Only perfect scales, preferably from the midriff section, where they grow first, 

 should be used for an examination. Also, a cei-tain number of scales — not only one — should 

 be used, since one may have picked a scale, recently fomed to replace a lost and older 

 one. For one's own personal use, the technique of such an examination is easily acquired. 



In case of a difference of opinion, one should always abide with the findings of a 

 fish biologist, since special training and experience are necessary for more minute 

 obsei^ations . 



In isolated cases, especially in cases of irregular and impeded growth, a correct 

 determination of age may become impossible or lead to low values. But even the aost per- 

 fect scales cannot be relied xxpan for an absolute correct determination of age. Incidental- 

 ly, the main gill cover of the gill cover apparatus may be sijnilarly used. 



Since I have discussed the possibilities of excessive loss in weight (under A), I will 

 give here — for the fishbreeder's use — a mathematical formula by which the "normal" ratio 

 between weight and length may be calculated. 



This algebraic 3rd power equation is based upon the mathematical theorem that "similar 

 bodies are proportional to the cubes of their similar distances". 



If we use P for weight, L for total length (from point of head to longest point of 

 tail), K for coefficient, v/e have the follow: ng equation i P eq. K x l3 . 



100 

 I found as coefficient the following suitable figures: 



For "normal" Galician carp K eq. 1.8 



For Tench K eq. 1.3 



For Rainbow trout K eq. 1.1 



For greater clearness I have drawn the developed function P for the values K = 1.1, 

 1.3, and 1.8, and for 5 L 25 (Fig. 2). The curves permit immediate determination 

 whether, for example, a 10 cm. carp has approximately "norrnal yreight". 



This formula allows calculation of the v/eight of a "normal" fish from its length and 

 vice-versa. 



Small differences alv/ays occur, of course, due to loss in weight, filled-up intestinal 

 tract, excessive development of gonads or over-feeding, 



I found in rainbow trout — by normal feeding — always a somewhat lower weight (as about 

 K eq. 1), and by over- fed specimens a somewhat higher weight (as about K eq. 1.2). 



