Effect of lipid levels and size in invasive carp overwinter survival.
Recruitment is one of the most important dynamic rate functions (i.e., recruitment, growth, and mortality). Often, recruitment can be heavily dependent on overwinter survival. Wintertime presents thermal and metabolic challenges to fish. Studies have suggested that overwinter survival and mortality is correlated to lipid content before entering winter. Inadequate lipid reserves are related to poor condition and may lead to overwinter mortality. Young fish need to accumulate adequate lipid reserves before entering winter. In the Mississippi River, where silver carp Hypophthalmichthys moltrix Valenciennes, 1844 are hyper abundant, silver carp are not experiencing recruitment issues. As such, we evaluated lipid levels and size as potential silver carp recruitment regulators. Silver carp were collected by the Long Term Resource Monitoring element in 2015 on the middle Mississippi River using mini fyke nets; total lengths ranged from 34-177 mm. Lipid levels of whole carp were determined using the phosphovanillin assay. No difference in lipid levels (mg/g) was observed between spring and fall fishes. Additionally, we observed no relation between total length and lipid levels. Size structure did not significantly differ between fall age-0 and spring age-1 silver carp. Our results suggest there may not be a size dependent overwinter mortality/survival in silver carp in the middle Mississippi River. Additionally, lipids may not be a driving factor in overwinter mortality/survival. Our research suggests silver carp in the Mississippi River basin do not follow most early life history paradigms and may explain the successful nature of the silver carp invasion.