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Kansas Cooperative Fish and Wildlife Research Unit

Casie Lee (2013)

Casie Lee (2013)- The Thrill of Victory, the Agony of Defeat: Developing and Testing a Standard Protocol for Field Estimates of Short Term Growth in Fish Predators. (Mentor: Martha Mather)

In aquatic ecosystems, motile predators have the capacity to increase their growth rate and size by moving to areas with favorable conditions and avoiding those with adverse conditions. Understanding field estimates of short-term growth (days to weeks) can offer insight into organismal condition in relation to movement, other behaviors, and habitat variables such as temperature, physical structure, and availability of food. However, field-based estimates of short-term growth are limited. Diets offer hour-scale estimates of organismal nutrition but are highly variable. Stable isotope analysis can provide long-term approximations (months to years) of nutritional status but is not sensitive to temporal patterns. Alternatively, the ratio of RNA-DNA (RNA:DNA) may reveal an intermediate window of growth. In our study, we asked (1) if a standard protocol for RNA:DNA analysis existed in the literature for field-caught fish, (2) if this protocol yielded consistent results, and (3) how differences in sampling and analysis procedures contribute to sources of variability. We first searched the literature and compiled research papers on RNA:DNA analysis methods for both field-sampled fish and fish raised in controlled laboratory settings. From the literature, we summarized a standard protocol that reflected methods currently in use to evaluate short term growth of field-caught fish. This protocol was then tested on a set of hatchery-reared channel catfish, Ictalurus punctatus (170-300 mm TL). Subsequently, several sources of variability in sample collection, preservation, tissue processing, and nucleic acid analysis were examined. Based on trials of 332 fish, we obtained an improved, tested, and validated protocol that can be used to examine predator growth in Kansas reservoirs. However, although potentially very useful, the sensitivity of the analysis to environmental and methodological circumstance suggests that this tool be used and interpreted with caution.