Specimens of H. g. gulonella that have been examined reach sexual maturity at approximately 65 mm standard length. Most specimens of H. g. gracilis less than 85 mm in standard length are immature, but larger specimens probably are mature.
The spawning season is in late summer, beginning in July and extending into September. Specimens from the Peace River, collected on August 10, 1952, include females that were mostly spent and tuberculate males. Males and females in spawning condition were collected in the Milk River in August of 1955. A large prespawning female was obtained in Red Deer River in June of 1952. A male from Fort McMurray had fairly well developed tubercles on August 9, 1955. A prespawning female was taken from the Saskatchewan River at Clarkboro Ferry on June 7, 1957. Tuberculate males were collected in the Powder River on June 30, 1957. Specimens from the White River in South Dakota, collected on July 7, 1934, include tuberculate males. The specimens discussed above are H. g. gracilis or intergrades tending toward that subspecies.
Specimens of H. g. gulonella collected in the Arkansas River at Pueblo and Florence, Colorado, on September 7, 1959, include some tuberculate males, although most females are spent. On August 8, 1957, a series of flathead chubs that includes tuberculate males was collected in the Redwater River, Montana. In the Pecos River on August 25, 1958, spawning seemingly had been completed, although a few males still bore tubercles.
Table 1. Organisms Found in Stomachs of Hybopsis gracilis From Various Locations, Expressed as Percentage of Total Volume.
| S. Saskatchewan R., Clarkboro Ferry, Sask. | B: Milk R., Alberta | Missouri R., S. D. | Missouri R., Neb. | Arkansas R., Fremont Co., Colo. | Arkansas R., Pueblo Co., Colo. | Pecos R., San Miguel Co., N. M. | |
|---|---|---|---|---|---|---|---|
| No. specimens examined | 1 | 7 | 6 | 10 | 10 | 10 | 10 |
| No. specimens containing food | 1 | 6 | 1 | 2 | 1 | 3 | 7 |
| Kind of Organism | |||||||
| Aphasmidia | 10.0 | 00.7 | ..... | 03.0 | ..... | ..... | ..... |
| Arthropoda | |||||||
| Araneae | |||||||
| Argiopidae | ..... | ..... | ..... | ..... | 04.0 | ..... | ..... |
| Theridiidae | ..... | ..... | ..... | ..... | 04.0 | ..... | ..... |
| Insecta | |||||||
| Ephemeroptera (nymph) | |||||||
| Baetidae | ..... | 05.0 | ..... | ..... | ..... | ..... | ..... |
| Heptagenidae | ..... | 08.0 | ..... | ..... | ..... | ..... | ..... |
| Hemiptera | |||||||
| Corixidae | 35.0 | 00.3 | ..... | ..... | ..... | ..... | ..... |
| Hymenoptera | |||||||
| Formicidae | ..... | 21.0 | ..... | ..... | ..... | ..... | 60.0 |
| Coleoptera | |||||||
| Staphylinidae | ..... | 01.7 | 07.0 | ..... | ..... | ..... | ..... |
| Scolytidae | ..... | 13.3 | 70.0 | ..... | ..... | ..... | ..... |
| Tenebrionidae | ..... | 05.7 | ..... | ..... | 70.0 | ..... | ..... |
| Carabidae | ..... | 05.7 | ..... | ..... | ..... | 01.0 | ..... |
| Curculionidae | ..... | 01.0 | ..... | ..... | ..... | ..... | ..... |
| Coccinellidae | ..... | ..... | ..... | ..... | ..... | ..... | 09.0 |
| Trichoptera (case) | ..... | 01.7 | ..... | ..... | ..... | ..... | ..... |
| Diptera | |||||||
| Mymaridae | ..... | 00.3 | ..... | ..... | ..... | ..... | ..... |
| Empididae | ..... | 01.3 | ..... | ..... | ..... | ..... | ..... |
| Cecidomyiidae | ..... | ..... | ..... | ..... | 04.0 | ..... | ..... |
| Trachinidae | ..... | 00.7 | ..... | ..... | ..... | ..... | ..... |
| Simulidae | ..... | 06.7 | 20.0 | ..... | ..... | ..... | ..... |
| Tabanidae | ..... | ..... | ..... | ..... | 06.0 | ..... | ..... |
| Chironomidae | ..... | ..... | ..... | ..... | 06.0 | ..... | ..... |
| Not identified to family | ..... | 01.0 | ..... | ..... | ..... | ..... | ..... |
| Orthoptera | |||||||
| Locustidae | ..... | 07.7 | ..... | ..... | ..... | ..... | ..... |
| Tettigoniidae | ..... | ..... | 03.0 | 70.0 | ..... | ..... | 09.0 |
| Tetrigidae | ..... | ..... | ..... | ..... | 06.0 | ..... | ..... |
| Homoptera | |||||||
| Fulgoridae | ..... | 05.0 | ..... | ..... | ..... | ..... | 01.0 |
| Insect egg | ..... | 00.7 | ..... | ..... | ..... | ..... | ..... |
| Plants | |||||||
| Cyanophyceae | ..... | 09.0 | ..... | ..... | ..... | 99.0 | 20.0 |
| Cyperaceae | ..... | 02.0 | ..... | ..... | ..... | ..... | 01.0 |
| Zannichellia palustris | ..... | 00.3 | ..... | ..... | ..... | ..... | ..... |
| Vascular remains | 55.0 | ..... | ..... | 27.0 | ..... | ..... | ..... |
| Miscellaneous | |||||||
| Sand | ..... | 00.7 | ..... | ..... | ..... | ..... | |
| Pharyngeal tooth | ..... | 00.3 | ..... | ..... | ..... | ..... | ..... |
| Total (%) | 100.0 | 99.8 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
Spawning apparently occurs when river levels recede to the seasonal lows. In late summer, temperatures of these rivers probably are maximal, their turbidities are reduced, and their sandy bottoms are stable. Underhill (1959) reports that this species is rare in the Vermillion River, a northeastern tributary of the Missouri River, except in autumn when large numbers occur near the mouth of the river. We suspect that this is associated with spawning.
Distribution of collections examined.