YELLOW PERCH IN SAGINAW BAY 



367 



Figure 1. — Saginaw Bay. 



to the point of scale collection, two body-scale 

 curves were required for the calculation of 

 growth. 



The two body-scale curves were based on "key" 

 scales taken from above and from below the 

 lateral line of: Fish collected from trap nets on 

 June 22, 1955 (386 fish) ; 80 selected (large and 

 small) fish captured in November 1955; and 84 

 young-of-the-year and yearlings (caught on vari- 

 ous dates) from the collections of the Fish Divi- 

 sion, Museum of Zoology, University of Michi- 

 gan. 2 Each key scale from below the lateral line 

 was taken from the third row below the line on 

 the left side of the fish and directly beneath the 

 sixth spine of the dorsal fin. The key scale from 

 above the lateral line also was removed from the 

 left side and came from the second row above 

 the line and below the insertion of the first dorsal 

 spine. The locations of the key scales were 

 chosen to be near the centers of the areas from 

 which routine samples were taken. 



2 The total length of these museum specimens was increased 

 by 2 percent for shrinkage. 



Some scales (about 1,400) were mounted on 

 glass microscope slides in a glycerin-gelatine 

 medium described by Van Oosten (1929). The 

 remaining scales were impressed on cellulose ace- 

 tate, 0.020 or 0.040 inch thick, by a roller press 

 similar to that described by Smith (1954). But- 

 ler and Smith (1953), demonstrated that method 

 of preparation does not affect the measurements 

 of scales. The examinations and the measure- 

 ments of scales were made by means of a micro- 

 projector similar to the apparatus described by 

 Van Oosten, Deason, and Jobes (1934) at the 

 magnification X 43. The length of each scale 

 and the distance from the focus to each annulus 

 were measured along the interradial space most 

 nearly collinear with the focus and recorded to 

 the nearest millimeter. 



Age analysis 



Ages were determined by counting the annuli 

 and are given in terms of completed years of 

 life. They are expressed by Roman numerals 

 corresponding to the number of annuli. Thus 



