Date of Award


Degree Type


Degree Name

Master of Science




Biology (MS)

First Advisor/Chairperson

Dr. Jill B. K. Leonard


Cisco, Coregonus artedi, are highly sensitive to environmental variability which likely contributes to the speciation within the Great Lakes cisco clade. Hatcheries are trying to supplement cisco due to population declines. However, hatchery-reared cisco develop flat, subterminal snouts in hatchery environments instead of the pointed, terminal mouth observed in the wild. The cause and onset of the malformation could be the result of physical trauma, diet, genetic predisposition, or responses to an unusual rearing environment. We determined the stage of malformation onset by comparing hatchery-reared cisco (Jordan River National Fish Hatchery) to wild-caught cisco (northern Lake Huron) using geometric morphometrics. Our results suggest that the onset of malformation begins by preflexion, and possibly earlier, during early ontogeny and the beginning of endochondral ossification. The malformation is characterized by an improperly formed vomer and ethmoid bone. Early onset of the malformation suggests physical trauma is not the sole causative factor, and supports diet and/or environment as triggers in the malformation. Further, we tracked the progression of the malformation in juvenile cisco using temperature and density in four treatment groups: low density (LD) warm (12.5℃), high density (HD) warm, LD cold (8℃), and HD cold. As predicted, warm water cisco grew faster than cold water fish, and lower density groups grew better than high density groups. For our trajectory analysis, there was no significant difference between our treatment groups with respect to facial morphology suggesting the malformation develops early and continues to progress into juvenile stages despite temperature or density adjustments.

Access Type

Open Access

Justification for Restricting Access

I am hoping to publish my thesis and having it available online for everyone to see may restrict my chances of getting published elsewhere.

Available for download on Tuesday, June 29, 2027

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Biology Commons