192 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 7. — Scale from a small male shad. Note that ther 

 indicated by Arabic numerals. The second annulus is 

 during the winter just previous to this migration into fre 



reached were used in the attempt to develop 

 criteria for age analysis. Borodin's (1925) 

 method of age determination by transverse grooves 

 was tried. However, lie gave no clear definition 

 of what constitutes a complete or incomplete trans- 

 verse groove; since none that we could devise ap- 

 peared to give the desired results, this method was 

 discarded. 



While trying Borodin's method on the clearly 

 marked scales, we noticed that the number of 

 transverse grooves entering the fresh-water zone, 

 and also the first, second, and third annuli, were 

 almost constant from fish to fish. It was also ob- 

 served that the spacing between transverse 

 grooves, as with annuli. was proportional to 

 growth. In other words, the distance between 

 grooves heroines proportionally less as the fish 



e are in transverse grooves to the edge of the scale as 

 just within the periphery of the scale, and was formed 

 •sh water where the fish was caught. 



grows older and its growth slows. Since the for- 

 mation of grooves seemed to be a function of age 

 and growth, it appeared that their numbers might 

 be used as an index to the amount of growth taking 

 place in any period and to locate the true annuli 

 on scales that were confused by false annuli. 



To check these observations, counts were made 

 of the number of transverse grooves entering the 

 fresh-water zone, first, second, and third annuli 

 on the L64 easily read scales. Counting began with 

 the first transverse grooves above the baseline, and 

 grooves which branched were counted as one only. 

 All the transverse grooves entering the fresh-water 

 /.one from one side were counted, including those 

 that just touched the line enclosing the fresh- 

 water zone. Those counted included incomplete 

 grooves (not joined in the middle of the scale) as 



