In my first "mini" tank project (linked above) I designed a perfect nano tank for guppies which then introduced a crab. The crab then got its own tank which led to issues with leaking unfortunately. This all led me to go get a 12 litre glass aquarium as the male guppy had done his job and all 3 females where pregnant.
So I thought long and hard about the set-up instead of just dumping some gravel in with the fish and hoping for the best, this is generally a recipe for disaster. While planning my female crab killed the other crab in it's tank and this left my puzzled as they'd been getting on somewhat OK, that was until she dropped her tail hatch and showed me the hundreds of eggs she was carrying.. Yes the crab was also pregnant!
The glass tank is 30CM long (12") by 20CM deep and wide which for those who do not know works out like this:
A) Want to put the female guppies in a breeding net / tank
B) Leave the female guppies alone swimming free in the tank.
There are pros and cons to both options but option B of leaving them alone in my opinion best. Here's why:
Most guides will recommend you place the female guppy in a breeding box / net or separate tank just before she's due to birth. However this causes the fish a lot of stress as its suddenly placed in an environment much smaller than it was just swimming in.
The second reason why not is because you must be there to see her finish birthing to take the adult out so she doesn't eat her own fry all contained inside the same area. Although many breeding boxes have holes in the bottom to let the fry drop through if the female adult takes a long time to birth then the very first lot of fry will be active and swimming back up in with the parent. Overall it's less stress and more natural to leave the fish alone and let nature take its course.
That said there are things you can do to help the fry survive. First of all I have a large piece of coral rock in my tank which has pits, holes and tunnels that go through and inter-connect, around the back of the tank I have water grass types of plants that just break the water surface and provide lots of shelter for the fry to swim into. By well placing the grass I created a nursery area along the back of the tank where the fry can really swim about with protection from adult fish.
My orange female guppy was the first to birth, there are only 2 clips. The first was taken with a GoPro where the quality for being a Gopro was not good, the second with my SLR camera and was much better.
Meanwhile the crab was caring for her eggs and since the video was taken realised them all. I primitively placed a women's stocking over my filter to prevent eggs being sucked in, but it's still unlikely any will live as it is for most.
As I'm expecting some red cherry shrimp from a local friend I'm going to do a follow up with photos and video of the set-up and how the guppy fry are coming alone.