A view to the truth here.
Inbreeding does not cause genetic problems but it will allow poor genetics to continue in a population and will allow bad recessive genes to be reinforced more often. The aristocracy in Europe is the textbook classic example of poor genetics being reinforced.
If you actively breed fish and select them to eliminate any defectives that show up, inbreeding will improve the line, not cause it to degenerate. It is a rather harsh approach since it requires intervention to prevent breeding of defectives but it has led to the present quality of domestic livestock that are almost always the result of line breeding (breeding an animal back to related animals on purpose).
Poor quality fish in pet shops are mainly the result of shipping stresses. When a shop replaces most of its stock every week or two, you are almost always looking at recent arrivals at the LFS. My own club had a LFS owner come and speak to us on some of the economics involved in his shop. One thing that came out was that he expected any new shipment of fish to have about a 10% loss rate in the first 3 days. For him it was something he had to account for in pricing fish if they were coming from very far. The fish are brought together at a shipper from many farms and placed into a single shipment of several bags of over 100 fish per bag. That adds to the time involved in shipping since an order must first be assembled somewhere. You start with a few days to build up a shipment, while some fish are sitting in bags, then add a day or two to arrive in the destination country and whatever time it takes to clear customs. Finally deliver the shipment to the LFS by way of a courier or other mechanism. Those pretty fish you are picking out of a tank at the LFS are probably still recovering from over a week in a shipping bag. They are not genetically weak, they are tough as nails or they would already be dead. If you do as I have and toss a mixed sex group into a tank to breed, you will have some robust young fish, even if you never add to the genetic pool. I sell off all of my adult guppies at each club auction and just let the fry grow out for the next auction. I add new blood to my colony when I see something I like at a club auction and bring it home. It just gets tossed into the mix and I continue to have great fish to sell at the auctions.
Another truth.
A 2 month old guppy should no longer be so small that you would worry about it carrying fry to term. If it is that small, try feeding more often and doing lots of water changes on the grow out tank. At 2 months it should look like a small adult that has yet to develop full colors and finnage.
But i dont want my females getting pregnant. They are a little more than two months old. When will my females be sexually mature? When can I expect to be able to get a general idea of the male/female ratio?
Are there any health risks to them being pregnant at this age?
