Taxonomy & naming
Hydrophlox chrosomus was described by David Starr Jordan in 1877 as Alburnus chrosomus, from a tributary of the Etowah River near Rome, Georgia. It spent most of its history in Notropis, and stores still sell it as Notropis chrosomus. The Catalog of Fishes now places it in Hydrophlox, a genus split from Notropis for the redfin and rainbow shiner group. Use Hydrophlox chrosomus as the valid name.
Morphology
A slender, small-mouthed shiner. FishBase gives a maximum length of 3 in TL for males or unsexed fish. As the common name says, the species carries a rainbow of colour along the flank, which intensifies in breeding males.
Habitat
FishBase places the species in the Coosa, Cahaba, Alabama and extreme upper Black Warrior river systems, all part of the Mobile Bay drainage, in northwestern Georgia, Alabama and southeastern Tennessee. Adults live over gravelly riffles and pools, sometimes sandy pools, in creeks and small rivers, and are also found in springs and small clear streams. Whether the species migrates is undetermined. FishBase classes it as benthopelagic and temperate, with a latitude range of about 32 to 35 degrees north.
Feeding
FishBase does not list the diet of this species. Like other small stream shiners it takes small invertebrates from the water column and the stream bed.
Mating
Courtship and spawning behaviour are not recorded in the FishBase entry. Males show their strongest colours during the breeding season.
Breeding
Fecundity, egg type and spawning season are not recorded in the FishBase entry, and no captive breeding reports are known to the atlas.
In the aquarium
This is a cool-water native fish, seen mainly in native-fish and temperate tanks. Keep it in a long tank with strong flow, a gravel bed and clean, well-oxygenated water, in a group of at least six. FishBase gives no temperature, pH or hardness range for the species. It shares its range with darters and other Mobile Basin minnows, which make suitable tank mates. Cover the tank, as minnows jump.
Conservation
FishBase lists the rainbow shiner as Least Concern on the IUCN Red List, assessed 1 March 2012. It depends on clear, silt-free gravel streams, so sediment from land clearing is the main local concern for the Mobile Basin populations.