No. 6 (1921) COMMON MOLLUSCS OiF SOllTH INDIA 1/3 



particularly those in the Sonapiir backwater, where the Bairavi 

 men are accustomed to visit the beds at low water, break open the 

 shells and carry away the flesh in chatties to use in their own 

 curries. 



St'dsons and spawning.— ^The season when oysters are in market- 

 able condition depends upon the time of spawning and this in turn 

 is controlled by rainfall and sunshine. Heavy rains causing flood 

 water to enter backwaters in such amount as to greatly lower the 

 salinity of the water over the beds invariably entails wide-spread 

 and immediate emission of the reproductive products in all oysters 

 where the gonads are well filled. Hence as the rainy season 

 differs on the two main coasts of India, there is a corresponding 

 divergence in the spawning maxima and in the marketable season 

 in these two localities. 



On the Malabar Coast the chief spawning maximum occurs 

 about midsummer or even earlier, at the onset of the south-west 

 monsoon and the oysters are not again in condition till October or 

 November. From this time onwards they improve in quality till 

 about the end of March ; thenceforward till the final and complete 

 spatting at the end of May or early in June, there is a good deal of 

 irregular spatting induced by the hot weather then prevailing, 

 emphasized by the exposure and semi-drying of many of the oyster 

 covered rocks during the low-water of the major spring tides. 

 Between March and June a considerable percentage of spent 

 oysters are always found in any number examined ; the gonads of 

 those that spawned early in March will be partly full again when 

 the floods arrive in June and these, after enduring the lowered 

 salinity of the water for a while, will at last emit their spawn 

 though perhaps only half mature. Long continued floods cause 

 very extensive mortality on the beds, and few survive except the 

 small number living on the bottom of deep channels. In these 

 places saline conditions appear to last much longer than on the 

 surface, the lighter specific gravity of flood water causing it to 

 pass over the deeps without clearing out completely the saline 

 water which was there before the onset of the floods. Spawning 

 in the case of these few surviving oysters appears to be deferred 

 till about August when the floods have partly subsided and tidal 

 conditions are re-established. Much variation exists however in 

 this cycle of events, for under normal conditions the common 

 Indian oyster is a most irregular spawner; except when the floods 



