Several methods are available to estimate the weight of a fish. Some use length as well as girth measurements. Weight also can be estimated using only length measurements based on relationship between length and weight. Length-weight equations can be developed for specific waters, regions (e.g., states), or for a particular species.
Formulas containing length as well as girth are often most accurate for estimating weight, because the fatness or plumpness of the fish is accounted for. If only length is available, the most accurate weights often are estimated from length-weight relationships for specific waters or regions. For instance, in some waters fish might be relatively "skinny," and the weight estimate might be overinflated if based on a formula created from data on a water body where fish are "fat" or even "normal." That's why adding girth to the formula can help with accuracy. Formula's containing girth, however, also may not be as accurate as we'd like, because of inherent differences in the shape of fish and finding the right adjustment factor (or "shape" factor) to use in the formula. And it's important to measure girth carefully, and at the fish's fattest point, as girth estimates affect weight estimates powerfully.
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