FEEDING AND REARING FISHES. 
311 
REPORT BY M. CHABOT-KARLEN ON THE VIEWS OF M. EMILE RIVOIRON ON THE 
REARINCx OF TROUT BY NATURAL FOOD.* 
M. Rivoiroii says that the youug trout do not take food except Avhen it is moving in the water ; 
that they do not go to the bottom. Unless great care is taken, which is not always possible, failure 
is certain in the use of artificial food on account of decomposition. Of the natural food M. Rivoiron 
prefers the Daplimas. To rear these lie says : Dig near the side of the stream two, four, or six basins, 
from 10 to 12 meters (about 32 feet and 9 inches to 39 feet and 5 inches) long, by 2 meters (61- feet) 
wide, and It meters (about 5 feet) deeix, according to the number of Daphnias to be produced. Clayey 
soil is preferable, as the water with which the basins are filled will not quickly evaporate. In these 
there should be placed diu'ing March, at the north end, because the basins should be dug as near as 
possible from north to south, one cubic meter (about 1|- cubic yards) of fresh dung (cow dung and 
horse dung mixed). 
Every day the water should he stirred until it takes on a light-brown color, without, however, 
becoming tainted. On this point depends somewhat the success of the microscopic beings that 
during the first days of April should be deiiosited there. At a temiierature of 25° C. (77° F.) each of 
these will give birth every five days to eight others, which in a few weeks will amount to millions. 
They reproduce even at a temperature of 32° C. (about 90° F.), and sustain a temperature of — 6° C. 
(al)out 21° F.). The least shock will kill them en masse. Under no circumstances should the water 
he disturbed, and they should he gathered with the utmost care. This gathering (a sort of skimming) 
can be commenced at the end of April and continued until the end of September. It can he done by 
means of a strainer, which should be brought gently to the surface. Before being given to the 
alevins the Daphnias should be placed in fresh water, in order to rid them of tlie odor with which 
they may be imjiregnated; otherwise they will kill the young fish. It is supposed that the ammonia 
in the rearing basin is the cause. A basin should never be fished to the bottom, and eight or ten daj^s 
should elapse, according as the temperature will have more or less favored the multiplication of the 
Crustacea, before recommencing the operation. When giving them to the alevins the same X)recau- 
tions should be taken with the Daphnias as when collecting them, and it is essential that they should 
be deposited in the water very slowly. A Ixasin of the above dimensions will cost 35 francs, and will 
furnish, from April to September, from 170 to 180 kilograms (374 to 396 pounds, avoirdupois) of 
Daphnias. An aleviii so fed will weigh at six months 6 grams (0.21 ounce), with a length of 6 centi- 
meters (about 2| inches). 
* Made to the National Society of Agriculture of France, July 1, 1885. 
