Near San Antonio, Texas (Vaillant and Bocourt 1883).
Etymology/Derivation of Scientific Name
Micropterus = small fin; treculii = after discoverer of the species (Tomelleri and Eberle 1990).
According to Guillory (1980), Micropterus treculii was misidentified or placed in synonymy of other Micropterus species or subspecies until recognized as distinct subspecies of M. punctulatus by Hubbs and Bailey (1942). Species was elevated to specific status by Jurgens and Hubbs (1953) and Hubbs (1954). The following information from Garrett (1991):
Micropterus floridanus – Cope 1880:31-32. locality = Johnson Fork of Llano River, TX.
Dioplites Treculi – Vaillant and Bocourt 1883:Plate 4, Figure 2, original indication by figure, locality = San Antonio de Bexar, TX.
Micropterus nuecensis var. Treculii – Vaillant and Bocourt 1883:142, original text description.
Micropterus salmoides – Jordan and Gilbert 1886:21, locality = Rio Colorado, TX; Evermann and Kandall 1894:113, locality = San Marcos River, TX.
Micropterus pseudaplites – Hubbs 1927:15, localities = Rio San Marcos and Rio Colorado, TX.
Micropterus punctulatus puntulatus – Hubbs and Bailey 1940:15-16, 21, redescription of Dioplites Treculii.
Micropterus punctulatus treculii – Hubbs and Bailey 1942:1-11, localities = Guadalupe River, San Marcos River and Colorado River, TX.
Micropterus treculi – Jurgens and Hubbs 1953:14; Hubbs 1954:286, localities = Leon River, Cowhouse Creek, Berry Creek, San Marcos River, Guadalupe River, TX.
Maximum size: Largest known specimen was captured in Lake Travis in 1983, and holds the Texas state record at approximately 380 mm SL (Edwards 1997).
Coloration: 10-12 dark bars on side (darkest in young; Page and Burr 1991). Small spots on scales extend to near dorsal; dark lateral stripe obscured by barring; caudal spot usually indistinct (more so in adults); maximum depth of bars on body contained one and one-half to two times in maximum body depth (Hubbs et al. 1991). Fish inhabiting the Perdernales River, TX, have a more yellowish background coloration than those from other areas in the state (Edwards 1980).
Counts: 12 dorsal fin soft rays; 22-28 scales around caudle peduncle; 7-10 scales above lateral line; 14-19 scales below lateral line; more than 55 lateral line scales; 3 anal spines (rarely 2 or 4); 6-13 dorsal fin spines; 6 or 7 brachiostegals (Hubbs et al 1991).
Body shape: Moderately compressed, elongate body; large mouth (Page and Burr 1991); body depth usually contained three to five times in standard length (Hubbs et al. 1991).
External morphology: Shortest dorsal fin spine contained 1.1 to 2.5 times in longest dorsal spine; bases of soft dorsal and anal fins scaled; scales ctenoid (Hubbs et al 1991).
Internal morphology: Pyloric caecae not branched (Hubbs et al. 1991); glossohyal teeth present on tongue (Edwards 1980).
Distribution (Native and Introduced)
Texas distribution: Endemic to the streams of the northern and eastern Edwards Plateau including portions of the Brazos, Colorado, Guadalupe, and San Antonio basins; species also found outside of the Edwards Plateau streams in decreased abundance, primarily in the lower Colorado River; two introduced populations have been established in the Nueces River system (Hubbs et al 1991). Warren et al. (2000) list the following drainage units for distribution of Micropterus treculii in the state: Brazos River, Colorado River, San Antonio Bay (including minor coastal drainages west of mouth of Colorado River to mouth of Nueces River), Nueces River. Littrell et al. (2007) reported an apparent decline in the frequency of pure Micropterus treculii in the Blanco River, over the past 10 years; no pure M. treculii specimens were collected from the Blanco River during this study;
Abundance/Conservation status (Federal, State, NGO)
Species listed as vulnerable in southern drainages (Warren et al. 2000). Species listed as one of Special Concern, in Texas (Hubbs et al. 1991).
