology of the gonad, which is not a discrete organ, is similar to other species of the genus Pinctada (Khamdan, 1998). Gonad maturity is controlled by temperature (Zouari and Zaouali, 1994).

Both oogenesis and spermatogenesis occur in similar timing, i.e. commence in winter and continue through spring. Thus, the breeding cycle in this species is seasonal with two peak spawnings in the summer and autumn (Khamdan, 1998; O’Connor et al., 2003). In the Persian Gulf and the Red Sea, the spawning of adult P. imbricata radiata is reported to be essentially continuous since there are always at least a few spawning individuals present throughout the year (Khamdan, 1998; Yassien, 1998). In other areas however, this is not the case. Microscopic examination of the gonad in P. imbricata radiata individuals from southeast Australia (O’Connor et al., 2003) indicated differences between the two peaks: samples collected following the summer peak showed a high proportion of empty gonads, consistent with spawning, while those taken in autumn suggested that the oysters were resorbing the gonad rather than spawning. The same study (O’Connor et al., 2003) showed a significant variation in the numbers of spat settling, and that settlement was restricted to the summer months. This is consistent with summer spawning and further suggests that the second, autumnal peak in reproductive activity does not contribute to oyster settlement (O’Connor et al., 2003).

Although salinity levels have been suggested for controlling spawning (Malpas, 1933), it seems that temperature is more likely to be the controlling factor (Khamdan, 1998).

Environmental Requirements

In Japan, favorable temperatures for adult P. imbricata radiata oysters have been reported to lie within the range 13-25ºC, while temperatures outside the range 7-29ºC are considered critical (Wada, 1991). Furthermore, spat of 3 mm were found to be intolerant of temperatures less than 17.5ºC, with a suggested lower limit of 15ºC (Numaguchi and Tanaka, 1986a). In controlled temperature experiments on P. imbricata radiata, a total failure of embryos to develop to D-veliger stage at 14ºC, and rapid onset of juvenile mortality in temperatures <14ºC and >26ºC were reported (O’Connor et al., 2003). The influence of temperature on growth was studied in India by Pandya (1976) who reported that P. imbricata radiatahas a higher growth rate at temperatures between 19 and 28ºC than at 28 to 32ºC. Wada (1991), notes that differences in temperature tolerance may vary with geographic area.

As with temperature, salinity tolerances reported for P. imbricata radiata appear to be a function of a number of factors including geographic location and ontogeny(O’Connor et al., 2003). In Japan, long-term studies reported the minimum salinity optimum for spat to be 22.7 g kg-1 (Numaguchi and Tanaka, 1986b), while in India adult P. imbricata radiata have been found to be tolerant of salinities within the range 24-50 g kg-1 for 2-3 days (Alagarswami and Victor, 1976; Dharmaraj et al., 1987a). In Australia, P. imbricata radiata embryos failed to develop to D-veliger stage at salinities of 26 g kg-1 or less, byssal attachment by juveniles did not occur at salinities of 17 ppt or less, and high mortality occurred at salinities of 23 ppt or less within 7 days (O’Connor et al., 2003).
There is little information regarding interactions of temperature and salinity on pteriid oysters. In general, extremes in one factor reduce tolerance to variations in the other (synergism), although one factor can influence responses more rapidly than the other (O’Connor et al., 2003).


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Am - Tropical monsoon climate Preferred Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
30 30

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Depth (m b.s.l.) Optimum 0–150 tolerated
Water temperature (ºC temperature) 13 25 Optimum 7–29 (Wada, 1991)

Notes on Natural Enemies

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Natural enemies of P. imbricata radiata include fish, predatory flatworms, sponges (Cliona spp.), and shell boring spionid polychaetes (Polydora and Boccardia spp.) (O’Connor et al., 2003). Reports attributing damage and mortality in P. imbricata radiata to spionid polychaetes are common and have arisen in areas such as Sri Lanka (Herdman, 1903), Japan (Mizumoto, 1964), India (Dharmaraj et al., 1987b), the Persian Gulf (Doroudi, 1996) and China. Spionids are thought to “fatigue” the host pearl oyster (Wada, 1991) and weaken their shells, increasing their susceptibility to predators.

Predatory gastropods, Cymatium parthenopeum and members of the same genus have previously been implicated in farmed pearl oyster mortality (Chellam et al., 1981; Friedman et al., 1998; Urban, 2000). Observed high rate of mortality in P. imbricata radiata in the Persian Gulf (Doroudi, 1996) was attributed to the predation of species such as boring mussels (Lithophaga malaccana and Lithophaga hanlyana) and boring sponges (Cliona carpenteri, Cliona margaritifera and Cliona vastifica).

