YELLOW PERCH OF LAKE ERIE 



253 



the standard length of the fish increased above 

 270 mni. 



A comparison of the average actual weights 

 with the calculated weights shows that there was 

 excellent agreement over most of the length 

 range for which there were large numbers of fish.'* 

 Over the standard length range of 103 to 238 mm. 

 the actual weights at no point disagreed with 

 either of the computed weights by more than 3 

 grams. It is apparent also that calculated weights 

 obtained by the two equations agreed almost 

 equally well with the average actual weights over 

 this length range. The lack of agreement between 

 the observed weights and the computed weights 

 of perch with standard lengths less than 103 mm. 

 may be due to the small number of specimens of 

 that size. The empu'ical weights were somewhat 

 less than either calculated weight at all but three 

 of the lengths greater than 238 mm. (intervals 

 with midpoints at 258, 273, and 288 were the ex- 

 ceptions). Over this range, the weights calcu- 

 lated on the basis of the cubic relationship were 

 ordinarily closer to the observed weights than 

 were those calculated from the more general 

 equation. The fact that the actual weights of the 

 larger fish were usually less than the computed 

 weights may indicate that both equations fail to 

 fit the data exactly for standard lengths greater 

 than 238 mm., or it may be due to the small 

 number of individuals in most of the frequency 

 intervals. Another possible explanation of the 

 lower actual weights at lengths greater than 238 



» The average actual weights are the averages of all flsh in each 5-mm. 

 interval. Only the midleagth of each interval is shown in the table. 



mm. is that the gill nets selected only the lighter 

 of the longer fish. 



The weights calculated from the length-weight 

 equation, >F= 1.766 XIO"'!.'"", are shown graphi- 

 cally in figure 10. The use of two scales permits 

 ready conversion from metric to English units of 

 weights and measures. The factors needed most 

 frequently for conversions between standard, fork, 

 and total lengths are shown in table 30. It was 

 mentioned (p. 252) that intervals of standard length 

 that contained less than 28 fish were not used in 

 the determination of the general length-weight 

 equation. Hence, the points on the curve that 

 he below 106 mm. and above 250 mm. are outside 

 the range to which the cui-ve was actually fitted. 

 However, the closeness with which the extra- 

 polated portions of the curve (shown by broken 

 hues) fit the average actual weights based on few 

 specimens indicates that, in spite of the discrep- 

 ancies already mentioned, the curve is for practi- 

 cal purposes applicable to the length-weight rela- 

 tion over the entire range represented. 



COEFFICIENT OF CONDITION (K) 



The condition of fishes and fluctuations in the 

 values of the coefficient of condition (K) involve 

 problems that are distinctly different from the 

 description of the general length-weight relation 

 (see Hile 1936, for detailed discussion). Condi- 

 tion, or relative heaviness, is influenced b}' those 

 physiological and environmental factors that 

 affect the general well-being of the individuals. 

 The present data permit a description of the fluc- 



Table 30. — Factors for conversions between standard, fork, and total lengths of Lake Erie yellow perch 

 [Number of specimens employed to determine values of the factors are shown in parentheses] 



