NATURAL HISTORY OF BRITISH SALMONIDZ. 167 
by them being actually less. On another occasion trout were 
kept for many years in a store.stream, and tested with various 
kinds of diet, when it was ascertained that in some instances 
the ‘increase in weight was as much as nine pounds in four 
years (or from one to ten pounds). 
It is evident from these experiments that fish and grubs 
bear no comparison with insect food in point of nourishment, 
in consequence, no doubt, of the amount of phosphate of lime 
contained in the latter ; and of the insects specially contributing 
to fish food, probably most nutritious of all is the May fly, 
which, when in the larval state, works havoc amongst the trout 
ova on the spawning beds. 
Recent piscicultural experiments have demonstrated the 
great value of the fresh-water shrimp also as an article of fish 
diet, and for feeding young fry on. 
It was once my good fortune to have an opportunity of 
verifying the growth rate of trout when fed upon this insect 
which abounds in almost every stream and ditch where the 
water is not too turbid. In its general structure the fresh- 
water shrimp bears some resemblance to the common sand 
hopper to which it is closely allied, and its movements in 
the water increase the similitude. The author of the ‘ Fresh 
and Salt Water Aquarium’ (the Rev. J. G. Wood, M.A.) says 
they act much like fish in their habit of keeping their heads 
up the stream, and in their general conduct look something 
like the fry of various fish. 
Sometimes they make their way up the stream by clinging to 
the stones and other objects that form the bed of the stream, 
making quick darts forward, and then holding tightly to a stone 
until they choose to make a second dash onwards. When they 
have gone up the stream as far as they think proper they loosen 
their hold and come drifting back again, sometimes rolling over 
and over, but generally contriving to keep their heads pointing up 
the stream. In fact, they appear to amuse themselves by this 
action, just as the gnats amuse themselves by dancing up and 
down in the air. 
The food of the fresh-water shrimp is usually decaying animal 
