Guppy fry with bent spine

One of my female guppies who was pregnant (I'm not a breeder, though) had gotten sick the other day, so I separated her in another tank. A few days later, she passed away while giving birth and only one little baby made it. He is 9 days old today. Unfortunately, I am noticing that his spine is curving upwards, like a V. I know that most of you would tell me to cull him so he doesn't pass what may be a bad gene, but I don't have the heart to do this to our little survivor.

I'm just wondering if it could be something in the water causing him to develop wrong or is it really genetics? His spine seemed fine at first, but it's pretty hard to tell because he was really tiny and see-through when born (probably born too early)
He is being fed crushed flakes about 3 times a day... he has about 7 hours of darkness at night and the temperature is 24C as I type this. He gets a 50% water change once a week.

Any ideas what could be causing this?

Hmm.. I hope it'll end up being a female, so it'll be easier to get rid of the babies. If it's a male, it'll be harder to tell if he was the one to get my females pregnant or not. I wouldn't want to get rid of perfectly fine little fry.

But mostly, I hope it's not genes and that he'll live a long happy life anyway.