I keep getting these random fishes in my inventory. I have no clue where they came from and now I seem to have like 5 different fishes. is it an effect of having a hydrus pet or something?

Well, thay are coming from random events, you are just missing those. There are a lot of different fishes that you get randomly when browsing the site. It has nothing to do with your pets or anything, but with the current event.

oh ok..But i don't seem to get an event O_o I did get this one where it said something about high water and I got my first fish but then the other ones just appear :O