The ‘o’opu nōpili (Sicyopterus stimpsoni) is a species of fish endemic to the freshwater streams and estuaries of Hawaii. Also known as the Nopoli rockclimbing goby or Stimpson’s goby, the fish used to live in streams on all major Hawaiian islands, but today its distribution is reduced to a few areas. On the island of O’ahu, it is commonly found in unaltered streams such as the Kaluanui, the Kahana and the Waimea.
Both the male and female ‘o’opu nōpili vary in color according to age: Juveniles and females are mottled brown or gray, while males are often striped and have a pronounced dorsal fin. They do not exceed 20 centimeters (8 inches) in length.
O’opu nōpili have elaborate courtship rituals. Spawning takes place in crevices under rocks between August and March. The eggs, defended by the males, hatch within two to three days and the larvae head out to sea, spending about five months as ocean plankton. Once they have survived, they are called hinana. In the spring, they return to the estuaries for at least 48 hours before starting to migrate upstream. During this period, they undergo a physical and physiological change: They elongate, their heads increase in size and their mouths become adapted to scraping algae off rocks.
As well as once being common in local kitchens, wrapped in banana leaves before being cooked (pūlehu), ‘o’opu nōpili were also traditionally used in ceremonies like the mawaewae (weaning) ceremony for firstborn children, to ensure that blessings and good fortune would protect the child. They were also used in housewarming celebrations for good luck. The name ‘o’opu nōpili comes from the Hawaiian word for "cling," referring to the fish’s ability to climb waterfalls by clinging to rocks. The idea was that fortune would cling to the child’s life or the house, just as the ‘o’opu nōpili clings to rocks.
The ‘o’opu nōpil is, for many Kanaka Maoli families, an amakua, a protective deity of the family, often a deified ancestor, according to Hawaiian mythology.
It is currently threatened by overfishing, illegal harvesting and habitat degradation. Canalization and the diversion of watercourses to irrigate intensive sugar cane plantations, as well as introduced exotic species, pose a threat to the ‘o’opu nōpili.
Despite the declining population trend, various projects are underway to protect the species and its habitat. The objectives of conservation actions are not only to protect current populations, but also to boost numbers so as to protect the fish from future extinction. ‘O’opu nōpili can also be used as an indicator species, as its presence signifies high water quality in streams.