the bottom the glass can be quickly cleaned with the aid of water and fine sand, or rotten-stone.
Exhaustion of Oxygen is made manifest by the fishes coming to the surface to gulp air, and it is also manifested by their retiring to the bottom, and quietly extending themselves on their backs in “horizontal repose”—the repose of death. If too many animals be crowded into the vessel, this will soon happen, and either the number must be reduced or the water must be frequently changed, or we must have recourse to aeration. I consider the two latter remedies a proof of the incompetency of the aquarian—the necessity marks very bad management indeed.
Temperature.—If the aquarium be too much exposed to the heat of the sun in summer, or to the heat of a fierce fire in winter, the water will get tepid, and signals of distress will be shown by the protrusion of many panting mouths at the surface. I find that if the temperature rises above sixty degrees, things do not go on so well. The use of a blind or paper screen is, therefore, essential in summer time.
On winter evenings, when the room is made cozy by blazing blocks of coal, the collection will often show signs of distress. By opening the lower window-sash one or two inches when leaving the room for the night, things may be restored to a normal state in a few hours, and even if the weather is somewhat severe no harm will be done. At the same time intense cold checks the growth of the plants, and throws the fishes into a state of torpor, and the freezing of the water may cause the bursting of the tank.
