Proposed Revision of the Standard-Weight Equation for Rainbow Trout

We developed standard-weight equations for rainbow trout by applying the regression-line-percentile (RLP) technique to samples from 81 lotic and 50 lentic populations from across North America. Because the length-weight relationship differed between lotic and lentic fish populations, we developed separate equations for those populations. They are log10Ws= −5.023 + 3.024log10TL (lotic) and log10Ws= −4.898 + 2.990log10TL (lentic), where Ws is the standard weight in grams and TL is the total length in millimeters. The equivalent English-unit lotic and lentic RLP equations are log10Ws= −3.432 + 3.024log10TL and log10Ws = −3.354 + 2.990log10TL, respectively, where Ws is the standard weight in pounds and TL is the total length in inches. Computed Wr values using the RLP equations did not systematically change with increasing fish length. Significant differences in Wr were not observed between samples from lotic and lentic populations or among length categories when our RLP equations were used.