26 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



in the trencli beyond the diaphragm to intercept such coarser materials, 

 along- with which a good deal of pretty fine sediment would be caught 

 and prevented from clogging the diaphragm. If one diaphragm failed 

 to accomplish the desired result, two placed in the same trench in 

 succession could not fail to answer, and it would then doubtless be possi- 

 ble to completely arrest all sedimentary materials as well as effectually 

 prevent the escape of any brood in the outflow which it was desirable 

 to confine in the inclosure. 



Such in the main are the conditions to be fulfilled in the construction 

 of artificial oyster ponds. In Fig. 5 the conditions are essentially those 

 obtaining at Stockton. The shell collectors consisted of perforated 

 oyster shells strung upon wire and hung upon the stakes s s s .s s, as 

 shown in the figure. Shells were also strewn upon the bottom, but in 

 practice these ponds ought also to be available for the culture of adult 

 oysters both for market and breeding purposes, and if the pond is pre- 

 l)ared with the proper bottom, supplied with water of the right density 

 and temperature and with the proper amount of oxygen in solution, there 

 is no reason why success should not reward the experimenters. In 

 Europe the claires are often constructed so as to have their bottoms at 

 about low-tide level, so that they may be drained and cleaned. This 

 would hardly be practicable along the eastern seaboard of the United 

 States because the rise and fall of the tide is, as a rule, not great enough. 

 But this need not be any obstacle in the way of success, for in the Re- 

 port of the United States Fish Commissioner for 1880 there is a transla- 

 tion of a Norwegian notice, by Prof. H. H. Rasch, of a natural basin near 

 Stavanger, Norway, in which oysters are indigenous. This lake, strange 

 to say, ''lies a few feet higher than the open sea close outside of it, which 

 could convey saltwater into the lake only during severe southwest storms 

 combined with spring tides. The lake receives through a brook the sur- 

 plus fresh water from two lakes situated higher: " it has a percentage of 

 saline matter ranging from 0.02 to 3.90 per cent. — the former at a depth 

 of 2 feet, the latter at 27 feet. The oysters thrive best in it at a depth 

 ranging from 3 to 15 feet ; in this so-called oyster belt swarms of young 

 oysters appear to congregate during at least nine months of the year. 

 In 1879, 65,000 young oysters of the European species were taken from 

 the lake, scarcely five acres in area, a quantity which would be equiva- 

 lent to about 430 bushels of the American species. These young ones 

 were transplanted to fattening grounds. 



This lake is protected by clifls around three sides 300 to 400 feet high, 

 which defend it from the cold winds of this inhospitable northern region. 

 Algce grow in the lake, and, with its relatively uniform high tempera- 

 ture in its protected situation, aifords probably amongst the very best 

 conditions for the growth of oysters. 



We know very well that it is quite out of the question to attempt to 

 control the character of very large bodies of water so as to adapt them 

 to the purposes of the oyster culturist, but if nature has in a few in- 



