It don't really think it is. My ducks eggs that are fertile have a much larger more noticable bullseye.
My chickens have layed eggs that had a HUGE bullseye in them but there is no way they were fertile since I don't have a roo. That is what most of my chickens eggs look like.
I'm gonna say no, not a fertile bulls eye. It is the female egg cell, but it does not look fertilized to me. There is a thread, by Speckledhen (i think) that shows some great pics of the difference. A fertile egg will have a white dot, then a tiny area around that dot that is lighter in color, then another ring of white around that space, hence the name 'bullseye'. It can be hard, hard, hard to spot the difference, and its easy to mistake- I'm sure I've been wrong lots of times, but after youve seen a few really obvious examples, you start to kinda get an eye for it.
So, why are you asking???
ETA- I went back and looked harder at the picture, and it actually looks possibly fertile. I'm still leaning towards no, but, like I said- I've been wrong lots of times!!
The reason why I was asking is because I thought it was a bullseye myself... Thing is I only have 2 adult female ducks right now. My drake is only 4 weeks old. He's been spending time with them, but he's still a little skittish of the adult ducks.
I thought maybe my call was a hermaphrodite. lol
But I did see the post with the really good bullseye pics, and I don't think it is.