阅读短文，根据短文内容及首字母提示，在空白处填入一个适当的单词。

Do you like animals? Do you want to keep animals? Yes, many people like animals and want to keep a lovely animal as a p_____ . It's a pity that they don't have a suitable place to keep them. However, keeping fish may be the best choice.

Why keep them?

People keep dogs and cats because they enjoy their friendship. Fish can not be friendly, but they have beautiful shapes and colors. It's a pleasure to watch as they swim i_____   their tank（水槽）。

What do they need?

First of all, the fish need a suitable （合适的） tank, and you must fill the tank w_____  suitable water. It is also good for t_____  to have a few water plants in the tank to keep the water pure （纯净）。 Putting a few snails （蜗牛） in the tank is a good i_____  . They will keep it c_____  

What about feeding them?

There are many kinds of fish food t_____   you can get in the shops. Most are suitable for all kinds of fish. You should feed your fish only o_____   a day. It is important not to give them  t_____   much food. Just give them as much as they can e_____   up in about 15 minutes. This will keep them healthy.