FEEDING AND REARING FISHES. 
307 
winter in a warm room; others he kept in the Pharmacological Institute in a room not heated, hut not 
exposed to frost; others, again, since January, at the Physiological IvaI)oratory for Animals at the 
Academy of Toppelsdorf, near Bonn, in a room exposed to all atmospheric changes. (i)ne set of the 
aquaria was prepared as called for by Weeger; that is, 10 cubic centimeters of garden soil were 
placed on the bottom and soaked with liquid manure; on this was placed mud from the puddles 
containing crustaceans, and on this, again, dry leaves of hazelnut and willow trees. The aquarium was 
then filled up with water. Some tiliform alg®, iVoJffia, and other small water plants had entered into 
the aquarium with the mud. In the course of two weeks there developed in all the aquaria minute 
crustaceans (shell insects, flea lobsters, water multipedes, infusoria, green algre), a felted mass of 
filiform algre, and a thick cover of Wolffia. The warmer the aquarium the quicker and better was the 
development, hut the jilant life seemed to prosper better than the animal life. By catching these 
small crustaceans in proper iiijiettes it was shown that the quantity in the aquarium was less than in 
running water. 
Subsequent exi^eriments jiroved that the majority of the Crustacea were very easily affected by 
even the smallest quantity of ammonia, sulphureted hydrogen, or free acids, as also stated by Weeger. 
It is clear that only the most favorable conditions for the development of the Crustacea in the aquaria 
prei^ared according to Weeger are mentioned. Then comes a xieriod, which passes quickly, develop- 
ing a good deal of this animal life. Dr. Kochs tried to accelerate the increase by throwing in small 
pieces of meat or dung, sometimes with more or less success, and to raise larger individuals, having 
the most success with the water multixiedes. 
These exxaeriments soon convinced him that water in which the Crustacea grow well and increase 
was too unclean for most fishes; moreover, the Crustacea require warm and more or less stagnant 
water, and can, therefore, only he raised in shallow puddles exjaosed to the sun and coutainiug many 
water jdants, whereby it is clearly shown that the x>i’ox>agation of infusoria for fish food must bo 
entirely sexiarated from the breeding of fishes. When attemx^tiug to breed both in the same vessel, 
either the water fauna ijrosper and in that case the fishes can uot live, or vice versa. He ascertained, 
also, through special experiments, that the minute Crustacea could hardly live in water most favorable 
for the growth of niicroscor>io x)lant life. 
MixingO.l liter of nitrate of ammonia, 0.1 liter of bix)hosxihate of potash, anda minute quantity 
of iron with the strongly calciferous water from the city hydrant in Bonn, and adding a small 
numlier of water |)lants, the water will soon turn strongly green and turbid at a temiierature of 
from 10*3 to 12° C. (50° to 51° F.), and becomes slimy on account of the algaj. Daplniia and Cypris 
will hardly grow therein. 
His aim to first produce, in the xirojaer manner, large quantities of greenish water rich in jilant 
life for the sustenance of the Crustacea x>roved a failure. Still it is true that many Crustacea live 
on microscopic plants, but the most favorable condition of life does uot tally with that of the jilauts. 
The Crustacea are only good in transparent and clear water; all the fine aquaria tested for years 
contained large water xilants, hut also always clear water. 
Later he experimented as follows : 
To make the method to breed Crustacea artificially x>racticable and feasible the material needed 
must be easily accessible and cheap. If the breeding is done in simcial recexitacles (reservoirs) it must 
be done in such a way that it will be easy to get the infusoria clean when fed to the fishes. The fol- 
lowing experiment led him to a procedure which in his opinion will prove successful : Taking two glass 
vessels each containing 10 liters of water (21.13 iiints) and adding 100 grams (3.53 ounces avoirdiqjois) 
of fresh cow manure without straw in such a way that in one vessel this mannre is evenly distributed, 
while in the other these 100 grams of manure are jilaced in a glass cux> and covered by wire netting, 
it will soon he observed, esxjecially where the temperature is warm, that a strong decomposition takes 
place in the first-mentioned ve.ssel, a thick scum of bacteria is formed, the li([uid turns light-brown 
and smells strongly of musk and ammonia. Cypris and JJapIniia may live, and even increase, in this 
bad-smelling liquid, if the temperature is not too high, and under the described conditions. On the 
other hand, there is hardly any smell in the second A'essel, where the manure is inclosed in the cup. 
The gases forming in the manure raise the cup, bottom upward, to the surface of the water, which is 
soon covered with a scum consisting of numerous bacteria and infusoria. The outer side of the wall 
of this cup, and also the bottom of the large vessel, is soon covered with a whiteslime, also consisting 
of bacteria and infusoria. After some time only organisms are developed containing chlorophyl 
(green coloring matter of leaves or j)laiits) in large quantities. Daphnia, Cypris, Cyclops, and many 
other Crustacea grow finely in such a vessel. The wire netting which prevents the cow manure from 
mixing with the water is thickly covered with minute Crustacea searching for food. As the water 
