CHAPTER IX
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.
LARVA OF DYTISCUS AND YOUNG TROUT.
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 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 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.