Razorback Sucker Differential Gene Expression

The potential for deleterious effects of hypolimnetic dam releases on native fishes in the Colorado River Basin has received considerable attention. Previous research demonstrated that reduced temperature decreases growth rates and suggested that developmental rates were reduced in Razorback Sucker, but these assessments did not quantify how development and growth co-vary in differing temperatures. Quantifying differential effects of rearing temperatures on growth and development may lead to a better understanding of temperature-mediated sources of mortality in the larval life stage (e.g., predation via smaller size or poorer resource acquisition via slower development). Because previous work demonstrated reduced growth at temperature ranges experienced by wild Razorback Sucker in the Colorado River Basin, we assessed how size and development co-vary in comparable thermal regimes. We hypothesize lower stream temperatures, compared to historical conditions, result in less-developed larval fish at similar sizes potentially limiting their mobility and ability to access off-channel rearing habitats. We first compared size at development for wild-collected larval Razorback Sucker from a cold and warm year in the San Juan River. Second, we reared hatchery-spawned larval Razorback Sucker at three different temperatures in the laboratory to isolate the effect of temperature on size at development. Finally, we obtained functional transcriptome-wide data through RNA-sequencing of the lab-reared fish to identify molecular pathways that are influenced by temperature and may affect growth and development through this life-stage.