Unusual tail shape on guppy fry

[Joby]

Its one of the three 8 day old lucky fry that have survived in my largest tank. I noticed the last few days that its tail wasn't the same as the other two but assumed it was clamped because it was stressed at trying not to be dinner for the adult guppies.

I took a closer look today as they are getting more adventurous and coming out of the plants more and its tail is shaped like a spear doesn't look clamped at all now I can see it better and its bigger

Is this a common shape as I've never seen it before? The dad is unknown as the female along with others were given to us as a present and she was already pregnant

I'm hoping to try and catch these 3 when I water change tomorrow as they are coming out and about more.

 

[Tempestuousfury]

Could it be a spade tail?