Devils Hole pupfish (Cyprinodon diabolis) are morphologically distinct from closely related species by having a smaller body size with a large head and lacking pelvic fins. Manipulative experiments in closely related species have established a proposed mechanism for their morphological differences and have shown that environmental variables, specifically high temperatures and limited food availability, have effects on hormones and growth leading to vastly differing morphologies. The Ash Meadows Fish Conservation Facility houses a captive population of the endangered Devils Hole pupfish in a 100,000-gallon refuge tank designed to mimic the extreme desert habitat and ecosystem of Devils Hole. It is well established that environmental parameters contributed to altered morphology and behavior of C. diabolis in past refuge populations, but the population at Ash Meadows is exposed to less environmental variation. Herein, we capitalize on breeding events in the refuge environment and in a lab environment to compare growth rates and morphology of larval and juvenile fish to those derived from wild collected eggs. We also compare data from C. diabolis to previous studies on closely related species to tease apart environmental vs genetic effects on morphology. Understanding early patterns of growth may provide insight to morphological changes in adulthood that are important considerations in management of the captive population.