Many fish build nests of one type or another, but the small sticklebacks-most species are only a few inches in length-are probably the champions of them all.
The nests are built by the male from twigs, stems, leaves and similar rubbish, which, using his mouth, he fashions into a hollow structure with a single entrance, cementing the material with a sticky substance secreted by glands connected to the kidneys.
The nest when completed is a comparatively elaborate structure usually attached to reeds or some other suitable foundation. The stickleback then sallies forth in search of a wife whom, by persuasion, or even by such strong-arm methods as sticking her with his spines, he induces to enter the nest. Once inside, the female deposits the eggs and then breaks through the back wall of the nest and swims away. The males of some species are not satisfied with a single conquest but, after fertilizing the eggs, go out and repeat the whole process.
When sufficient eggs have been procured from females willing to be pilfered, the male guards the nest until the eggs are hatched and the young are old enough to shift for themselves.