188 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



-31 



Figube 1. — A scale from a female shad measuring i'-'j inches and weighing 6% pounds. There are five annuli and five 

 spawning marks, and the fish was spawning for the sixth time, which makes it 11 years old. The Roman numerals 

 I through V represent the annuli, and VI through X the spawning marks. The Arabic numerals indicate the fol- 

 lowing: 1. annuli, or winter rings; 2, false annuli, or accessory rings; 3, fresh-water zone; 4. spawning marks: 5, 

 striae; 6, transverse grooves: and 7, the baseline. 



the surface area. The anterior portion has seven 

 types of visible markings that are indicated by 

 Arabic numerals on figure 1, as follows: 

 1. Annuli, or winter rings. — These are the lines 

 seen on the surface of the scale following the con- 

 tour of the periphery through both the anterior 

 and posterior portions. 1 The annuli are usually 

 most clearly seen in the lateral fields of the an- 

 terior portion neat the baseline. On some scales 

 they show very clearly on a diagonal line running 



1 For optical reasons, the posterior areas of Hit* annuli cannot 

 he seen in this photograph. They may, however, be seen during 

 microscopic reading of t tn - scale bj changing direction of the 

 lighting. 



from the center of the baseline to the shoulders 

 of the scale. 



■1. Falsi annuli. — These are also called accessory 

 rings and are similar in appearance to true annuli. 

 ( )n easily read scales they do not show tip as clearly 

 as do the annuli, and are not usually found cir- 

 cling into the posterior portion of the scales 

 studied. These marks make age determination 

 from shad scales difficult. Notice the less-empha- 

 si/.ed false annuli between the true ones on the 

 settle shown in figure 2. 



•'>. Fresh-water zone. — This is an important false 

 annulus found on till shad scales and is laid down 