Boring and fouling organisms have been known to cause mortality in P. imbricata radiata observed at different growth stages (Mohammed and Yassien, 2003).   

Trematode species belonging to the family Bucephalidae have been reported to parasitize on P. imbricata radiata, causing the destruction of female gonads and resulting in reproductive failure (Ngo and Choi, 2004).


Means of Movement and Dispersal

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Natural Dispersal

The pelagic larvae of P. imbricata radiata are dispersed by water currents (DAISIE, 2009) and its distribution in the Mediterranean Sea implies that the progressive penetration of this species is mainly caused by natural dispersal (Dogan and Nerlovic, 2008).

Vector Transmission

There is a record of P. imbricata radiata individuals attached as epibionts to the shell of a loggerhead sea turtle (Carretta carretta) in the Mediterranean Sea (Oliveiroet al., 1992).
Winston et al. (1997) recorded Pinctada attached to marine litter off the coast of Florida. Holmes et al. (2015) reported it on macrolitter: three specimens, attached to a plastic spool, Chesil Beach, Dorset, UK, and one shell, in a bait pot, Loher Beach, Waterville, Co Kerry. Ireland.

Accidental Introduction

Accidental occurrences of P. imbricata radiata have been recorded in Toulon (France), where the species was scraped off the hull of a naval ship (Zibrowius, 1979), and in the port of Trieste (Italy) as live individuals attached to an oil platform originating from the Strait of Sicily (Vio and De Min, 1996).

Intentional Introduction

There is documentation that P. imbricata radiata was intentionally imported for aquaculture purposes in Greece and Italy during the 1960s and 1970s (Serbetis, 1963; Zenetos et al., 2004a).


Impact Summary

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Economic/livelihood Positive
Environment (generally) Negative

Economic Impact

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P. imbricata radiata has long been in use for the production of pearls and is also an edible mollusc species. There are generally no negative economic impacts caused by P. imbricata radiata. The only relevant report is that it fouls mussel lines and commercial shellfish collectors (DAISIE, 2009).

Environmental Impact

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No specific impact of P. imbricata radiata on either habitats or biodiversity has been cited in the literature (Streftaris and Zenetos, 2006). However, there is insufficient information concerning its role in affected ecosystems. This bivalve is considered to be a habitat-modifying, gregarious species capable of impacting native fauna by forming oyster banks (DAISIE, 2009).

Studies conducted in Tunisia to test for a possible community shift from a substrate without Pinctata and a substrate with initial low density Pinctada settlement, were not conclusive. Results may not confirm that the community structure variability is due to the impact of Pincata invasion because the potential and subtle community shift may be masked by the overwhelming influence of just the local environmental gradients. In spite of this, the introduced oyster may play the role of an engineer species at high densities, contributing to the complexity of the benthic habitat and influencing the trophic pattern of its fauna (Tlig-Zouari et al. 2011).

Social Impact

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No impact of P. imbricata radiata on human activities has been documented.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Pioneering in disturbed areas
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Gregarious
Impact outcomes
  • Modification of natural benthic communities
  • Reduced native biodiversity
Impact mechanisms
  • Fouling
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately


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Economic Value 

The rayed pearl oyster P. imbricata radiata is the pearl oyster with the longest history of sustained harvesting (Mikkelsen, 2003). It has been fished for its pearls for centuries and is amongst the widest spread of the pearl oyster species. It is collected in many areas of the Indo-West Pacific for its edible muscle, nacreous shell and ability to develop pearls (Carpenter and Niem, 1998). P. imbricata radiata has been produced in hatcheries in Asia for decades and it is considered among the most robust of the genus for this purpose (Ito, 1998). It is a major economic species for pearl production in India, Sri Lanka, Myanmar, China, and Japan (Carpenter and Niem, 1998) and the main areas of production are Japan, China and India (Berthou et al., 2009). It is also actively cultured in Australia, Hawaii, Indonesia and Vietnam (CIBJO, 2006).

In China, although the history of the exploitation of saltwater pearls extends as far back as 200 BC, it has only been for the last 30-40 years that the interest has extended to farming pearls in the marine environment. Culture has been limited to the southern provinces of Guangxi, Gaungdong and Hainan (O’Connor et al., 2003). In Japan it is actively cultivated and has formed the basis of a billion-dollar pearling industry. A drastic and continuing decline in Japanese production of high quality pearls and pearl shell (e.g. from 118 000 kg in 1993 to 63 000 kg in 1996) due to the degradation of inshore waters (as is also the case in China) and disease, has created a large gap in market supply of this class of pearl (O’Connor et al., 2003).

