Standard weight in fish

Length measurements reported for fish may be of the fish's total length, fork length, or maximum standard length. For standard weight equations, the total length is used. In some species, male and female fish have different standard weight curves. For example, Anderson and Neumann report different standard weight equations for male and female paddlefish. Some researchers have also reported separate standard weight equations when a species has lentic (living in still water) and lotic (living in flowing water) populations. For example, separate standard weight equations have been published for lentic and lotic rainbow trout. ==Applications==

Standard weight is used as a basis for comparison to assess the health of an individual or group of fish. Generally, fish that are heavier than the standard weight for their length are considered healthier, having more energy reserves for normal activities, growth and reproduction. Fish may weigh less than expected for their length for many reasons, and a scientist must consider more information before assigning a cause. One of the simplest reasons is lack of food/prey. Lack of prey in turn could be the result of overpopulation of the predator, for example, competition from another predator species, unsuitability of the environment for reproduction of the prey, or dying of the prey for some reason. A fish may also weigh less than expected due to a change in activity level or metabolism due to some environmental factor. Standard weight equations, together with some measure of a fish's condition, can be used in aquaculture to measure the effectiveness of various feeding, temperature control, containment or other practices. The actual measure of a fish's condition using standard weight is done different ways. The relative weight (Wr) of an individual fish is its actual weight divided by its standard weight, times 100%. A fish of "normal" weight has a relative weight of 100 percent. The relative weight of a fish does not indicate its health on a continuous scale from 0 -100%, however. For example, Simpkins et al. found that juvenile rainbow trout with a condition index of less than 80% were at a high risk of dying. Relative weight is one of several common measures of condition used in fisheries assessment and management. Fulton's condition factor, K, is another measure of an individual fish's health that uses standard weight. Proposed by Fulton in 1904, it assumes that the standard weight of a fish is proportional to the cube of its length: K = 100(W/L^3)\!\, where W is the whole body wet weight in grams and L is the length in centimeters; the factor 100 is used to bring K close to a value of one. File:Black Drum Weight vs. Length Calcasieu Estuary metric.png| File:Red Snapper Weight vs Length.jpg| File:Schoolmaster Snapper Weight-Length.png| File:Pompano WL.png| File:Tigermuskielw.png| File:Gafftopsail WL.png| File:Spotted Seatrout Weight Length.png| ==See also==

• Beamesderfer, R.C. A Standard Weight (Ws) Equation for White Sturgeon. Calif. Fish and Game 79(2):63-69, 1993 • Bister, T.J. Proposed Standard Weight (Ws) Equations and Standard Length Categories for 18 Warmwater Nongame and Riverine Fish Species North American Journal of Fisheries Management 20:570-574, 2000 ==External links==