CONTINENTAL OYSTER CULTURE. 375 



are immediately used, much may be lost. After immersion, the 

 collectors should be examined fortnightly, and if no deposition of 

 spat has taken place, they can with advantage be taken ashore, 

 quickly dried, and as quickly replaced. Tiles should invariably 

 be dipped in lime and cement ; this facilitates both the adhesion 

 and the removal of the young Oysters. Fascines also should be 

 dipped to give a better surface for adhesion. 



How long, it may be asked, should the collectors be left after 

 the spat is deposited ? The less time the young Oysters remain 

 on the collectors in situ, the less will be the loss inflicted by their 

 enemies. On the other hand, the brood are at first very delicate, 

 and exposure to the air, or the sudden change from the deep 

 water of the breeding-ground to that of the farm, may suffice to 

 kill them. Consequently much experience and prudence is 

 necessary. At Spezia, the time allowed is usually forty, to a 

 maximum of sixty days ; at Arcachon, eight to nine months ; but 

 in this latter case the collectors are taken up and cleaned every 

 three months. 



Another practical consideration in the selection of breeding- 

 grounds relates to the necessary physical conditions of the sea. 

 Both temperature and saltness are important factors in the 

 question of reproduction. Within ordinary limits, the higher 

 the temperature, the greater the quantity of spat emitted. Cold 

 may delay the spatting season, heat will accelerate it. As to the 

 best degree of saltness, it may be said approximately that at a 

 temperature of 68° F. to 86° F. the density of the water should 

 not vary much from 1025. 



Turning now to the question of Oyster-rearing, it appears 

 that, in general, artificial rearing cannot be conducted in the 

 absence of three conditions. First, protection from heavy sea ; 

 secondly, moderately shoal water; thirdly, the presence of a certain 

 amount of fresh water from either spring, river or canal. Wherever 

 these conditions are found, artificial Oyster-rearing is possible. 

 The necessity of the first two conditions is obvious : it is not a 

 question of laying down and withdrawing the Oysters ready for 

 market, but of continual attention and work which is not possible 

 except in calm water of moderate depth. The importance of 

 fresh water for rearing purposes is both negative and positive — 

 that is to say, it is on the one hand necessary to counteract 

 evaporation, which in shoal water, especially in warm climates, is 



