The five native freshwater fish of Hawai‘i are referred to as ‘o‘opu. Scientifically, they are actually two distinct families. The family Gobiidae (Goby – one of the largest fish families in the world) includes four species of ʻoʻopu, the nakea, naniha, nōpili and ‘alamo‘o. The ʻoʻopu ‘akupa is in the Eleotridae family. (Wascher)
All species of Hawaiian ʻoʻopu begin their life in the streams. Newly hatched larvae are swept out into the ocean, where they continue development.
After about six months in the ocean ʻoʻopu nōpili, now called “hinana” (together with the larvae of the other four freshwater fish species,) return to the streams. (Schoenfuss)
Different ʻoʻopu are found in different parts of the stream; the distribution is mainly influenced by the climbing ability of each species. (Schoenfuss)
Many gobies can inch their way up waterfalls with the aid of a sucker on their bellies formed from fused pelvic fins. The Nōpili rock-climbing goby, on the other hand, can climb waterfalls as tall as 330-feet with the aid of a second mouth sucker.
“For a human to go the equivalent distance based on body size, it’d be like doing a marathon, some 26 miles long, except climbing up a vertical cliff-face against rushing water.” (Researcher Richard Blob; Choi; LiveScience)
Spawning occurs between August and March and eggs are deposited in crevices under rocks and pebbles. Nests are laid in territories defended by males. Eggs hatch within two to three days and larvae are washed out to sea as oceanic plankton.
Post-larvae can be found in schools just after recruitment. After recruitment ʻoʻopu nōpili remain in estuaries for at least 48 hours before they begin migrating upstream.
While in the estuaries of the stream, this change in head structures occurs rapidly (within 36 hours) and enables the fish to continue its migration upstream. (Schoenfuss)
During this time, they undergo a significant metamorphosis. Their snouts enlarge and lengthen and their heads increase in size.
Their upper lip also enlarges and their mouths move to a sub-terminal position. (DLNR)
Their pelvic fins are fused together to form a suction cup which helps them fasten to rocks, the stream bottom, and even to climb waterfalls. (NTBG) This metamorphosis allows the ʻoʻopu nōpili to climb waterfalls using its suction cup and lips. (DLNR)
Most other gobies feed on small invertebrates or other fish, but the Nōpili rock-climbing goby prefers to scrape tiny bits of algae, called diatoms, off rocks using a mouth-sucking motion mirroring the same movements it uses to climb walls.
Researchers report that they found that the nōpili rock-climbing goby’s climbing and feeding movements differed significantly. In other words, the fish are using different movements for feeding and for climbing. (Smithsonian)
Video of ʻoʻopu nōpili summary (Schoenfuss)
The goby, which can grow up to 7 inches long as an adult, feeds by cyclically sticking the tip of its upper jaw against rock to scrape food off surfaces. This behavior is quite distinct from other Hawaiian gobies, which feed by sucking in food from the water. (Choi; LiveScience)
There is a visible difference between males and females. When not engaged in courtship behavior, males resemble females, having a yellow-green, brown, or gray base mottled with brown or black. During courtship, however, the male’s body darkens and it develops an iridescent “racing” stripe down its sides. (Sim; PBRC)
Besides being a favorite food fish, ‘O‘opu Nōpili was also used ceremonially. The name of this ‘O‘opu comes from the Hawaiian word for cling (pili). It refers to the fish’s ability to climb up waterfalls by clinging to rocks.
It was used in the mawaewae (weaning) ceremony for first-born children, so that blessings and luck would cling to the child. It was also used in house-warming feasts, with the intent that good luck would cling to the house. (Sim, PBRC)
‘Oʻopu nōpili have been used as an “indicator species” to signify high water quality in streams and the possible presence of ʻoʻopu ‘alamo‘o, which is rarer than the ʻoʻopu nōpili. (DLNR)
Video of ʻoʻopu nōpili at waterfall (Spanish language narration)
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Cole C. Adams says
They don’t spawn in the ocean AND THEN mature in the rivers, so they are not catadromous (like Anguila). Nor do they spawn in the rivers AND THEN mature in the ocean; thus, they are not anadromous (like Salmonids). So what are they considered?