For a vessel containing
twelve gallons the following selection of live stock is among those
recommended: Three Gold Carp, three Prussian Carp, two Perch, four
large Loach, a dozen Minnows, six Bleak, and two dozen Planorbis. Some
varieties of the Water-Beetles, or Water-Spiders, which the fishes
do not eat, may also well be added. The Newt, too, is attractive and
harmless.
All may go on well, and the water remain clear; but after the tank has
been established several weeks, the inner sides of the glass will show a
green tinge, which soon increases and interferes with the view. This is
owing to the growth of a minute confervoid vegetation, which must be
kept down. For this purpose the Snail is the natural remedy, being the
ready scavenger of all such nuisances. Snails cling to the sides, and
clean away and consume all this vegetable growth. The _Lymnea_ is among
the most efficient, but unfortunately is destructive, by eating holes
in the young fronds of the larger plants, and thus injuring their
appearance. To this objection some other varieties of snail are not
open. The _Paludina_ and _Planorbis_ are the only kinds which are
trustworthy. The former is a handsome snail, with a bronze-tinted,
globular shell; the latter has a spiral form.
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