Proposed Standard-Weight (Ws) Equation and Size Structure Indices for Northern Snakehead

Relative weight and size structure indices are useful tools for fish biologists to characterize fish condition and fish size structure. However, a standard-weight (W-s) and size structure indices do not currently exist for Northern Snakehead Channa argus. We complied length-weight data from 4 established populations of Northern Snakehead in North America across five states and four drainages. We used the regression line-percentile (RLP) method to develop a standard-weight equation for Northern Snakehead. The RLP method uses the 75th percentile as a benchmark for standard weight. Based this approach, we propose a metric standard-weight equation as log(10)(W-s) = -5.142 + 3.0418 * log(10)(TL) with a minimum length of 200 mm; W-s is weight in grams and TL is total length in millimeters. For calculating proportional size distribution (PSD) we proposed the following length categories: stock, 190mm (7.5 in); quality, 340 mm (13 in); preferred, 420 mm (16.5 in); memorable, 550 mm (22 in); and trophy, 700mm (27.5 in). The population level indices developed in this study will provide fish biologists another set of tools to describe invasive Northern Snakehead populations in North America.