Question

There are some fish in the river . (一般疑问句加肯定回答)

Answer 1

Are there any fish in the river? Yes, there are(some).
fish作鱼肉讲是不可数名词，而作鱼讲则是单复同形的可数名词。
some一般用于肯定句，否定句、疑问句中中转换为any；但当说话者希望得到对方肯定回答时some疑问句用some。

Answer 2

Is there any fish in the river?
Yes, there is.

若有疑问及时追问，满意敬请采纳，O(∩_∩)O谢谢~~

Answer 3

疑问句：Are there any fish in the river?
肯定回答：Yes,there are.