What’s a wedge tank?

A wedge tank is a tank designed to keep adult fish away from their own offspring (to stop them eating them). Similar designs are found in breeding traps, where a sloping partition with a narrow slit at the bottom allow young fish to drop down and away from danger. Other options might be to use a rigid mesh as a divider — as long as the gaps are large enough for young fish to swim through, but too small for the adults to follow, it will work.