If you snorkel in the Lagoon, or peer into its shallows, you are likely to see small schools of tiny fish. These are three-spined stickleback, fish that are unusual in just about every way.
Stickleback are unusual in design; are small (3 to 4 cm) slender fish with three prominent spines along their backs. These spines give the fish its name and can be locked upright in position, a defense against a predator trying to swallow it.
Stickleback are at home both in salt and freshwater; this is a rare feat for fish. This feature allows stickleback to swim back and forth between the Lagoon and the ocean. Stickleback can feed in both the Lagoon and the nearby Bay, but return to the Lagoon during the spring breeding season.
What makes stickleback most unusual is their breeding behavior. The male will stake out an area of the Lagoon, protect it from other males, and then construct a nest in a shallow depression. The males collect small bits of debris, glue them together with a secretion, building a tunnel-like nest.
The male then attracts the attention of a female, enticing her to enter the nest and lay eggs. After he has fertilized the eggs, the female is shooed away. The male guards the nest until the eggs hatch, and then continues to guard the young fry. All in all, quite extraordinary.