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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
impossible for them to open ; yet growth and fattening under these conditions was in 
every way noteworthy. In localities where the proportion of normal food organisms 
is naturally high, a greater quantity of oysters can be raised in a given water volume, 
e. g., Soudre, Whitstable, Ostend. In such localities the naturally high food normal 
may be artificially increased by conditions of claire culture, where a given volume of 
water is retained in ponds and given the best conditions for rapid increase of diatom 
life. Warmth, richness in plant food (Marennes), and a proper degree of salinity 
may give the forcing conditions of what might be likened to greenhouse culture. In 
some instances a remarkable number of oysters may be fattened in a fixed bulk of 
water. At La Tremblade so favorable are the conditions that in the shallow claires 
(whose water is renewed but once a fortnight, and whose depth averages less than a 
foot) fifty oysters are normally fattened to the square yard of bottom. 
In regions where the waters do not contain a high percentage of food organisms, 
culture in closed ponds is clearly unprofitable, as the Avater is both low in food normal 
and limited in volume. In instances of this kind it is understood that the two essen- 
tial conditions, degree of temperature and salinity, have remained practically com- 
parable ; otherwise it is evident that from these causes, as much as from actual lack of 
food, the oysters may be restricted in growth. The instance that Mdbius cites, that 
of the oyster reservoir at Hayling Island, as demonstrating that the oysters had 
exhausted the food supply and remained dwarfed in size, may, judging from the 
character of the locality, not improbably have been the result, and the sole result, of 
an exceeding saltness of the water. At Auray, in the neighborhood of the natural 
grounds, Mobius states that far more seed oysters are raised than can ever be grown 
to marketable size, on account of lack of space and food resources. Judging from 
what is now being done at Auray, the industry is profitable as purveying seed oysters 
for the parks in regions (e. </., in Brittany) unfavorable to production. The experience 
of the Auray culturists does not favor the idea that the lack of oyster food limits 
elevage , but that efforts at collection are of greater advantage commercially. 
The law of oyster growth, as stated by Mdbius, seems, therefore, from the stand- 
point of the culturist, open to misconstructions: “ Oysters are to be included in the 
same list with other animals; the sum of their entire mass is dependent upon the 
amount of food stuff Avhich they obtain and store up,”* becomes truism. This might, 
however, be thought to imply that the number of oysters in a given river or bay might 
not become greater because their biocoenose appears to be perfect. Artificialization 
has demonstrated that the matter of food supply in natural oyster localities is of far 
less importance than space for culture and immunity from enemies. 
Mdbius, discussing the possibility of success in the French cultural system, con- 
cludes “ that in all parts of the Wattenmeer, where oysters could find room and gene- 
rate, there they already live. On all parts between the natural banks the SAviinming 
embryos as they settle, either on account of finding no point of support or through 
unfavorable living conditions, can not exist. The principal difficulties in obtaining a 
set on our (German) coast are those of sand or of mud burial.”! It has already been 
shown that difficulties of this character have been successfully surmounted within 
comparatively recent years in France. 
* Mobius, Die Auster u. die Austernwirtkscliaft, p. 79.' 
t Mobius, Ueber Austern- u. Miesmuschelzucht, p. 43. 
