How to distinguish between rat and mouse in Chinese? I know there are two words here: 老鼠 and 鼠. However, the dictionary states that 老鼠 (rat) can also mean mouse; how do you specify rat?

I imagine that 仓鼠 (hamster) and 沙鼠 (gerbil) are often abbreviated to 鼠???

If so how does one specify that you mean mouse, rather than rat, hamster or gerbil?

P.s. maybe someone could also drop in a comment about whether or not these animals are common house pets in China / HK / TW?
Actually, in ordinary life, Chinese don't distinguish mice and rats(Frankly speaking, when I was a student, studying English and met the two words, I was also wondering why there are two words in English?). We just call that dirty animal that often appears in the houses "老鼠" or "耗子"(oral word,common in dialects).When we see a mouse(rat?) in a field, we may call it "田鼠"(田 means the field). 

仓鼠 is a kind of pet(one of my friends raise two). Wiki tells me rat is "大家鼠" and "mouse" is “小鼠", but I and people around me don't care this.

Of course, in scientific circle, academical researchers will adopt the Binomial Nomenclature(in Chinese, 二名法) system to distinguish them.