Among the Acanthopterygii, or the spiny-finned fishes of Cuvier's arrangement, the only one suited to the fresh-water tank, is the noble perch, Percidæ. These are bold and dignified, and their decisive markings make them attractive in a general collection. They require plenty of room, or they soon show signs of exhaustion; and, under the best of circumstances, cannot be pronounced a hardy fish in confinement. They are capricious. I have had healthy specimens, taken by net, die off in a week; and weakly ones, taken by the hook, with portions of the lower jaw torn away, recover, and live for a year, after the ragged portions had been removed by scissors.
Gasterosteus needs a word or two. The sticklebacks are all pretty and interesting fish, plentifully found on the sea-coast, and in brooks and ponds all over the country. The species most frequently met with are G. semiarmatus, the half-armed stickleback, and G. pungitius, the ten-spined, but G. brachycentrus (short-spined), and G. spinulosus (four-spined), are rare.
Aquarian amateurs seem a little divided about the policy of keeping these in tanks. I can only advise the beginner to be careful, or he may regret having made their acquaintance. They are all savages, untameable savages, that delight in destruction, even if they cannot eat what they destroy. They will attack anything, and, with their spiny armour, dare the stoutest to retaliate upon their mischief-making pertinacity. In fact, they pass all their time in worrying the more peaceful members of the aquarium; and any one who has a few months' experience of them, will consider them the savagest of imps.
I have tried them on several occasions, and found them at spawning time more savage than usual; but at all other times savage enough. My favourite Prussian carp, that love me as I love them, that come when I call them, that hurry to the side when I fillip the glass with my finger-nail, that watch me with all their eyes when I sit in the room with them, and that feed from my hand as a dog would, show at the tips of their pretty tails the sanguinary signs of gasterostean vengeance. Their transparent tails are ragged through the attacks of those sharp-toothed savages, and more than one has succumbed to their persevering spite since my recent trial of them under the persuasion of a little friend who begged me to put in some "robins" he had caught at the brook. "Robins," indeed, the red jaws of G. aculeatus are suggestive of his bloodthirsty propensities, and he now does penance with a dozen of his kindred in a glass jar of Callitriche autumnalis. With tench, gudgeons, and minnows they do better, but they are very annoying to carp of all kinds.
REPTILES, MOLLUSKS, AND INSECTS.
The lower orders of creation supply many interesting specimens for the aquarium. Among the reptiles—newts, or water lizards, and the common frog, may be recommended as offering some forms of positive elegance, and some habits worthy of observation. The smooth newt, the warty newt, and the noble triton, are almost essential to the completion of the collection, and as they respire air at the surface, they do not exhaust the water of oxygen. The beautiful markings on the belly, and the graceful motions of these strange creatures, are sure to afford entertainment to those who can overcome the very common repugnance felt towards such creatures.
Some of the mollusks commend themselves for their beauty, and will be prized by the aquarian enthusiast. Among the univalves, lymnea, physæ, planorbis, and paludina, are the most useful and ornamental. I must caution the amateur against the too ready adoption of any species of lymnea; they are destructive, and particularly fond of Vallisneria, Stratoides, and Callitriche, and while they are the best of cleaners, they are also the most indiscriminate of gluttons.