Translation:You also eat fish.
I thought 也 also can mean "both". Am I mixing it up with another sign, or am I correct here?
You might be mixing it up with another character. I don't think I've encountered a usage of 也 like that. If I said something like "我的妹妹和我也吃鱼。", that would be in English, "My little sister and I also eat fish." There usually is context before using 也.
For instance, if I went to a party with my little sister and we're talking to someone about our diets (a weird premise, but follow me here). A人：我不喜欢肉，可是我吃鱼。 我：我的家人是差不多吃素的，可是我的妹妹和我也吃鱼。
So it the exchange is something like:
A: I do not like eating meat, but I eat fish. Me: My family is more or less vegetarian, but my little sister and I also eat fish.
Pinyin: Ni ye chi yu You eat fish too Will be a better translation Just sayin u know Btw i am 11