guppy longevity in isolated gene pool

[Aydreean]

that title sounded like a journal title o_o

Anyway, being just a little curious I thought that I'd ask this. My sister has a guppy tank and the majority of the guppies are second generation. I know they are going to in-breed and I was curious to see if there are any problems the third or fourth generation fish might have besides the lack of color. I keep urging her to just get a couple more males to keep the fish looking good.

[Sarkazmo]

Interbreeding is not catastrophic. All the breeds man's created have come from selective inbreeding for specific traits. With Betta it's typical to breed Father to Daughter(s) and even Father to Grand Daughter to get the colours and traits concentrated. The only problem is that you're compounding all traits, good AND bad. If the fish your sis has are strong, low in genetic problems then it's likely that they'll be just fine and produce beautiful offspring. A wider gene pool is always preferable when breeding for hardiness. This is why mutts tend to be very healthy dogs because they have a wide gene pool.

Sark