The white sardine (Escualosa thoracata) is a species of fish in the family Clupeidae. It is a tropical fish of the Indo-Pacific distributed from Thailand to Indonesia and Australia. Other common names include deep herring and northern herring.

This species is amphidromous. It is known to swim at a maximum depth of 50 metres.

The largest known standard length for the species is 10 cm.  It is distinguished from its sister species, Escualosa elongata, the slender white sardine, by its deeper body and broader silver band. The white sardine feeds on zooplankton and phytoplankton. It is a commercially important fish, used fresh and dried

LIFE-HISTORY

EGG

• The egg of the white sardine is the most abundant fish egg in the coastal waters of West Hill.

• It first appears by October and continues till February, but the November- January portion of the period is the best when it occurs in enormous numbers to constitute the bulk of the fish eggs in the plankton.

• The eggs are pelagic, transparent and perfectly spherical with the diameter varying in the living condition from 0.7 to 0.8 mm.

• The yolk is transparent and spherical and shows distinctly the vacuolation characteristic of clupeoid eggs.

• A fairIy wide perivitelline space is present.

• Shining transparent spherical oil globules are present in the yolk mass and their number usually varies from six to eight.

• The oil globules show a tendency to crowd on the ventral periphery of the yolk mass.

EMBRYONIC DEVELOPMENT

• The embryo is well formed and occupies a little more than half the circumference of the yolk mass. The eyes, otocysts and the heart have formed, though the last is not yet functional.

• The myotomes have also differentiated and about eighteen of them are present in the embryo in this stage. Unlike other clupeoid eggs, pigment is laid in the white sardine egg even in the early embryonic stage in a characteristic manner.

• 'Black unbranched chromatophores have formed and these are scattered uniformlv on the dorsal side of the developing embryo.

• when the egg is ready for hatching. At this stage the embryo occupies about three-fourths of the circumference of the yolk mass and performs frequent twitching movements inside the egg membrane with the aid of the caudal portion which is free from the yolk mass .

HATCHING

• The abundant occurrence of the eggs has made it possible to make a close study of the process of hatching which is rapid and takes only a very short time.

• The first sign of hatching is the slight, but quick, elongation of the spherical yolk mass along the embryonic axis to assume a cylindrical shape.

• The two rounded ends of the elongated yolk mass press against the egg membrane which becomes stretched, losing its spherical shape.

• The egg membrane splits open at the region of the head owing to the gentle pressure exerted by the elongated yolk mass. The opening thus formed is large enough for the head to be thrust out, but the aperture enlarges by the side to side twitching movement of the larva.

• The larva slips out quickly through this widened opening up to the caudal portion and by a few lashing movements of the tail rids itself of the shrivelled egg membrane.

NEWLY HATCHED LARVA

• The newly hatched larvae are very inactive and float on the surface of the water upside down due to the buoyancy of the yolk and its oil globules. They measure 1.5 mm in length.

• The ellipsoidal yolk mass occupies about half the length of the larva .

• The free caudal portion of the newly hatched larva is curved but becomes straight gradually in about an hour.

• The myotomes are distinct and about forty-two of them are seen in the newly hatched larva.

• The alimentary canal is long and straight and the vent which is situated far behind the yolk mass opens to the exterior below the thirtyfourth or the thirty-fifth myotome.

• The fin-fold is continuous and entire and originates dorsally from the anterior third of the larva.

• No change in the pigmentation from that of the embryo is noticed, except an increase in the number of black chromatophores which are uniformly scattered over the entire dorsal side of the larva.

DISTRIBUTION

• The white sardine, Kowala coval, which is easily distinguished by its yellowish-white colour and silvery lateral band, is a widely-distributed species attaining a maximum size of 13. cm and is recorded from India, Pakistan, Ceylon, Burma., Malaya, Malay Archipelago and China.

• It is a shoaling species inhabiting the shallow coastal waters. Shoaling in vast numbers is known only from the West Coast of India.

DIET

• The food of the White sardine consists exclusively of plankton.

PARASITE

• An unidentified cymothoan ectoparasite has been frequently noticed under the operculum of the white sardine.