Biology ETDs

Publication Date



Life history aspects of Roundnose Minnows, Dionda episcopa, were examined for specimens collected between 2011 and 2013 in El Rito Creek, near Santa Rosa New Mexico. A recent study examining DNA suggested that, instead of supporting a widespread population of the Roundnose Minnow, New Mexico is actually home to two evolutionarily distinct Roundnose Minnow populations. This focus of this study is on the life history attributes of what may become a newly described species of Dionda. Modal class progression analysis (Bhattacharya method) documented four distinct age classes of Roundnose Minnows within El Rito Creek. Sex ratios deviated from the expected 1:1 ratio in 2011, 2012, 2013, and for the study period as a whole. In all cases, sex ratios were biased towards females. Mean female GSI values show statistically significant peaks during 2011 and 2012, with little statistical differences among 2013 mean monthly GSI values. Water quality had little explanatory power in predicting mean female GSI values when included as dependent variables in regression models. Microscopic examination of a sub-set of female gonads documented sexually mature females as small as 34 mm standard length. Larval specimens of Roundnose Minnow occurred in nearly every sample in which that life stage was targeted for collection. These included all 2012 collections; the only complete calendar year during the study period. The continual collection of larval fish indicates some level of year round spawning by adult Roundnose Minnow. Because artesian discharge is the primary water source for El Rito Creek, relatively stable water temperatures and habitat conditions could be favorable to year-round spawning by Roundnose Minnow. Continuous spawning, female biased sex ratios, and female sexual maturity at a relatively small size suggest a population that has a high intrinsic rate of increase and can sustain high turnover rates.

Project Sponsors

New Mexico Department of Game and Fish




Life history, Roundnose Minnow, Dionda epeiscopa

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Advisor

Turner, Thomas F.

First Committee Member (Chair)

Ross, Stephen T.

Second Committee Member

Wolf, Blair O.