Flagtail
The flagtails are a family of centrarchiform ray-finned fish of the Indo-Pacific area. The family consists of 13 species in one genus, Kuhlia. Most are euryhaline and often found in brackish water, but the genus also includes species restricted to marine or fresh water.
Several species are known as Hawaiian flagtails, particularly K. sandvicensis and K. xenura.
Etymology
The genus Kuhlia is named for the German zoologist Heinrich Kuhl.Description
The distinctive characteristic of these fish is a scaly sheath around the dorsal and anal fins. The dorsal fin is deeply notched between the 10 spines and the 9 to 13 soft rays. The opercle has two spines, and the anal fin three. Their bodies are compressed and silvery, and they tend to be small, growing to at most.During the day, they usually school, dispersing at night to feed on free-swimming fish and crustaceans.
A study of sperm motility in Kuhlia marginata found that sperm were most active in water with salinity between 25 and 35 parts per thousand, indicating that the species spawns in seawater rather than in rivers. This provided the first experimental evidence that K. marginata is catadromous, migrating from freshwater habitats to the sea to reproduce. Estimation of spawning sites in the spotted flagtail, Kuhlia marginata, based on sperm motility.
Analysis of otolith strontium-to-calcium ratios confirmed that Kuhlia marginata spends its early life stages at sea before migrating to freshwater, then returns to the ocean to spawn. The study also found that males typically die at sea after spawning, while females may return to rivers and spawn multiple times during their lifetime
In Hawai‘i, flagtails, known locally as āholehole, inhabit a wide range of environments, including marine, estuarine, and freshwater habitats. These fishes play an important ecological and cultural role in Hawaiian coastal systems. Some use them as a food source and cultural ceremonies.