Picture by Chad Thomas, Texas State University-San Marcos
Rio San Marcos at San Marcos (Jordan and Gilbert 1886).
Etymology/Derivation of Scientific Name
Macr – Greek, meaning “long”, referring to elongated forms of Hybopsis (Scharpf 2005); marconis refers to San Marcos, the type locality for this species; the common name, burrhead chub, refers to the diagnostic head tubercles of nuptial males (Eisenhour 2004).
Eisenhour (1999) recognized Macrhybopsis marconis as a distinct species within the M. aestivalis complex. See Eisenhour (1997) for complete synonymy.
Hybopsis aestivalis marconis Jordan and Gilbert 1886:315-316; Davis and Miller (1967).
Hybopsis aestivalis aestivalis Hubbs et al. (1953).
Macrhybopsis marconis Eisenhour (1997, 1999, 2004); Hubbs et al. 2008:21.
Maximum size: 73 mm (2.87 in) TL (Eisenhour 2004).
Coloration: Lateral stripe distinct along side of body (Hubbs et al. 2008). Eisenhour (2004) described coloration: live specimens are somewhat translucent, pale olive dorsally and silvery-white ventrally with broad silver lateral stripe; small melanophores on posterior dorsolateral scales concentrated to form submarginal band on scales appearing as vague diamond pattern. Preserved specimens with dark and continuous lateral stripe present from operculum to caudal peduncle, centered on lateral line and one scale wide, this feature obscured in live specimens by the silvery coloration. All dorsal rays outlined with pigment, and first 6-8 pectoral rays pigmented; pelvic and anal fins with little or no pigment. Lemon-yellow pectoral fins in nuptial males (Eisenhour 2004).
Counts: Pharyngeal teeth 0,4-4,0; 19 (17-20) caudal fin soft rays; 8 (7-9) anal fin soft rays; 8 (8-9) pelvic fin soft rays; 13-15 (12-16) pectoral fin soft rays; 35-38 (35-39) lateral line scales; 0-20 predorsal scales; 5 (4-6) scales above lateral line; 4-5 (4-6) scales below lateral line; 12 (11-15) caudal peduncle scales; 13-16 (11-17) infraorbital pores; 11-13 (9-14) preoperculomandibular pores; 36-38 total vertebrae; 17-18 (17-19) precaudal vertebrae; 18-19 (17-20) caudal vertebrae (Eisenhour 2004).
Specimens from the Colorado River drainage on average have fewer lateral-line scales than specimens from the Guadalupe-San Antonio River drainage (36 vs. 37), and fewer predorsal scales on average than specimens from the Guadalupe-San Antonio River drainage (9 vs.15) (Eisenhour 2004).
Body shape: Terete with deep, long caudal peduncle; eye large, round or almost so (orbit depth >80% of orbit length); snout rounded.
Mouth position: Horizontal and inferior (Eisenhour 2004); gape width not as wide as head when viewed ventrally; lips only slightly fleshy.
Morphology: Nape fully scaled; belly posterior to pelvic bases fully scaled; usually with bridge of scales on belly just anterior to pelvic fin bases, occasionally with only few scales or naked; dorsal and anal fins bluntly pointed; pelvic fins rounded; pectoral fins rounded or bluntly pointed and short, not reaching origin of pelvic fins in adults; one pair of maxillary barbels present, usually < 45% of orbit length [Blanco River specimens with longer barbels (48-63% of orbit length) than specimens from remainder of range (25-50% of orbit length)]; small taste buds present as small papillae on gular region; in both female and male, genital papillae absent or poorly developed as small conical flap; gill rakers absent or present as 1-4 dorsal rudiments (Eisenhour 2004). Pectoral rays 2-8 to 2-10 thickened in nuptial males and bear rows of conical, slightly antrorse uniserial tubercles on dorsal surface; tubercles also present on the head of nuptial males, most concentrated anterior and ventral to eye and dorsum of head with the cornified portion of these tubercles a narrow cone that rests upon a round, fleshy base; in large males (in peak nuptial condition) smaller tubercles present on predorsal surface of body; females lack tubercles; females >50 mm SL with slightly thickened pectoral rays; on females, cephalic taste buds enlarged, but not cornified (Eisenhour 2004).
Distribution (Native and Introduced)
U.S. distribution: Found only in Texas.
Texas distribution: Occurs in the San Antonio and Guadalupe rivers; remnant populations may exist in the Edwards Plateau portion of the Colorado River (Eisenhour 2004; Hubbs et al. 2008).
Abundance/Conservation status (Federal, State, Non-governmental organizations)
Special Concern (Hubbs et al. 2008). Common to abundant in the Guadalupe and San Antonio drainages; population in the Colorado River drainage has declined (Eisenhour 2004).
Macrohabitat: Large streams (Eisenhour 2004).
Mesohabitat: Occupies flowing water over coarse sand and fine gravel substrates in medium to large streams; found to be most abundant in riffles over large gravel and cobble (Eisenhour 2004).
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
Eisenhour (2004) found Macrhybopsis marconis to be sympatric with the shoal chub (M. hyostoma) in the middle Colorado River mainstem (Burnett, Travis and Bastrop counties). Eisenhour (2004) found that M. marconis specimens had shorter barbels than M. hyostoma; also, specimens of M. hyostoma from the Brazos and Colorado River drainages had lower mean indices of belly squamation (1.03 and 0.31, respectively) than specimens of M. marconis from Colorado River drainage (3.33) and fewer mean preoperculomandibular pores than specimens of M. marconis (10.59-11.37 vs. 12.17). Macrhybopsis marconis may further distinguished from M. hyostoma by a well-defined lateral stripe continuous from the operculum to the base of the caudal fin approximately one scale wide and having tubercles on the head of nuptial males (Eisenhour 2004).
No information at this time.
Commercial or Environmental Importance
No information at this time.
Davis, B.J., and R.J. Miller. 1967. Brain patterns in minnows of the genus Hybopsis in relation to feeding habits. Copeia 1967(1):1-39.
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. 1999. Systematics of Macrhypbopsis tetranema (Cypriniformes: Cyprinidae). Copeia 1999: 969-980.
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.A. Kuehne, and J.C. Ball. 1953. The fishes of the upper Guadalupe River. The Texas Journal of Science 5(2):216-244.
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, 2nd edition 43(4):1-87.
Jordan, D.S., and C.H. Gilbert. 1886. List of fishes collected in Arkansas, Indian territory, and Texas, in September, 1884, with notes and descriptions. Proc. U.S. Nat. Mus. 9:1-25.
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.