Meaning of 増える in this sentence

Question

In the following sentence:

魚は三匹に増えていた。

I don't know whether to interpret に as to or by. So if I start with one fish then:

The number of fish increased to three (there are now three fish), or

The number of fish increased by three (there are now four fish)

Which is the correct translation and how would I modify the sentence to make it have the other meaning? Thanks.

Answer 1

It is the total number. I.e. now there are 3 fish.

To get the other meaning, you can say 魚が三匹増えた。