Three-spined stickleback

Threespine sticklebacks spawn in freshwater. During breeding season, mature males will migrate inland, as far as 93 miles upriver, to set up territories and create nests. They will usually dig a tunnel or pit a few inches long, using their mouth. They then bring in nesting materials such as bits of plant. They often add red bits of material, too. The male glues his nest together using a sticky secretion called spiggin that is produced by his kidneys. The entire nest building process can take up to 4 hours. The male will do a courtship dance for a female, zigzagging around his nest and showing her the entrance, enticing her to lay her eggs inside. After she lays her 50-200 eggs, he chases her off. He might have multiple females lay their eggs in his nest before he fertilizes them. The male then spends 1-3 weeks tending to the eggs. He guards them from other tubenose poachers and potential predators and also fans them using his pectoral fins, to ensure that they are getting enough oxygen-rich water. By the end of the breeding season, he may have raised a total of 20 batches of eggs. For marine populations, the adults usually die after spawning. At hatching, young are 0.2 inches long. The young remain in the nest and the father will continue to guard them for up to 2 weeks after hatching. They reach a maximum length of 4 inches and can live to 3.5 years, though the maximum age varies with different locations.