Macrohabitat: Streams and reservoirs; absent from extreme headwaters (Robbins and MacCrimmon 1974; Hurst et al. 1975; Guillory 1980; Tomelleri and Eberle 1990).
Mesohabitat: Species prefers for small lentic environments; commonly taken in flowing water; numerous smaller fish occur in rapids, many times near eddies; large individuals found mainly in riffle tail races; species inhabits smaller streams on the coastal plain; usually found in spring-fed streams having clear water and relatively consistent temperatures of 10-30 degrees C (Hurst et al. 1975). Species is moderately tolerant of high turbidity and variable temperatures (Guillory 1980). Abundant in turbid downstream sections of rivers, usually in gravel riffles, and at heads of deep pools which often have a silt substrate (Hubbs et al. 1953; Robbins and MacCrimmon 1974). Species prefers flowing waters of streams within native range, and uses large rocks, cypress knees, stumps and similar types of cover for refugia (Edwards 1980; Garrett 1991; Edwards 1997). Usually found in waters with annual thermal fluctuations of 4-35 C, but are absent in upper spring-runs with relatively constant water temperatures or below reservoirs with hypolimnion releases such as Canyon Reservoir (Edwards 1978, 1980; Garrett 1991; Edwards 1997). Salinity tolerance ranged from 14.4-18.4 ‰ (mean salinity at death 16.68 ‰; Edwards 1980). Tomasso and Carmichael (1986) found Micropterus treculii to be somewhat less resistant to ammonia than the majority of warmwater species tested, more resistant to nitrite than all noncentrarchids tested, and as resistant as other centrarchids; further, nitrate, at reasonable concentrations, appeared to have no toxic effect on this species. In streams occupied by both M. salmoides (largemouth bass) and M. treculii, M. salmoides will be found in the quieter areas, as M. treculii prefers running water (Hubbs et al. 1953; Hurst et al. 1975; Edwards 1980). In areas of Texas where both M. treculii and M. punctulatus (spotted bass) are found, M. treculii seems to prefer smaller streams while M. punctulatus prefer larger streams
(Hurst et al. 1975).
Spawning season: Nesting from early March through May or June (Hurst et al 1975; Boyer et al. 1977; Edwards 1980; Garrett 1991; Edwards 1997), with an apparent secondary spawning period in the late summer and fall (Edwards 1980; Edwards 1997). Hurst et al. (1975) reported spawning in the spring; likely May and June based on data gained from individuals in the Texas Natural History Collection showing that all fish less than 50 mm SL were collected in June, July or August, with each month having one or more fish less than 35 mm SL, and the presence of large ova in a 70 mm SL female collected in May.
Spawning location: In relatively slow moving pool areas close to a source of current in water greater than one meter in depth (Edwards 1997).
Reproductive strategy: Males tend to build nests near a source of slow to moderately moving water (Edwards 1980).
Fecundity: Edwards (1980) found fecundity to be positively related with female length: In the Llano River, egg numbers ranged from 399-2,009 in females measuring 128-167 mm SL; in the Guadalupe River, egg numbers ranged from 1,014-7,587 in females measuring 140-278 mm SL; and in the Lyndon B. Johnson Reservoir, egg numbers ranged from 3,199-9,286 in females measuring 177-242 mm SL (Garrett 1991). Significant variation in ova sizes found among different populations of Guadalupe bass, with females from the Guadalupe River basin having larger eggs (mean = 2.17 mm diameter, range = 1.85 to 2.25 mm diameter) than females from the Colorado River basin (mean = 1.63 diameter, range = 1.5 to 1.81 mm diameter) (Edwards 1980; Edwards 1997). Boyer (1977) reported similar sizes of ova from one M. treculi nest from a Guadalupe River site (mean = 2.058 mm diameter).
Age/size at maturation: 1 year old for both males and females (Edwards 1980). Smallest mature females collected measured 70 mm SL (Hurst et al. 1975), and 128 mm SL (Edwards 1980).
