Also, with the plastic breeder boxes, the water doesn't circulate properly and goes stale. The nets are far better as the water circulates through. I had the shock of my life when my swordtail gave birth, there were about 50 of the little blighters! A couple were dead and only their eyes were left as they rotted really quickly. I have to say that I let them out into the community to fend for themselves, they're not very good at surviving as they all got eaten. I wonder if it's because they're quite white, whereas the guppies are a bit more camouflaged when they're young.