210 How to obtain tt. 
piecemeal, as they are quite helpless when once an oar is disabled. 
Older fry hunt them alone, and seem to esteem them a great 
delicacy. They take short flights over the water in bright weather, 
from April to July, during the breeding season, and will leave 
their quarters during a drought, and fly to other waters at any 
time that they may be compelled to do so. 
They are very prolific, laying a number of small round whitish 
eggs, which in size and appearance somewhat resemble those of 
the mackerel. They may be found in numbers on the undersides 
of the floating leaves of aquatic plants, and also on pieces of wood, 
and on dead leaves in the water. On the whole, it is an insect 
that may rather be looked upon with favour, although it may kill 
off a few of the more weakly, or it may be sickly, fry when it gets 
a chance. It is useful as a scavenger, and as soon as the fry have 
grown a little they will not leave a corixa alive within their 
borders. 
When the fry have advanced so far that they can thoroughly 
master a corixa, they turn their attention to, and are large enough 
to take, a fresh water shrimp (Gammarus pulex), which is 
a crustacean of the sub-class Edriophalina. 
This is one of our very best friends, which should 
be introduced by all means into all trout waters, 
and cultivated assiduously. It may easily 
be distinguished by anyone, and in general 
appearance closely resembles the sand hoppers, 
so common on the sea-shore. It is a very 
prolific breeder, and retains its eggs until they 
are hatched. It is an excellent scavenger, and appears to be 
harmless, although slander says it likes fish eggs. It does not 
appear to do any harm to trout ova, for the experiment has now 
been repeatedly tried, by placing gammarz in the same tank with 
trout eggs. Although their movements have been carefully 
watched, they have not been detected doing any harm. They 
may hide under them if they get the chance, but, seeing that in 
natural waters trout eggs are buried in the gravel, such an 
occurrence is not likely to take place. In the hatching boxes, of 
course, they can do no harm, even if so disposed, for the simple 
reason that they are not allowed to enter. It is their nature to 
Fig. 27. 
Gammarus pulex. 
