I must begin by apologizing for "fishture"; not the greatest pun I've ever produced. I had considered some kind of not-so-bad but mightily obscure reference to the Mr. Sparkle episode of the Simpsons--something along the lines of "Tamaribuchi Fishbulb," but that would have required all kinds of potentially-copyrighted Simpsons art on this page to explain the connection. So "fishture" has won the day, so far.
Right, so, this is a fairly common round glass cover which attaches to a light fixture and acts as a shield to protect the light bulb inside and/or as a diffuser to help, ah, diffuse the light which comes through it. Thus they come in unfrosted and frosted varieties, depending on whether you think insufficient diffusion is a problem, or perhaps would prefer not to have to look at the ugly lightbulb you know is lurking inside the frosted bowl. Mine was of the frosted type, but the frosting was easily removed by filling the bowl with 50 vol% pool acid/water and letting it soak overnight, leaving (after some dumping, light scrubbing, and washing-out) nice clear glass like a goldfish bowl.
The fake fish, fake plant, and rocks were gutted from an almost-empty bottle of Liquid Habitats Hand Soap I'd asked for last Christmas and was about to throw away. After washing the soap off everything and drying carefully, the base of the plant was epoxied to a small, flat rock, and the lower extreme tail of the fish was epoxied to a heavier rock. These figures were arranged in a pleasant little undersea diorama inside the globe, the remaining rocks were poured in to stabilize everything, and the whole was submerged in about a liter of USP mineral oil, which boils somewhere around 280 degrees centigrade (~500 degrees Farenheit) which I considered to be safely above temperatures likely to be generated by a light bulb. Still, to be on the safe side (and more practically because a larger bulb would've actually dipped into the oil), I downgraded to a fairly wimply 7.5W "sign" bulb of the type used in my fractal chandeliers. You can leave one of these bulbs on all night, get up in the morning and rest your palm on the glass with no discomfort.
The mineral oil is a bit messy. Much the same effect could have been achieved by setting up the diorama in the bowl and then casting the whole thing in polyester resin, which looks very much like water (as long as it doesn't turn yellow) and has the advantage of not sloshing around.