For a setup like a 45-gallon Rubbermaid tub, you don’t actually need anything too heavy-duty—just steady surface agitation or a small air stone is usually enough for gambusia.
A simple and cheap option is a
battery-powered aquarium air pump (the kind anglers use for live bait buckets). They usually run on D-cells or even AA batteries and push enough air for an airstone in a small volume like yours. Some also have auto-switch backup in case power drops, which is handy.
→ The key thing is oxygen exchange, not “circulation” like a big pond. As long as you’ve got bubbles breaking the surface, you’re good.
Another decent route is a
portable USB air pump paired with a power bank. These are surprisingly reliable for small setups and can run for hours depending on battery size.
→ For winter, just keep in mind: aeration helps, but it won’t fully stop freezing in exposed conditions. You may still need to partially insulate the tub or float something on the surface if temps drop hard.
If you want the simplest “set it and forget it” approach, a small bait aerator + a sponge filter is honestly one of the more practical
Best Pond Aerators-style solutions for a setup this size.
→ Gambusia are tough fish, so you’re more about preventing stagnation than creating strong flow.
Overall, keep it simple: air stone + battery pump is usually more than enough for a 45-gallon breeding tub.