orst enemies of both ova and fry is the _Dytiscus
marginalis_, whether this insect be in the larval or adult stage. I
think that I should hardly be wrong in going even further and saying
that _D. marginalis_ is very dangerous to trout early in their yearling
stage. The accompanying illustration shows a larva of _Dytiscus_
which has caught a young trout. This illustration is taken from a
photograph of a specimen lent to me by Mr. F. M. Halford, and both the
fish and the larva were alive when they were caught. Unfortunately the
trout is a little shrivelled, and the legs of the _Dytiscus_ have been
broken. _D. marginalis_ lays its eggs in the stems of rushes. The larva,
when hatched, makes its way out, and proceeds to lead a predatory life.
The larva when full-grown is about two inches long, and is quite the
most rapacious creature which lives in our waters. The adult beetle is
also purely carnivorous, but is perhaps not quite so rapacious. It
would, however, probably attack a larger fish.

The largest of English water beetles is _Hydrophilus piceus_. This
beetle is not, in the adult stage at least, carnivorous, but the larva,
which is about half an inch longer and considerably fatter than that of
_D. marginalis_, is carnivorous. It may be told from the larva of
_Dytiscus_ not only by its size, which is hardly a reliable point for
discrimination, but by the smaller size of the head in comparison to the
rest of the body. The claws, with which _Hydrophilus_ seizes its prey,
are, too, considerably smaller than those of _Dytiscus_. This larva
should be kept out of the rearing ponds with just as much care as that
of the more voracious _D. marginalis_.

With the kingfisher I have already dealt at some length, so that I need
say but little more with regard to it. One of the worst features in this
bird's character is that it will go on killing many more little fish
than it can possibly eat. As I have before said, it is surprising how
these birds will appear in considerable numbers where a fish hatchery is
started, even in localities where they have before been considered rare.
I have already described how the ponds should be protected from their
ravages.

Herons do a great deal of harm to fish ponds, even when the fish have
got well into the yearling stage. I have on one or two occasions known
of herons wounding trout of at least a pound in weight. Besides the
actual damage they do by killing fish, they put all the other fish in