My aunt is going to give us a fish tank and I am going to buy fishes. Like cats and dogs they can't be kept in the house. So can fishes be kept in a house?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

It is permissible for you to put this tank inside the house, but if that causes an unpleasant smell, then it would be more appropriate to put it in a special place.

We remind you that you have to be kind to the fish, feed them according to their need, and clean the tank when needed. It is confirmed that the Prophet said: "A woman entered Hell-fire because she tied a cat, she did not feed it and did not set it loose so that it could eat small insects and small animals." [Al-Bukhari and Muslim]

It should be noted as well that it is not permissible to keep a dog except if it is used for guarding one's farm or cattle or for hunting as stated in the Sunnah.

Allaah Knows best.