224 IDEAL HOME LIFE
problem: (1) The tank may be placed in better light to encourage plant growth; (2) a larger supply of vegetable food may be introduced so that the tadpoles may have sufficient after the more active fishes have taken their share. In this case any surplus not consumed should be removed after a few hours; (3) the tadpoles may be removed to another receptacle occasionally and fed separately. However, a careful study of the conditions of the aquarium should make this latter method unnecessary.
Although tadpoles are vegetarian in their diet, the young frogs and toads after their metamorphosis are strictly carnivorous, and are adapted to a flesh diet only. They may be fed on insects, earthworms, mealworms, grubs, or pieces of fresh meat cut to a suitable size. Just at the time of change when the horny jaws of the tadpoles are being shed to allow the development of the teeth, they will take no food. This period of change extends from a few days to several weeks, according to the species and the temperature of the water.
Crayfishes and crabs are naturally scavengers and will eat almost anything. They prefer a meat diet, however, and if deprived of this they are very likely to turn cannibal and eat each other.
Cleaning the Aquarium
It must be clearly borne in mind that cleanliness is absolutely necessary to the welfare of the inhabitants of the aquarium. In an aquarium which is properly set up contamination can arise only by bacterial decay of organic substances allowed to remain in the water. There are three general sources of such organic matter: first, fecal matter from the animals, relatively unimportant because the deposits are small in amount and regular in occurrence; second, decaying vegetable matter from dead portions of the plants, also relatively unimportant since in the well-balanced aquarium there is little tendency for the death of the plant tissues; and third, decay of excess food matter, the usual source of pollution.
If care is taken in feeding—and a little study and experience in this matter is the only safe guide—no appreciable