Trout The Friends And Enemies Of The Fish Culturist
The creatures which are sometimes found in and around rearing ponds
containing ova or young fish are very numerous, and it is advisable that
the fish culturist should have some knowledge of them. It is for this
reason, that while I cautioned my readers against the creatures which
are dangerous, and enumerated some of those most serviceable as food, I
left detailed descriptions of these enemies and friends of the little
fish, in order that I might deal with them in a separate chapter.
Among the worst 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
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
the pond off their feed through frightening them. After a heron or
kingfisher has been about a rearing pond the little fish will not feed
for a considerable time, sometimes even for days. Notwithstanding their
very evil proclivities, both herons and kingfishers are very
interesting. A kingfisher, if he catches a fish which is a little too
big for him to swallow whole, will knock the head of the fish, which he
always catches by the middle of the body, against a stone, in order to
kill it, or at least to stop it struggling; it might otherwise in its
struggles escape, as the kingfisher can only swallow a fish head first.
There are stories which tell how herons sometimes pluck small feathers
from their breasts and, floating these feathers upon the water, catch
the trout as they rise to it; it is supposed that the trout takes the
feather for a fly. Personally, I do not think that much credence should
be attached to the latter story.
Other birds, usually found on or near the water, are also likely to do
much harm to the ova and young fish. Almost every creature which is
found near the water seems to have a great liking for the ova of fishes.
All the wading and swimming birds are to be dreaded by the fish
culturist. They will, all of them, eat ova in enormous quantities, and
many of them will also eat the little fish.
Besides birds, small larvae of several insects will eat, or at any rate
kill, the ova in considerable numbers. Caddis-worms are among these
larvae which eat ova. This seems to be one of the few cases in which
nature is just, for caddis-worms are taken very readily by even small
trout. Large trout will take them very greedily, cases and all.
Therefore, I should advise the fish culturist to cultivate them as food
for the fish he is rearing, but to be very careful that they do not get
into the rearing boxes or hatching trays when he has ova in them. The
caddis-worms kill the ova by making a small hole in them and sucking
some of the contents out; from this hole some more of the contents
escapes, and as it comes into contact with the water becomes opaque.
Caddis-worms are the larvae of an order of four-winged flies commonly
known as sedges, caddis-flies, or water-moths. The latter appellation is
of course a misnomer, as these flies (_Trichoptera_) have nothing
whatever to do with moths. They resemble moths, however, in that they
have four wings which when at rest lie in much the same position as do
those of moths, and as many of them have their wings thickly covered
with hairs, this resemblance is sometimes very marked. The larvae
(caddis-worms), being eagerly sought as food by many fish, and having
very soft bodies, make for themselves cases. Some of these cases are
made from small sticks, some from little pieces of stone or sand, and
some from a mixture of all of these substances. As these cases resemble
such small pieces of rubbish as are frequently found in streams, care
should be taken that they do not get into the hatching trays containing
Many of the water beetles, and practically all of their larvae, will
attack the ova; they should therefore be carefully excluded from the
hatching trays. As there are about 114 different species of beetles in
the family of _Dytiscidae_ alone, my readers will appreciate my reason
for not attempting to enumerate them. It will be a sufficient warning to
state the fact that they are all carnivorous, and their relative sizes
is the only thing which will decide whether the beetle will eat the
fish, or the fish the beetle.
Very similar to beetles are some of the water-bugs. They may, however,
easily be distinguished from beetles, as the outer or anterior wings of
the bugs cross each other at their lower ends, while the elytra of
beetles, which much resemble the horny, anterior wings of some of the
water-bugs, meet exactly in the middle line. These water-bugs, though
some of them are excellent food for even the small fish, will attack the
ova, and therefore they should be kept out of the hatching trays. The
fish culturist should, however, whenever it is possible, cultivate such
of these water-bugs as are good food for the fry in separate ponds, as I
have before recommended. The best of these water-bugs are _Corixae_.
Others, such as the water-boatman, water-scorpions and pond-skaters, are
not of any value as food for the fish.
The larvae of _Ephemeridae_ are very good food for the fish, and should be
cultivated in separate ponds if possible, and some turned into the ponds
containing the little fish occasionally. A fair proportion should,
however, be kept in the ponds and protected, so that a good stock of the
flies may be available next year.
The larvae of _Ephemeridae_ may be obtained in many streams, and are best
caught with a fine gauze net. Some of them swim, but most are generally
captured with such a net at the bottom of the water among the _debris_.
Eggs of _Ephemeridae_ may be obtained sometimes from another locality if
they cannot be got on the spot. These should be carefully preserved for
the first year at any rate, and a good fly may thus be introduced into a
water where it was before unknown.
I have already spoken of the fresh-water shrimp and the water-flea
(_Daphnia pulex_). These valuable articles of diet should be introduced
whenever it is possible. _Daphnia_ must be reared in a stagnant pond,
the fresh-water shrimp (_Gammarus pulex_) in running water, with plenty
Other useful creatures besides those snails and mussels which I
described in a previous chapter, are the water-louse (_Asellus
aquaticus_), _Cypridae_, and _Cyclops quadricornis_. Asellus is very
similar in size and shape to the common garden-louse, which is found in
decaying wood. It will live either in stagnant or running water.
_Cypridae_ are very much smaller, being generally only as large as a
large pin's head. They have a bivalve shell which makes them look
something like a small mussel. They are, however, very active, swimming
by means of two pairs of legs. They also possess two pairs of antennae
and one eye. (The species belonging to the genus _Candona_ of the family
_Cypridae_, do not swim.) _Cyclops_ is another very small crustacean,
shaped like a large-headed club. It swims very actively, and, like the
_Cypridae_, is an excellent article of diet for very young fish. Both
these crustacea live in stagnant water, and must, therefore, be kept in
a separate pond, whence they may be taken as required to be given to the