Picture by Chad Thomas, Texas State University-San Marcos

Macrhybopsis aestivalis

speckled chub

Type Locality

Rio San Juan at Cadereita, Nuevo Leon, Mexico (Girard 1856).

Etymology/Derivation of Scientific Name

Macr – Greek, meaning “long”, referring to elongated forms of Hybopsis; aestivalis – pertaining to summer, probably referring to its long spawning season (Scharpf 2005). The common name, speckled chub, is in reference to the prominent black body spots (Eisenhour 2004).

Synonymy

Gobio aestivalis Girard 1856:189.

Ceratichthys sterletus

Extrarius aestivalis sterletus Hubbs 1940:5.

Extrarius aestivalis aestivalis Sublette et al. (1990):86, 116-120.

Extrarius aestivalis

Hybopsis aestivalis Hubbs et al. (1977); Edwards and Contreras-Balderas (1991).

See Eisenhour (1997) for complete synonymy.

Characters

Maximum size: 90 mm (3.54 in) TL ( Eisenhour 2004).

Coloration: Most specimens with clusters of melanophores concentrated on single scales; other small melanophores randomly scattered over dorsolateral surface of body, not concentrated on margins or submargins of scales; dorsal fin soft rays  weakly outlined with pigment, the pigment darkest basally on first three rays; pectoral fin soft rays with some pigment on rays 1-7 or absent (Eisenhour 2004). 20-50 scales above lateral line with clusters of melanophores (Eisenhour 2004; Hubbs et al. 2008).

Counts: Pharyngeal teeth 4-4; fewer than 10 dorsal fin soft rays (Eisenhour 2004; Hubbs et al. 2008). 19 (16-21) principal caudal fin soft rays; 8 (7-9) anal fin soft rays; 8 (6-9) pelvic fin soft rays; 14-16 (11-18) pectoral fin soft rays; 34-38 (31-42) lateral-line scales; 0-19 predorsal scales; 4-5 (4-6) scales above lateral line; 4-5 (3-6) scales below lateral line; 12-14 (12-18) caudal peduncle scales; 13-17 (10-19) infraorbital pores; 10-13 (9-17) preoperculomandibular pores; 35-37 (34-38) total vertebrae; 17-19 (16-19) precaudal vertebrae; 17-19 (16-19) caudal vertebrae (Eisenhour 2004).

Mouth position: Horizontal and inferior (Eisenhour 2004).

Body shape: Terete and often robust anteriorly (Eisenhour 2004); snout rounded and blunt; lips moderately fleshy.

Morphology: One pair of maxillary barbels present, variable in length (usually < orbit length); taste buds enlarged into barbel-like papillae on the gular region; genital papillae absent or poorly developed as small conical flap; anus near base of anal fin; gill rakers absent or present as 1-4 dorsal rudiments; nape and belly fully scaled to naked (Eisenhour 2004). Pectoral rays 2-8 to 2-10 greatly thickened in nuptial males, with conical, slightly antrorse curved uniserial tubercles; nuptial males in peak breeding condition with minute tubercles on dorsal, anal, and pelvic rays; on nuptial males, cephalic and predorsal sensory papillae more pronounced, but not cornified into tubercles; females lack tubercles, although some large specimens (> 55 mm, 2.17 in, SL) with slightly thickened pectoral rays (Eisenhour 2004). Distance from anal fin origin to end of caudal peduncle goes 2.5 or fewer times in distance from tip of snout to anal fin origin (Hubbs et al. 2008).  Lateral line usually not decurved, either straight or with a broad arch; premaxillaries protractile; upper lip separated from skin of snout by a deep groove continuous across the midline (Hubbs et al. 2008).

Distribution (Native and Introduced)

U.S. distribution: Endemic to streams of the Rio Grande and Rio San Fernando (Eisenhour 2004; Hubbs et al. 2008).

Texas distribution: Found primarily in the Rio Grande between the confluence with the Rio Conchos and the Pecos River (Hubbs et al. 2008).

