Hiya Jelly, right order but the sea stickleback gets to 23 cm., this one gets to 3 cm. and is strictly fresh water.
They do look alot alike though, (here is a pic) of the S. spinachia.
I knew I knew that fish! It is the Burbot, (Lota lota).
Check out post #113 in this thread, I used the same picture to answer one of the Trust's posts!