The Tennessee dace (''Chrosomus tennesseensis'') is a species of
ray-finned fish
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...
in the family
Cyprinidae
Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...
. It is found only in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
; particularly in northeast Tennessee and southwest Virginia, and parts of extreme northwest Georgia. Until recently, they were considered a subspecies of mountain redbelly dace. They are commonly found in East Tennessee in spring fed first-order streams, often in silt and fine gravel pools, or undercut banks.Hamed, K. 2008. Life History Traits of the Tennessee Dace (''Phoxinus tennesseensis'') in Northeast Tennessee. ''The American Midland Naturalist''. 160: 289–299. These streams usually do not exceed two meters in width.Etnier, D. 1993. ''Fishes of Tennessee''. 243–248.
Like all Tennessee species in the genus ''
Chrosomus
''Chrosomus'' is a genus of small cyprinid fish found in freshwater habitats in the eastern half of the United States and Canada. There are currently seven recognized species in this genus. They have sometimes been included in ''Phoxinus''. They ...
'', Tennessee dace have tiny scales and scaled breasts. They usually have scarlet bellies, and are considered one of the most beautiful native fish in Tennessee.
Tennessee dace are considered nest associate spawners, using central stoneroller (''
Campostoma anomalum
The central stoneroller (''Campostoma anomalum'') is a fish in the family Cyprinidae endemic to North America.
Biology
Stonerollers have a rounded snout overhanging a crescent-shaped mouth, a hard ridge of cartilage on the lower lip, and irr ...
'') and common creek chub (''
Semotilus atromaculatus
''Semotilus atromaculatus'', known as the creek chub or the common creek chub, is a small minnow, a freshwater fish found in the eastern US and Canada. Differing in size and color depending on origin of development, the creek chub can usually be ...
'') nests as spawning grounds. There is evidence to suggest that the Tennessee dace can interbreed with the common creek chub.Eisenhour, D. 1997. Two New Intergeneric Hybrids Involving ''Semotilus atromaculatus'' and the Genus ''Phoxinus'' with Analysis of Additional ''Semotilus atromaculatus'': ''Phoxinus'' Hybrids. American Society of Ichthyologists and Herpetologists. 1: 204–209. Spawning for Tennessee dace starts in April and extends into July. Both males and females gain even more coloration during the breeding season.
Their diet is similar to that of other dace species, consisting mainly of attached algal growth. Historically, Tennessee dace have only been found in 62 locations. Due to limited distribution and other factors, they are considered "in need of management" in Tennessee.Hamed, K. 2001. Distribution of the Tennessee dace, ''Phoxinus tennesseensis'', in northeast Tennessee. 80: 1–5. Future threats include human development and climate change.
Systematics and etymology
''Chrosomus tennesseensis'' is a member of the same monophyletic group that contains ''
Chrosomus cumberlandensis
The blackside dace (''Chrosomus cumberlandensis'') FishBase.) is a species of
Chrosomus oreas
The mountain redbelly dace (''Chrosomus oreas'') is a species of ray-finned fish in the genus ''Chrosomus''. It is found in mountain and Piedmont regions of the Atlantic slope of North America from the Shenandoah River in Virginia, to the Neuse ...
'' (mountain redbelly dace) and ''
Chrosomus saylori
The laurel dace (''Chrosomus saylori'') is a species of freshwater minnow native to the U.S. state of Tennessee. It was first discovered in 1976. A very rare species, it has only been found in localized populations in six small streams on the Wald ...
'' (laurel dace). Until recently, the Tennessee dace was thought to be a variant of the mountain redbelly dace. However, morphological characteristics distinguish the two similar species. The Tennessee dace has a break in the dark lateral stripe that runs down the side of the body. Also, the Tennessee dace's eye pupil diameter is larger than the diameter of the dark spots above the lateral stripe, while the spots of ''oreas'' are larger than the pupil. The ''oreas'' is a more robust minnow with fewer scales in the lateral series. The species name "''tennesseensis''" means "of Tennessee," which is a reference to the Tennessee River drainage encompassing much of its native range.
Description
The Tennessee dace has a complete lateral line. Their dorsal coloration ranges from nearly plain olivaceous to profusely speckled with black.
Nuptial
A wedding is a ceremony where two people are united in marriage. Wedding traditions and customs vary greatly between cultures, ethnic groups, religions, countries, and social classes. Most wedding ceremonies involve an exchange of marriage ...
males have red lower sides and bellies, with red scattered around the operculum, in the preorbital area, and at the base of the dorsal fin. The pectoral, pelvic, and anal fins are yellow, while the breast and lower head are black. Bright silver areas occur at the anterior base of the dorsal, pectoral and pelvic fins. Tennessee dace exhibit
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
. Males have more rounded pectoral fins while females have narrower and more pointed fins.
