Page 70 - Records of Bahrain (3) (ii)_Neat

486
Records oj Bahrain
2228

Qais, about Clnru, at the islands of Das, Qarnaiu and Zirko, and
oft the coast of Ituus-al-Jibal between Ras-al-Khaimak and Qhubbat
Ghazirah ; in its habitat the Sadaifiyali resembles the Zanniyah. for it
frequents hard muddy or shelly bottoms in the same depth of water.
The Sadailiyah does not often yield pearls, but those which it produces
are ordinarily large and of fine quality.
The laws which govern the growth of the oyster and the fluctuation Growth and
of oyster colonics in the Persian Gulf are by no means ascertained ;* and variation of
the causes in accordance with which the yield of pearls varies from nurabcrB-
season to season have not been investigated there as they have been in
Ceylon.
It is believed that the Malihflrah increases steadily in horizontal
diameter until the end of the second yeav, when it measures about 2
inches, and that thereafter the rate of its growth diminishes; if •

* The^following facta in relation to tho Coylon poavl oyster, nearly all taken from
Professor W. A. Hordman'a Report on the Pearl Oyster Fisheries of the Gulf of
Manaar, 1903-06, may bo of interest to tho general rcador; it is, of oouvso, uncertain
how far they hold good of tho poarl oyster of the Persian Gulf.
Tho poarl oystor is not kormapkroditic, and tho sex of tho individual, whother
malo or femnlo, is permanently tho same. Tbo numbor of males and fomalcs is
approximately equal, but there may bo a slight propondoranco of males. Tho oyster
i8 gregarious without (distinction of sox, and reproduction takes place by the omission
of the gonerati vo products of malo and femalo into tho surrounding water where they
commingle. Midsummer and midwintor are principal breeding seasons.
Larval development takes place in tho snifaoo wntors. Tho young oyster exists at
first in a freo-swiraming condition, which may ceaso within 5 da.VH of fertilisation of
tho eeg, but is capable, it is believed, of being considerably prolonged ; during this
period the rudiraouts of a shell are acquired.
The next stage is that of “ spat", attaohod as a rule to Algae, either rootod or
floating, or to Zoophytes • but tbo animnl, though now oapablc of fixing itself, is
highly locoinotivo and can creep as much ns an inch- in a minuto. This it doe9
generally in an upward direction, probably from an instinct of avoiding sand ; nor is
it, liko the adult oyster, deterred from movement by light. Tho maximum diamotcr
of the oyster may inoreaso during tbo “ spat" stage from *4 of a millimetre to 1*6
millimetres and upwards.
Tho rate of growth of tho animal during tho first and second years of its lifo is
shown to bo rapid. In tho third year growth becomes much slower, and in tho fourth
year still moro slow ; but tho tbiokness and weight of tbo sholl continue to increaso
greatly even after the cxtornal measurements have bocorno almost stationary. Tho
oyster may be considered mature in its fourth year, when its diamotor measured at
right angles to tho bingo line is about 3£ inches ; it is at its best however in its
fifth ; and it seldom, apparently, survives its sixth year.
The food of the oyster consists of microscopic organisms, both animal and vege­
table ; but, while silt, etc., is rojoctod after being formed into a small pellot, miuute
grains of sand and other non-nutritioue particles aro sometimes swallowed. The natural
position of tho oyster is with tho light or leas con vox valvo underneath and with tbo
posterior edge of tbo shell elevated at an auulo of about 20 degreos ; when undis­
turbed it holds its shell slightly opon with the lips about one-third of an inch apart.
If placed with the undor side uppermost the oyster turns itself ovor by a violent
jerk from a retractile sucker or “ foot” which it is ablo to protrude from its shell to
as much as 2\ inches. By means of this "foot ” the oyster i« also ablo to travel,
though slowly, from one place to another ; while tho " foot " is being advanced the
valves of the *hell aro held widely open, and when it is rotractcd they aro closed with a
snap, a manoiuvre which aids considerably in tho forward movomont. An oyster has
been known to progress 27 inches in this manner in 12 hours. # Tho first enro of tho
oyster when it has attained a suitable position is to attach itself
/<luti„ous thread, generally of more than one strand, to some convenient object, tbo