NOTE 



ON 



AN ATTEMPT TO ASCERTAIN THE PRINCIPAL 



DETERMINING FACTOR IN OYSTER-SPAWNING 



IN MADRAS BACKWATERS 



BY 



JAMES HORNELL, f.l.s. 



In a report dealing with the results of a biological survey 

 of Pulicat lake made in August 1908 with the main object of 

 ascertaining the suitability of this largest of Madras backwaters 

 for the culture of the edible oyster, I arrived at the conclusion 

 that " it is extremely probable that the spawning season of 

 Pulicat ovsters coincides with the onset of the floods in October 

 and November." 



2. It has been noted by observers that the spawning season 

 of oysters in European countries and on the eastern seaboard 

 of the United States is correlated with the marked rise in 

 temperature which occurs in shallow waters along the coasts 

 of such latitudes during the summer months, particularly in 

 June and Julv ; Dr. H. F. Moore of the United States Bureau 

 of Fisheries states indeed that oysters do not begin to spawn 

 on the Atlantic and Gulf of Mexico coasts till the temperature 

 of the surrounding water reaches about 70° F. (not less than 

 67° F.), that it may be assumed that on the gulf coast a heavy 

 discharge of spawn rarely, if ever, takes place much before 

 May 1st, and that spawning in all probability is practically 

 completed by the first week in August. In FraDce, at Arcachon 

 and Auray, spat-collectors are seldom placed in position before 

 the middle of June, the beginning of July being the usual 

 maximal spawning period. 



3. In India conditions differ in many essentials ; the tem- 

 perature of shallow waters scarcely ever falls below the minimum 

 of 67° F., while during May to September it seldom registers 

 less than 80° F. often rising as high as 90° F., yet I was 

 unable to see any evidence that spawning occurred freely during 



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