Abundance/Conservation status (Federal, State, NGO)

Special Concern (Hubbs et al. 2008). Species listed as Threatened in Mexico (Scharpf 2005) and Rare in Nuevo Leon (Eisenhour 2004). Common in most of the Pecos River and Rio Grande mainstem between the mouths of the Rio Conchos and Pecos River (Hubbs 1940, Hubbs et al. 1977; Sublette et al. 1990; Eisenhour 2004). The species has apparently declined in the lower Rio Grande mainstem as a consequence of reservoirs, channelization, and reduced stream flows resulting from irrigation withdrawal (Edwards and Contreras-Balderas 1991; Eisenhour 2004). Last collected in the upper Rio Grande in 1964; however collections from 1930-1950 suggest the M. aestivalis was common in this area prior to extensive changes in the Rio Grande (Eisenhour 2004). According to Sublette et al. (1990), it is extirpated in the upper Rio Grande mainstem.

Habitat Associations

Macrohabitat: Medium to large streams (Eisenhour 2004).

Mesohabitat: Flowing water over coarse sand and fine gravel substrates in streams; typically found in raceways and runs (Eisenhour 2004).

Biology

Spawning season: No information at this time.

Spawning habitat: No information at this time.

Spawning Behavior: No information at this time. 

Fecundity:  No information at this time. 

Age at maturation:  No information at this time.

Migration: No information at this time.

Growth and Population structure:  No information at this time.

Longevity: No information at this time.

Food habits: No information at this time.

Phylogeny and morphologically similar fishes

Macrhybopsis aestivalis distinguished from all other members of the M. aestivalis complex, the burrhead chub (M. marconis), the prairie chub (M. australis), the shoal chub (M. hyostoma) and the peppered chub (M. tetranema) in the fact it is the only one of the five chubs to reside in the Rio Grande drainage.

Host Records

 No information at this time.

Commercial or Environmental Importance

No information at this time.

References

Edwards, R.J., and S. Contreras-Balderas. 1991. Historical changes in the ichthyofauna of the lower Rio Grande (Rio Bravo del Norte), Texas and Mexico. The Southwestern Naturalist 36(2):201-212.

Eisenhour, D.J. 1997. Systematics, variation and speciation of the Macrhybopsis aestivalis complex (Cypriniformes: Cyprinidae) west of the Mississippi River. Unpubl. PhD Dissertation. Southern Illinois Univ., Carbondale. 260 pp.

Eisenhour, D. J. 2004. Systematics, variation, and speciation of the Macrhybopsis aestivalis complex west of the Mississippi River. Bulletin Alabama Museum of Natural History 23:9-48.

Hubbs, C., R.J. Edwards, and G.P. Garrett. 2008. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement, 2^nd edition 43(4):1-87.

Hubbs, C., R.R. Miller, R.J. Edwards, K.W. Thompson, E. Marsh, G.P. Garrett, G.L. Powell, D.J. Morris, and R.W. Zerr. 1977. Fishes inhabiting the Rio Grande, Texas and Mexico, between El Paso and the Pecos confluence. pp 91-97 In: Symposium on importance, preservation, and management of riparian habitat, Tucson, Arizona.

Hubbs, C.L. 1940. Fishes from the Big Bend region of Texas. Transactions of the Texas Academy of Science 23:3-12.

Girard, C.F. 1856. Researches upon the Cyprinoid fishes inhabiting the fresh waters of the United States of America, west of the Mississippi Valley, from specimens in the Museum of the Smithsonian Institution. Proceedings of the Academy of Natural Sciences of Philadelphia 8(5):165-213.

Scharpf, C. 2005. Annotated checklist of North American freshwater fishes, including subspecies and undescribed forms, Part 1: Petromyzontidae through Cyprinidae. American Currents, Special Publication 31(4):1-44.

Sublette, J.E., M.D. Hatch, and M. Sublette. 1990. The Fishes of New Mexico. University of New Mexico Press, Albuquerque. 393 pp.