Geographical distribution
The Tennessee dace has an extremely limited distribution, as it is only found in eastern Tennessee, extreme southwestern Virginia, and northwest Georgia. As of 2008, there are only 62 known populations. Specifically, it occurs sporadically in small tributaries in the ridge and valley margins of the Blue Ridge and Cumberland Plateau provinces of the upper Tennessee drainage from Virginia southwestward. Watersheds include the Emory and lower Clinch river systems, and south to the
Hiwassee River
The Hiwassee River has its headwaters on the north slope of Rocky Mountain in Towns County in the northern area of the State of Georgia. It flows northward into North Carolina before turning westward into Tennessee, flowing into the Tennessee Riv ...
system. They were likely extirpated from Whiteside, which is just west of
Chattanooga
Chattanooga ( ) is a city in and the county seat of Hamilton County, Tennessee, United States. Located along the Tennessee River bordering Georgia, it also extends into Marion County on its western end. With a population of 181,099 in 2020, ...
.
Ecology
The Tennessee dace inhabits spring-fed, first order streams that are usually less than two meters in length and shaded by woody vegetation. Woody vegetation often includes hemlock and
rhododendron
''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are nati ...
species.Starnes L.B. and Starnes W.C. 1981. Biology of the Blackside Dace ''Phoxinus cumberlandensis''. ''American Midland Naturalist''. 106: 360-371 They prefer the ridge and valley limestone region. In stream habitat includes silt and fine gravel pools and undercut banks with woody debris and other material to serve as cover. Studies conducted found that root masses and other woody vegetation is critical for the survival of the Tennessee dace. Adults use root masses as cover, and young-of-the-year are often found inside of root masses. Debris that falls into streams provides additional cover.
Similar to other dace species, Tennessee dace feed on algal growth which is grazed from rocks and other debris on the stream bottom, and possibly beneath banks. While they are grazing
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, they coincidentally ingest tiny sand particles. These sand grains rupture diatoms and other algal cells during digestion. This is an important aid to digestion, as the cell walls of plants are difficult for the fish
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s to break down. Additional nutrition may be obtained from both root hairs and bacteria associated with algal growth, and immature insects, which are consumed in the winter when algae supply is limited.
Dipteran
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
and
caddis fly
The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...
larvae make up most of their insect diet.
Little research has been done on the Tennessee dace's natural predators, but both mammals and birds have been known to feed on them in shallow pools.
Behavior and life history
Tennessee dace spawn from April to July, and they have been found to spawn when water temperature is around 21 °C. They have the ability to spawn twice during this time period, but most only spawn once in their lifetime. As with other ''Phoxinus'' species, spawning occurs in the afternoon on clear days. The Tennessee dace has a law
fecundity
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...
rate compared to similar species. Ova produced by females ranges from 398 to 721. This is considerably less than mountain blackside dace, which can produce close to 3,000 ova.
Multiple male Tennessee dace have been observed following a single female through pool and run areas. In fact, as many as 20 have been observed following a single female. Males would form a straight line with the snout of one male just behind the caudal fin of the preceding male. They have also been observed leaping out of the water one hour before and after spawning.
Tennessee dace are nest associate spawners, meaning they use nests already made by other species to spawn. They have been found to use the nests of common creek chub and central stoneroller. If nests are not available, some ''Chrosomus'' species are thought to use shallow riffle areas in streams. Being a nest associate spawner has benefits, such as physical protection provided by the nest, and protection provided by the host of the nest. However, nest association may contribute to species rarity. Several minnow species that are nest associate spawners are protected on federal or state levels. Tennessee dace initiate spawning as soon as the nest is vacated by the host, allowing them to spawn. It has been hypothesized that a chemical cue from a nest building minnow may trigger ''Chrosomus'' species to spawn.Rakes, P.L. et al. 1999. Reproductive behavior, captive breeding, and restoration of endangered fishes. ''Environmental Biology of Fishes''. 55: 31-42.
Natural hybridization is relatively common among North American cyprinids, and this is the case of the Tennessee dace and the common creek chub. This hybridization likely occurs due to their similar breeding behaviors, such as communal use of gravel nests. Degradation of streams is thought to increase the chance of hybridization, as this leaves a lack of clean gravel substrates needed for spawning.
Conservation
The Tennessee dace is listed as G3 (globally vulnerable to extirpation) and S3 (state vulnerable to extirpation and extinction). It is listed as "in need of management" in Tennessee and "endangered" in Virginia.