A multi-chamber selective-exposure aquarium apparatus including: a first portion forming a first aquarium chamber having a first transparent primary wall; a second portion forming a second aquarium chamber having a second transparent primary wall; and a visual barrier device for selective exposure/non-exposure of the first and second transparent primary walls, whereby fish in each of the first and second aquarium chambers are selectively visually exposed/non-exposed to each other's presence. Fish in separate aquarium chambers are preferably male betta fish.