206 BULLETIN OF THE UNITED STATES FISH COMMISSION 
becomes clouded with swarming millions of their progeny. The fecal 
matter dropped, by the fish during their month of occupancy is suffi- 
cient to maintain the fertility of the bottom, and thus the system, once 
established, becomes automatic and self-sustaining. 
A single attendant can have the care of a large establishment, his 
only duty being to drive the fish periodically from one feeding ground 
to another and close the gate behind them, as a farmer changes his 
flocks from one pasture to another. 
It remains to be explained that while the Daphnia , Nais, Cyclops , and 
other extremely delicate species can be profusely grown only in still 
water, the fresh- water shrimp ( Gammarus pulex) grows abundantly in 
living streams. At Gremaz, rivulets are provided which flow from the 
springs into the tanks and carry away the overflow. These rivulets, 
the bottoms of which have been impregnated by the Lugrin system, 
are filled with cresses and other water plants and produce the minute 
shrimps in such abundance that they are gathered daily in panfuls by 
a few sweeps of a gauze scoop-net and fed to the fish in the swarming 
tanks. This part of the process is easily applicable to natural streams 
where a sufficiency of food does not already exist. 
As to the applicability of this system to American pisciculture, there 
is apparently no room for doubt or question. The same natural condi- 
tions which exist at Gremaz can be found in nearly, if not quite, every 
State in the Union. The same food which is produced there may be 
used in growing nearly every species of fish which is artificially reared 
in the United States. American brook trout, the rainbow trout and 
California salmon thrive admirably in the tanks at Gremaz. 
To conclude with the verdict of Prof. Francis Day, who, in October 
last, came specially from England to investigate and report upon the 
system which has been so successfully established there : 
u When I remark that a tank, 35 meters long by 3 broad, and 40 
centimeters deep, and capable of containing 20,000 young trout, can be 
fully stocked with food in fifteen days, so as to be able to sustain the 
residents for one month without any additional supply, I can not help 
thinking that Mr. Lugrin has solved a difficult problem, and that his 
mode of cultivating the natural food of fishes will prove a great and 
lasting benefit to fish culturists.” 
Marseilles, February 25, 1888. 
