You can tell this is a male ready to become a dad because of his blue color and the red-orange color under his throat. Its only during the summer breeding season that he will look like this. Not all males will color up this brightly as it depends on a number of factors including the amount of light and the surrounding environment (gravel color).
Think fish behavior is boring? Not a chance - BBC2’s springwatch featured two stickleback dads.
Watch the high drama trailer.