Seasonal Changes in Condition of Appalachian Brook Trout

Reliable fish condition estimates help managers better understand ecosystem population dynamics. Therefore, our study objectives were to measure seasonal changes in percent dry weight and energy density (physiological-based measures of condition) of stream-dwelling Appalachian Brook Trout Salvelinus fontinalis, field-validate bioelectrical impedance analysis (BIA) models, and compare reliability of BIA and morphometric-based estimates of condition. Percent dry weight was highly correlated to energy density (R-2 = 0.93; J/g wet weight = -1,803.5 + 286.43 . [percent dry weight]), and the relationship was clearly different from those published previously for other salmonids. Significant seasonal changes in adult Brook Trout condition were observed and likely related to energy depletion from reproduction and changes in terrestrial invertebrate consumption. Adult percent dry weight peaked in early September and was lowest in February. Age-0 fish did not have large changes in measured condition between summer and winter. Bioelectrical impedance analysis was able to estimate adult mean monthly percent dry weight reliably; however, it did not appear to outperform results from relative weight (W-r). Neither W-r nor predicted percent dry weight from BIA was a reliable estimator of condition for individual adult fish. The BIA model for age-0 fish was unable to provide reliable predictions for either individual fish or monthly mean estimates, due in large part to the small range in measured condition. The BIA estimated monthly mean energy density more reliably than did W-r. Overall results of this study indicate that BIA did not performappreciably better than W-r, which requiredmuch less effort to collect. Potential BIA model improvements may be possible by accounting for changes in skin temperature. Until improvements in the Brook Trout BIA models occur, their use should be limited to estimating mean energy density.