P. imbricata radiata is also economically important in the Persian Gulf area, the Red Sea, and the Mediterranean Sea. In Qatar it represents about 95% of the total oyster catch (Mohammed and Yassien, 2003), in Saudi Arabia it supports artisanal fisheries (Gladstone, 2002), and in Lebanon it is considered a species with economic value, being exploited in the Sarafand area (Nader and Talhouk, 2002). It is also of minor commercial interest in Greece (Koutsoubas et al., 2007).

Social Benefit

P. imbricata radiata is an important protein source and thus has an important role in human nutrition (Gokoglu et al., 2006). It is an edible mollusc species that is consumed in many countries and areas around the world, i.e. Qatar (Mohammed and Yassien, 2003), Lebanon (Nader and Talhouk, 2002) and Egypt (Farag et al., 1999).

Environmental Services

Pearl oysters have been used extensively in contaminant screening surveys (De Mora et al., 2005) because of their ability to accumulate high concentrations of metals (Talbot, 1985; Paez-Osuna et al.,1993;) and lipid soluble pollutants (Dunbar et al., 2003) in their soft tissues. These organisms can be used as bioindicators of marine metallic pollution (Elder and Mattraw, 1984) because they can accumulate metals in their tissues in proportion to the degree of environmental contamination (Lopez-Artiguez et al., 1989; Hamed and Emara, 2006).

P. imbricata radiata oysters have been specifically used as bioindicators for heavy metal pollution in numerous regions around the world, notably the Persian Gulf (Sadiq and Alam, 1989; Al-Sayed et al., 1994; Bou-Olayan et al., 1995; Madany et al., 1996; Al-Mafda et al., 1998; Zainal et al., 2008) and Australia (Gifford et al., 2005a; Giffordet al., 2005b; Linz et al., 2005; Gifford et al., 2006), but also Turkey (Goksu et al., 2005). MacFarlane et al. (2006) reports that the shell of P. imbricata radiata may be employed as a suitable biological exposure archive for lead (Pb), while Gifford et al. (2006) indicates that it is relatively tolerant to lead (Pd) and zinc (Zn), and could be deployed within a remediative context in moderately polluted coastal areas.

P. imbricata radiata have also been used as biomonitors for other types of pollutants, namely organotin (De Mora et al., 2003), hexadecane and octocosane (Gifford et al., 2006), polychlorinated biphenyls (Mahaseneh and Al-Sayed, 1994), and chlorinated hydrocarbons (Mahaseneh and Al-Sayed, 1994). De Mora et al. (2005) reports that this species presents one of the best possibilities to make sub-regional comparisons of chlorinated hydrocarbon levels.

P. imbricata radiata, being a commercial species with wide distribution, is an ideal tool for pollution biomonitoring. Its distribution allows for the collection of comparable data from different regions, and proven hatchery techniques can allow production of large numbers of genetically similar animals of known ages for use in trials (Sarver et al., 2003).


Similarities to Other Species/Conditions

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This species is hard to distinguish from shell appearance only. It looks very similar to Pinctada margaritifera, from which it differs in size, colour and shape of the adductor muscle scar (Zenetos et al., 2004a). The shell of P. imbricata radiata is smaller and thinner, and its outer shell coloration differs from P. margaritifera in that it is tan-coloured (in contrast to greyish green) and its markings are reddish to black (in contrast to white or yellowish) (Oliver, 1992; Zenetos et al., 2004a).

Gaps in Knowledge/Research Needs

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Being an important economic species, the biology and ecology of P. imbricata radiata have been extensively studied. Also, because of its long history as an intensively cultured marine species, most aspects of its reproduction and growth are well documented. However, there is little information in the literature concerning its status as an invasive species. Its effect on habitats and biodiversity is poorly studied, and not yet fully understood. More research on its rate of invasion, especially in the Mediterranean Sea is needed. Furthermore, information concerning its interaction with native species of invaded areas, and its role in trophic relations is definitely required.


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Monaco: CIESM - Commission Internationale pour l'Exploration de la Mer Mediterranee, Villa Girasole, 16 bd de Suisse,

USA: OBIS - Ocean Biogeographic Information System, 71 Dudley Road, New Brunswick, NJ 08901,


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13/02/16 Updated by:

Argyro Zenetos, Institute Marine Biological Resources and Inland Waters, Hellenic Centre for Marine Research, P.O. BOX 712, Anavissos 19013, Greece

08/07/09 Original text by:

Argyro Zenetos, Institute of Oceanography, Hellenic Centre for Marine Research, P.O. BOX 712, Anavissos 19013, Greece

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