Effects of Temperature and Dissolved Oxygen on Development and Survival of Embryos in Nests of Bluehead Chub Nocomis leptocephalus

Abstract

Temperature and dissolved oxygen (DO) are two fundamental environmental factors that shape metabolic demand, developmental rate, and survival in fish embryos. Because embryos rely entirely on diffusion for oxygen uptake and cannot move away from stressful conditions, even small shifts in temperature or oxygen availability can strongly influence early survival. Despite their importance, the combined effects of temperature and DO remain understudied in non-model species and in natural systems where embryos occur at high densities. The communal nesting system of the Bluehead Chub Nocomis leptocephalus and its nest associates provides an ecologically realistic setting in which these stressors may interact, as many species deposit eggs within gravel mounds where oxygen levels fluctuate and embryos develop in close proximity. This thesis experimentally examined how temperature and dissolved oxygen influence embryo physiology and performance within this communal nesting context. Using controlled laboratory experiments across multiple temperature and oxygen conditions, I quantified oxygen consumption, developmental progression, and survival for the combined embryos (Bluehead Chub and nest associates) within the multi-species reproductive aggregation. Oxygen use increased consistently with warming, reflecting higher metabolic demand at elevated temperatures, but did not differ with ambient oxygen level, indicating that embryos maintained metabolic activity even when oxygen availability was reduced. Developmental rate also accelerated with increasing temperature, yet this rapid growth came at a cost: survival declined sharply at the warmest conditions, and low oxygen further amplified mortality under high temperatures. Cooler environments supported slower development rate but produced the highest overall survival. Together, the results show that warming is the primary driver of embryo stress, with oxygen availability offering only a limited buffering effect. These patterns highlight that embryos in communal nests are highly sensitive to modest environmental changes, particularly because they cannot behaviorally avoid unfavorable conditions. As stream temperatures rise and oxygen levels fluctuate with climate change, the narrow environmental window required for successful embryo development may constrain reproductive success and ultimately the population resilience of Bluehead Chub and its diverse nest associates.