Observations on the life-history of the Indian shad,Hilsa ilisha (Hamilton)

Abstract

The available information on the life-history ofHilsa ilisha (Ham.) is given briefly and discussed. The collections of eggs and early larvae from the Hooghly River in West Bengal and from the Daya River (Orissa) are recorded. The spawning habits are given. The unfertilized egg which is 0·70 to 0·75 mm. in diameter, is almost spherical, transparent and demersal though it contains many oil-globules. A fair-sized femaleHilsa is estimated to contain 1 million eggs. Spawning seems to take place generally towards the evening. Stages of embryonic development up to the time of hatching are figured and described. At a water temperature of about 23° to 25° C, the egg hatches in about a day. The eggs hatch out just as well in 1% normal salt solution and in ordinary chlorinated tap water as in the river water. The newly hatched larva is 2·3 mm. long. The larvae lived under laboratory conditions for a maximum period of 5 days attaining a length of 5·6 mm. Yolk is completely absorbed when it is about 8 mm. long. The larval development of the fish till it becomes a juvenile is described and figured. From available records it appears that growth during the first year is roughly at the rate of an inch per month. Our observations show that the fish descend into the sea during the first year of their life. The need for further study on the bionomics of the fish is indicated. The great damage done to theHilsa fishery by the capture of the countless fry and fringerlings of the fish in the tidal areas is stressed and the urgent need for the protection of the fry and the early stages is emphasized. The desirability for a proper survey of the spawning grounds in the rivers and further investigations into the fate of the egg and the larvae that drift down the estuary is indicated.