76 Carrying Capacity, Productivity, and Growth 



be expressed numerically when weights and lengths of individual fish are 

 used for calculating some form of condition factor. 



Methods of Measuring Condition 



In order to describe the relative plumpness of a fish as a numerical 

 value, a formula involving the relationship of surface ( length ) to volume 

 (weight) is applied to the fish. The solution of this formula gives a 

 number known as a condition factor, that stands for a measurement of 

 relative plumpness: A fat fish of a given species and length will show a 

 higher condition factor than a thin fish of the same species and length. 

 By calculating these condition factors for an adequate number of fish of 

 one species and of a limited range in length, taken from a single body of 

 water during a limited period of time, and averaging them, one may 

 arrive at an average condition factor for the species under the experi- 

 mental conditions adhered to above. In this way, the range of relative 

 plumpness for a species may be defined, and cycles of relative plumpness 

 associated with seasonal feeding or other kinds of behavior may come to 

 light. 



Coefficient of Condition. One of the first formulas developed by 

 fisheries workers -^ for figuring relative plumpness required the use of 

 the weight of a fish in grams, and its standard length in centimeters ( the 

 standard length of a fish is the distance from the tip of the snout to the 

 base of, but not including, the tail fin ) . In this formula K, the "Coefficient 

 of Condition," is equal to the weight of the fish in grams times 100, 

 divided by the cube of the standard length in centimeters, thus: 



^ _ 100 W 



When this formula was used for figuring the coefficient of condition for 

 fish with laterally compressed but deep bodies, such as the white crappie, 

 or the bluegill, the numerical value of K usually ranged from 2.00 to 4.00. 

 Fishes with bodies of lesser depth, such as the largemouth bass, usually 

 had K values ranging from 1.00 to 3.00. The numerical values for K meant 

 nothing in themselves but allowed comparisons between individuals or 

 groups of fishes. 



Index of Condition. The use of the Coefficient of Condition K had one 

 great drawback, namely that the average fisherman and even most fish- 

 eries biologists were unable to "think" of fish in terms either of weight in 

 grams or of body lengths (without tails) in centimeters.-^ Fishermen were 

 used to measuring the maximum length of a fish with its mouth closed 

 and the tail pinched so that the longest rays of the tail were parallel to the 

 body axis. Lengths of fish were measured in inches and fractions of inches 



