Flow to obtain it. 205 
much of the nature of their food as to become highly poisonous 
to the fish, when their food, or the water in which they live, is of 
an unwholesome character. There is here a very wide field for 
research, for which we want some workers. 
As already stated, the plan to adopt for the cultivation of this 
class of food is, first of all, to protect them from their enemies. 
As trout are their enemies by nature, therefore they must be 
protected from them ; and this brings us to the point of having 
separate or accessory ponds in which to cultivate a sufficient’ 
amount of food. At Gremaz, in France, the food is cultivated, 
and the fish are herded from pond to pond, very much as sheep 
are penned off on turnips, and are moved from one pen to another 
as the crop is devoured. What I conceive to be a better way, 
and one that I have adopted for many years, is to grow the food 
in separate ponds, to which the fish have no access. 
Either plan may be equally good, and probably is so. It 
just resolves itself into a case of which is most workable. In our 
cold northern climate we must adapt ourselves to circumstances. 
With these ends in view, an excellent plan, then, is to provide 
special ponds, well stocked with plants, for the production of the 
natural food of the trout. In this way a natural supply may be 
obtained, and maintained, but if once the trout gain access to the 
food pond, the result will probably be the entire depletion of the 
stock of fish food. 
One of the best animals to cultivate is the water flea 
(Daphnia). Though so called, yet it is not in reality a flea, although 
in general appearance it bears some re- 
semblance to Pudlex irritans, its “longshore” 
namesake. ‘There are some ten varieties, 
varying in size from three sixteenths to one 
sixteenth of an inch in diameter. The 
commonest species is Daphnia pulex, which 
varies in colour and size considerably, accord- 
ing to the nature of its surroundings, and also 
to the time of year. It is semi-transparent, 
and usually of a reddish tinge, and swims 
with a jerky movement ; its food consists of small znfsorta and 
vegetable matter. It thrives best in moderately still water, and 
Fig. 23. 
Daphnia pulex, enlarged. 
