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The condition index in fish is a way to measure the overall health of a fish by comparing its weight with the typical weight of other fish of the same kind and of the same length. The condition index is its actual weight divided by its expected weight, times 100%. A fish of normal weight has a condition index of 100 percent. So if a tarpon, for example, has a condition index of 104 percent, that would mean it is above the normal weight for an average tarpon of that length. If a tarpon has a condition index of 92 percent, that would mean that it is thinner, or below the normal weight of other tarpon that length. The condition index depends on how much a fish is eating compared to the energy it has to spend to live, migrate, reproduce, and do its other activities. The condition index for fish is a simple measurement that can be used to provide important biological information that can then be used to make better management decisions. ==Definition and Calculation== The condition index in fish is a way to measure the overall health of a fish by comparing its weight with the average weight of other fish of the same length and kind.〔( Southern Illinois University slide presentation describing Condition Index and Relative Weight in fish. ) Accessed 26 August, 2011.〕 To do this, a weight-length relationship that is published in a journal or a reliable report is used to make the comparison. Some weight-length relationships are for a group of the same fish from a certain location; others are developed from lots of data from different locations and represent a more general result. Some studies have enough data to develop separate weight-length relationships for male and female fish of the same species, and/or to develop separate weight-length relationships for different seasons of the year (e.g. Spring and Fall). To compute the condition index of an individual fish, it must be weighed and its length measured. Some weight-length relationships use the total length of the fish while others use the fork length. It is important to measure the same kind of length that the reference relationship uses. It is also important to have the weight and length in the same units as the reference relationship. The reference weight-length formula is used to calculate how much the individual fish would be expected to weigh based on its measured length. Then the condition index is the actual weight of the fish divided by its expected weight, times 100%. A condition index greater than 100% means the individual fish weighs more than expected, while a condition index less than 100% means the individual fish weighs less than expected for its length. Since the condition index is used to assess the health of fish, it is important to have a reliable reference weight-length relationship. For example, a red drum (''Sciaenops ocellatus'') caught in the spring in waters off of the Gulf Coast of Louisiana, U.S., is expected to have a weight-length relationship of W = 0.000005297L3.110, where W is the weight in grams and L is the total length in millimeters.〔Jenkins, J.A. Fish Bioindicators of Ecosystem Condition at the Calcasieu Estuary. National Wetlands Research Center, USGS Report 2004-1323, 2004.〕 Consider one red drum that is 400 millimeters long and has a weight of 616 grams. Based on the reference weight-length relationship, a red drum that is 400 mm long is expected to have a weight of 655 grams. The condition index for that fish is its actual weight divided by its expected weight times one hundred percent, or (616g/655g)x100% = 94%. The fish in this example is below its expected weight, and a scientist might then look for more information to find out if other red drum in the area are also below expected weight. If red drum in the study area tend to be below expected weight, then the scientist might further investigate why this might be. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Condition index」の詳細全文を読む スポンサード リンク
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