The three-spined stickleback is covered with metallic hued bone plates on both sides, and its dorsal and ventral fins are sharp spines. During the spawning period in June to July, the red-bellied males conquer a territory near the bottom and build a nest using pieces of aquatic vegetation. They bravely protect their offspring with the three dorsal spines upright. In Finland the three-spined sticklebacks only live a few years. The three-spined stickleback is very wide-spread on the Northern hemisphere – it is known in the Mediterranean, the Black Sea, as well as the Californian and Japanese coasts. Three-spined stickleback is a very fatty fish. In the first half of the 20th century three-spined stickleback was used to boil fish oil, which was used for example in lamps. In spite of the spines, three-spined stickleback is an important part of diet for salmon and trout.