Migration: After leaving the nest the young move into gradually faster and deeper moving waters during their first summer and fall, often inhabiting the swiftly moving areas above and below riffles and in moving pools. Following spawning, adults return to the deeper, moving pool environments. Young-of-the-year fish move into deeper pool habitats with relatively constant moderate currents, during the winter (Edwards 1997).
Longevity: 6 years; oldest fish collected were females (Edwards 1980; Edwards 1997).
Food habits: Aquatic invertebrates found in stomachs examined; aquatic insects appear to be the main food item (Hurst et al. 1975). Main food of young fish was larval emphemeropterans (mayflies), other important diet items include fishes, aquatic dipteran larvae and terrestrial hymenopterans (bees and wasps); fish apparently increase taxonomic variety of diet items until reaching 60-90 mm SL, at which point the diversity of food items decreases (Edwards 1980, Garrett 1991; Edwards 1997). Seasonal variation of food items is greatest during the warmer months and least during winter; adults feed mostly on larval megalopterans (hellgrammites), crayfish, insects and fishes which are selected in proportion to the abundances in which they are found (Hurst et al. 1975; Edwards 1980; Tomelleri and Eberle 1990; Garrett 1991; Edwards 1997).
Growth and Population structure: In natural riverine habitat, growth is slow; in November, young of the year range from 58-111 mm; by the following July, that sample is 84-118 mm; 1-year-old fish attain a length of 150 mm by the end of the summer; 2-year-old fish are 150-200 mm long, and those larger have three annuli (Hurst et al 1975). According to Edwards (1980; 1997) fish reach lengths averaging 65-84 mm SL after one year, 121-154 mm SL after two years, 136-189 mm SL after 3 years and grows about 30 mm per year afterwards; data indicates males have lower mortality than females early in life, but females lived longer after age 3 (Garrett 1991). Fish in reservoir populations appear to become significantly larger than similar aged fish inhabiting streams (Edwards 1997).
Phylogeny and morphologically similar fishes
Micropterus treculii most closely related to M. punctulatus (spotted bass), and was commonly referred to as the Texas spotted bass (Tomerelli and Eberle 1990); these two species differ in that M. treculii has 10-12 dark bars along side (darkest in young; Page and Burr 1991). Markings and color pattern of M. treculii and M. dolomieu (smallmouth bass) are similar and may confuse attempts at identification, but the former species can be separated from the latter based on lateral line scale count (average of 65 in M. treculii and generally greater than 70 in M. dolomieu), and on the number of soft dorsal fin rays (generally 12 in M. treculii and 13 or 14 in M. dolomieu; Tomerelli and Eberle 1990). Similarity in spawning sites with those of the introduced smallmouth bass (M. dolomieu), has resulted in mass introgressive hybridization, especially throughout the Guadalupe River basin (Edwards 1979; Garrett 1988; Whitmore and Butler 1982; Whitmore 1983; Morizot et al. 1991; Edwards 1997).
Edwards (1980) reported the external parasites Uvulifer ambloplites (black grubs) and Lernaea spp. (anchor worms), and the internal parasitic nematode Contracaecum. Acolpenteron ureteroecetes (Monogenea), a worm found in the urinary bladder and ureter (Bunkley-Williams and Williams 1994).
Commercial or Environmental Importance
Micropterus treculii is the official state fish of Texas (Hubbs et al. 1991). Although small in size (a fish measuring 250 mm long would be considered “trophy” sized), M. treculii considered to be a worthy sport fish due to their occurrence in clear water habitats and a tendency to jump when on the hook (Hurst et al. 1975). There appears to be competition between M. treculii and the introduced species M. dolomieu (smallmouth bass), in areas where the two are found together (Hurst et al. 1975); coexistence of these two species is unlikely (Garrett 1991). Important factors contributing to the continued survival of this species are the preservation of high quality stream habitat and water quality (Hurst et al. 1975; Edwards 1980). Interspecific hybridization and introgression pose serious threats to the genetic integrity of M. treculii (Edwards 1979; Edwards 1980; Littrell et al. 2007).
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