Near Western Union Office, Autopiste
There is a small strip shopping center, on the Puerto Plata - Sosua main & only road, I forget the name; just east of the baseball stadium rotary & almost, but not quite, directly across from the Shell gas station. The POP Western Union office is the largest tenant; every DR knows where that is!
There is a medium sized pet store; they carry a large product line for horses & dogs. Fish? I don't know but the owner - a Dominican-York - speaks nearly perfect English. He should be able to guide you.
Hint: don't viisit between 12:00 & 2:00; the usual story. Good fortune.