Use of Regional Standard Weight (Ws) Equations to Assess Body Condition of Brown Trout (Salmo trutta) from Metal-Contaminated Streams

Weight-length relationships provide a tool to assess the body condition of brown trout (Salmo trutta) populations inhabiting stream reaches where stressors, such as metals, have chronic, sub-lethal toxic impacts. A previously published brown trout standard-weight equation, Ws, overestimated Colorado brown trout weights. Weight-length data from 16 Colorado brown trout populations (n = 9, 8 16) were used to develop a regional standard weight (Wcl) equation based on fish from waters free of metal contamination. Relative-weights (Wr) were then compared between metal-contaminated and metal-free streams in Colorado using the Wcl equation. Brown trout Wr's were lower in metal contaminated streams than in stream reaches uncontaminated by metals. The development and use of regional standard weight equations is recommended to help assess the weight of brown trout inhabiting metal-contaminated stream reaches.