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Updated: Jun 12, 2026

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems
Published on: July 30, 2019
Morphological responses of a stream fish to water impoundment
Travis C Haas1, Michael J Blum, David C Heins
1Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA. thaas@tulane.edu
Water impoundment alters fish body shape. Reservoir populations of Cyprinella venusta exhibit deeper bodies and smaller heads compared to river populations, driven by reservoir size.
Area of Science:
- Ecology
- Evolutionary Biology
- Ichthyology
Background:
- Water impoundment fundamentally alters river ecosystems, transforming them into reservoirs.
- The loss of natural flow and associated physical changes present unique ecological and evolutionary challenges for native aquatic species.
Purpose of the Study:
- To compare the body shape of Cyprinella venusta between river and reservoir habitats.
- To investigate the influence of reservoir characteristics on fish morphology and evolutionary divergence.
Main Methods:
- Geometric morphometric analysis was employed to quantify body shape differences.
- Cyprinella venusta populations were sampled from eight paired river and reservoir sites in the Mobile River Basin, USA.
Main Results:
- Significant body shape differences were observed between river and reservoir populations of Cyprinella venusta.
- Reservoir individuals displayed deeper bodies, smaller heads, more anterior dorsal fins, shorter dorsal fin bases, and ventrally positioned eyes compared to stream counterparts.
- The observed shape divergence was consistent across sites and correlated with reservoir size.
Conclusions:
- Physical characteristics of reservoirs act as significant drivers of morphological changes in native fish.
- Water impoundment emerges as a critical, underappreciated evolutionary force impacting aquatic biodiversity.
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