# Hawaiian freshwater goby

The Hawaiian freshwater goby, or ʻOʻopu (Lentipes concolor) is a species of goby endemic to Hawaii, commonly located in freshwater mountain streams in higher elevations.

## Geographic Distribution / Habitat

Located in upper regions of perennial streams on the Hawaiian islands of Hawaiʻi, Maui, Molokai, Kauai, and Oahu, Lentipes concolor possess the ability to scale waterfalls during their migration back into fresh water . L. Concolor inhabits the widest variety of stream types, occupying streams of up to 750m elevation and is well adapted to a range of conditions including floods and extended drought. Although the Lentipes Concolour has been listed as a Category One endangered species candidate, there have been reports of rising populations in recent years.

## Anatomy

Males of the L. concolor have been found to reach a length of 7 cm (2.8 in), while females only reach 6 cm (2.4 in). The species' body color tends to be grayish and olive-brown with darker irregular lateral spots that appear like dorsolateral bands. Although both sexes lack coloration in the anterior regions, males possess a yellow to bright red posterior trunk; a sex-based variation that has been linked to immersion in formalin or naturally occurring formaldehyde in water. Females have sometimes been found to show small black spots along the dorsal midline. Another prevalent sex distinguishing feature would be the spacing of dorsal fins. In males, the second dorsal fin is positioned closer to the first dorsal than it is in the female. Additionally, the morphology of the skull has been found to have size differences between males and females in the median notch of the upper lip and in head length relative to lengths of the pectoral fin and body. L. concolor possesses small and scattered cycloid scales limited to the posterior half of the trunk. Males of the species generally comprise fewer total scales (2-120) than do females (20-150). Compared to scales in juveniles, scales are thin, often embedded, sometimes degenerate, and decrease in number with increasing body length and maturity (MACIOLEK, J. A. 1978).
These fish utilize the "powerburst" mechanism, where fish push off against surfaces with their pectoral fins and propel upwards reattaching to the surface with pelvic suction. The fish pushes forward with the pectoral fins while detaching the pelvic disk and rapidly undulating the body from side to side. This mechanism allows L. concolor to climb faster and reach further upstream compared to the Awaous Guamensis and other freshwater fish found in Hawaii.
The species are able to climb these heights, in part, as a result of its herbivory. This might give it an ability to feed and restore muscle energy by consuming algae (diatoms are algae) on the surfaces of the falls as it climbs.

## Life History

The Hawaiian goby are amphidromous and have lengthy marine larval phases that facilitate dispersal. Amphidromy is a type of a life cycle that consists of spending time split between freshwater and marine environments. Upon emerging from laid eggs, larvae drift downstream to their oceanic feeding sites and become a part of the pelagic zooplankton community until they mature into post larvae. Once reaching maturity to the post-larvae stage they migrate back into fresh water which is where they metamorphose rapidly into juveniles.
L. concolor is notable for its unusual method of returning to the spawning beds (something they however share with a few other gobies, including another Hawaiian species, Sicyopterus stimpsoni); they use suction disks on their ventral sides to climb the wet rocks behind waterfalls, even scaling the 442 ft-high (135 m) Akaka Falls.
Interestingly, studies have shown that downstream movement of larvae occur more commonly during new-moon phases. Disruptions in spawning behaviors of Lentipes Concolor have been linked to the lack of lunar periodicity in upper streams which lead to higher frequencies and intensity of flash floods.

## Diet

L. concolor have been found to consume a greater proportion of plant materials with up to 93.1% dry biomass and 6.5% animal material. Lentipes Concolor are omnivorous and utilize suction feeding, as they possess a jaw skeleton with a lever system suited for fast jaw opening.
L.Concolor have been found to consume green algae and a range of insect larvae that are captured by suction feeding when these larvae are washed into streams. In many streams, the most common food items are the larvae of chironomid flies who lay their eggs on rocks near the water line. These fish also "frequently dart up from the bottom and intercept particles carried downstream in a manner reminiscent of the sallying behavior of insectivorous birds that fly up from a perch and capture insect prey. It has not been determined to what extent the omnivorous fishes are actually digesting plant material rather than receiving nutrition from the periphyton (aufwuchs) attached to it.".

## Decline in Native Oʻopu populations

Lentipes concolor has been listed as a Category One endangered species candidate. This species has become a management priority for the State of Hawaiʻi and federal agencies, with research on the biology being initiated in 1973.
The 3 major threats to Lentipes Concolor include, in-stream habitat degradation, exotic species introductions, and the loss of "ridge-to-reef" migratory corridors due to the disruption of surface water connectivity.
Water use for humans including extraction and diversions substantially alter the distribution through the reduced availability of in-stream habitat and by disrupting surface water connectivity. The disruption of surface water connectivity reduces or eliminates freshwater flow into coastal marine environments. Additionally, urbanization leads to the elimination of riparian vegetation, channelization and streambed stabilizations that result in shallow, straight, concrete-lined channels.This alteration in the environment intended for flood control has reduced habitats for feeding, predator avoidance, and reproduction for native fishes. Furthermore, marine larvae are directly reduced due to the effects of urbanization and coastal developments that result in heavy metals, chlorinated hydrocarbons, petrochemicals, nutrients and bacteria contamination.
Climate change is expected to negatively affect rainfall and cloudwater deposition,which are both key atmospheric sources of water that support surface flow in oceanic island streams. In addition, climate change leads to ocean acidification and the increase in temperatures will enhance energy demands for metabolism.
The introduction of Invasive species alters native communities through increased predation and competition over the availability of nutrients. Introduced game fish such as largemouth and smallmouth bass have been identified as predators on post-larvae and adults that reduce ʻoʻopu populations.

## Cultural and Historical Significance

This species is important to the native people as a food fish. In Ancient Hawaii, this species, and others such as mullet and Kuhlia sandvicensis, were cultivated in a form of freshwater aquaponics or aquatic polyculture. In this system of farming, the taro in the upland paddies (taro being the primary staple in Ancient Hawaii) was aided by the fish such as the Hawaiʻian freshwater goby, through these fish pruning the leaves and eating the pests, thus leading to a symbiotic system of food production.