AGE DETERMINATION OF AMERICAN SHAD 



163 



Figure 1. — Scale from 6-year-old shad spawning for the second time. (Roman numerals 

 represent annuli, FWZ fresh-water zone, and SM spawning mark. ) 



this study was X-rayed using a method described 

 by Sutherhiud (1958). Marked fins were identi- 

 fied from radiographs by an enlargement at the 

 distal end of the radial bones extending partially 

 or completely across the area of separation from 

 the dermal fin rays ( fig. 2 ) . This method of classi- 

 fication of marked fish is in agreement with Stuart 

 (1958) wlio found from microscopic examination 

 that a palpable ridge was formed on marked fins 

 at the site of cutting. Marked fins were classified 

 according to the nmnber of fin rays regenerated, 

 regardless of the length of the rays, and placed in 

 tlie following categories: (1) no regeneration — no 

 fin rays; (2) one-third regeneration — one to three 

 fin rays; (3) two-thirds regeneration — four to six 

 fin rays; and (4) complete regeneration — seven to 

 nine fin rays (fig. 2). 



Pelvic-fin sections were classified as malformed 

 if there was no enlargement at the distal end of the 

 radials (fig. 3B, C). Missing fins were chai-ac- 

 terized by absence of radials or, in some specimens, 

 absence of the entire pelvic girdle (fig. 3A, D), 

 and absence of scar tissue at the site of fin 

 origin. Malformed and missing fins were termed 

 abnormal. 



From a study of 28 shad collected in 1956, it 

 was determined tlvat 11 had abnormal pelvic fins. 

 These included 4 males and 7 females of which 5 

 had malformed left or right pelvic fins and 6 had 

 eitlier the left, right, or both pelvic fins missing. 

 These fish ranged in age from 3 to 6 yeai-s. 



In 1957 fish with a variety of pelvic fin abnor- 

 malities were purposely collected!. Of the 132 

 shad sajnpled, 62 were classified as abnormal. 



