What’s the difference between mammals and fish?
There are a few differences between mammals and fish. Firstly, the important traits of mammals are that they don’t lay eggs. Most mammals give birth to their babies. Secondly, mammals are warm-blooded. Thirdly, mammals have fur and hair. In my opinion, these are main differences between mammals and fish..

这个题目蛮怪的，mammal属于animal，
Mammals give birth to their babies and feed them with milk.
Animal is a big family including fish, reptile, insect, mammal, bird and so on.
正在上班，水平有限，先写两句。回家问问小子，这种话题是他最擅长的。.