190 



FISHERY BULLETIN OF THE FISH AXD WILDLIFE SERVICE 



ing ground. Figure 6 clearly illustrates a spawn- 

 ing mark ( S. M.) formed a year previous to 

 capture. 



5. Striae. — These markings are line ridges in the 

 surface layer covering the anterior portion of the 

 scale. They are very close together and run lat- 

 erally across the scale in contour with the trans- 

 verse grooves: figure 7 shows them clearly. 

 (i. Transvi rse grooves. — These are distinct grooves 

 in I he surface of the anterior, sculptured por- 

 tion, crossing it laterally en the same general 

 contour as the striae, but spaced farther apart. 

 Some of the grooves are continuous lines running 

 from one edge of the scale to the other: others ex- 

 tend in from both sides without meeting in the 



.piVZ 



Figi re 3— Scale from a juvenile shad, probably 4 or S 

 months old, caught while still in the river. There are 

 only two transverse grooves. Had this shad lived longer 

 the scale would have funned the fresh-water zone Of 



i he larger scale. 



Figure 4. — Enlargeit view ol margin of the scale from a 

 shad just entering the Hudson River on its spawning 

 migration. 8 



Figuhe 5. — Enlarged view of scale from a shad taken on 

 the spawning ground after a period in fresh water. 1 



center of the anterior field. Some of the grooves 

 start as a single line at the edge of the settle and 

 then branch to form two lines. 

 7. Baseline. — In this paper the baseline is con- 

 sidered to be the first transverse groove on or just 

 anterior to the demarcation line between the an- 

 terior and posterior fields of the scale (also see A 

 in fig. 8 ). 



PREPARING AND READING SCALES 



The settles used in this study were collet-ted dur- 

 ing the spring of L950, from Hudson River shad, 

 for use in age, growth, and mortality studies. 

 Many of the settles taken could not be used, either 

 because they were regenerate scales (fig. !*). or be- 

 cause they were asymmetrical and could not be 

 read. Four hundred nonregenerate and symmet- 

 rica] scales were chosen at random from the collec- 

 tion. Twenty scales. 2 each from 10 fish, were im- 

 pressed on individual •">" x 5" plastic sheets using 

 pressure and heat. Some settles were mounted in 

 glycerine jelly .ami polyvinyl alcohol on glass 

 slides to compare their readability with settle im- 

 pressions on plastic. As far as we could deter- 

 mine, the one method is as good as the other, but 

 since plastic impressions are easiei to handle and 

 less bulky to file, this method was used. 



2 Photographs from an unpublished manuscript nf Lnuelln K. 



CM.. 



