Cady Gray's "Survive and Thrive" class at SLUFY made ecosystem aquariums out of cut-apart two-liter soda bottles and brought them home with minnow inside. It's an ingenious setup. The bottom section holds aquarium gravel and a water plant. The top section has the bottle-top "funnel" set in upside down, with a cloth filter fastened to the spout, filled with dirt and grass seed and covered by another soda-bottle-bottom "dome." As the grass grows, the roots poke through the filter and reach down to the aquarium's water, and moisture from the grass and soil, filled with nutrients, trickles down into the fish's habitat.
My girl has been reminding us frequently that she really wants a pet. So Minnie the Minnow (so CG named the fish) arrived in a timely fashion. And in the couple of weeks since SLUFY, the fish has thrived. We have a thick mat of grass in the upper dome, long roots reaching down into the water, and a fish that darts around in a way expressly calculated to delight a five-year-old.
I looked up the life cycle of the fathead minnow, and found to my surprise that it can live up to fourteen months. Uncertain that we want to try to maintain this soda-bottle contraption for a year, I talked to Cady Gray about releasing Minnie into a nearby stream before school starts. She was receptive to the idea. But of course I have mixed feelings. She does really want a pet, and letting this one go just means we have to think about a more permanent situation. (Maybe one of those bettas that lives in the roots of a phylodendron?) And is my real motivation to avoid the death-of-your-pet discussion with Cady Gray by sending her minnow into the wild before we find it floating belly up?