The Sea Stickleback (Spinachia spinachia), which is also sometimes called the fifteen-spined stickleback (because it characteristically has between 14-17 dorsal spines).
Adults generally live solitary or in pairs, in shallow coastal areas and feed on small invertebrates. This fish can reach up to 25cm in length and is commonly found.
But here is the interesting part, male Sea Sticklebacks build nests (from bits of algae) using kidney secretions as glue to hold it all together. The females then deposit between 150-200 eggs into the nest and die soon thereafter, leaving the males to care for and guard their offspring. Sounds like a tragic love story doesn’t it?
We found this guy in the Kattegat, in Denmark during our Baltic expedition.
On a side note, can you spot the snails in the background?