Abstract: A dual-purpose cap for a jar-aquarium comprising a topwall having (a) at least one ingress aperture sized to accept free unbroken water-stream passage therethrough for cap-on filling of the jar-aquarium and (b) at least one egress aperture smaller than the ingress aperture and spaced therefrom to facilitate controlled cap-on out-pouring of water, whereby jar-aquarium water may be changed without removing the cap. A series of egress apertures may be grouped together along the edge of the topwall.

Abstract: 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.

Abstract: A method for providing a nutrient-enriched aquarium waste-water for plant watering, comprising the steps of: adding a fresh clean water to an aquarium; determining a time point when the aquarium water becomes a waste-water deleterious to fish but rich in nutrients beneficial for plants; removing at least a portion of aquarium waste-water from the aquarium into a receptacle; and selling the aquarium waste-water as a plant fertilizer.

Abstract: A theme jar-aquarium including: a readily-portable container having a bottom wall, a surrounding sidewall, and an open upper end; a cap removably secured to the container and having a topwall with at least one aperture; and at least one theme element non-removably secured to the interior surface. Such theme element can be integrally formed with the container. In certain desired embodiments, an exterior theme element is secured to the outer surface of the jar-aquarium. Also desirable is an embodiment having an exterior handle secured to the sidewall.

Abstract: 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.

Abstract: A dual-purpose cap for a jar-aquarium comprising a topwall having (a) at least one ingress aperture sized to accept free unbroken water-stream passage therethrough for cap-on filling of the jar-aquarium and (b) at least one egress aperture smaller than the ingress aperture and spaced therefrom to facilitate controlled cap-on out-pouring of water, whereby jar-aquarium water may be changed without removing the cap. A series of egress apertures may be grouped together along the edge of the topwall.