To find out whether actual differences existed 

 between scales of adult fish released as fry and 

 those from adults released as fingerlings, we 

 selected scale samples from brood year 1956 

 because that year had the largest number of 

 specimens that were released as fry. Returns 

 of fish released as fingerlings are plentiful for 

 analyzing this group in any brood year. 



In 1959, eight fall chinook salmon with Ad- 

 LP mark (released as fry) were recaptured. Of 

 these, seven were 3 years old and therefore 

 came from 1956 brood. In 1960, 28 such marked 

 chinooks were recaptured and 16 of these were 

 4 years old and of the 1956 brood. This total of 

 23 scales that belonged to the 1956 brood, plus 

 102 3-year-olds that were recaptured in 1959 

 with Ad-RP marks (released as fingerlings) 

 and 167 4-year-olds that were recaptured in 

 1960 with the same mark, provide the samples 

 for the following study. 



Based on theoretical considerations given 

 earlier, we used two purely objective methods 

 aimed at detecting any diff"erence these two 

 groups of scales might have in growth in fresh 

 water or the first year of growth in the sea. 



The first objective method was that of com- 

 paring growth patterns revealed by scale 

 graphs based on spacing of circuli. Under a 

 magnification of 140 times, the circuli were 

 marked along the antero-lateral radius on a 

 millimeter graph paper. We then divided the 

 radius into 20-mm. units and calculated the 

 mean spacing of circuli of each unit. For each 

 group of scales, the means of circulus spacing 

 of a unit were summed and averaged to give 

 the mean of the group. When the group means 

 were plotted on the ordinate against the radius 

 units on the abscissa, we obtained a scale graph 

 which shows the growth pattern. 



Figure 2 shows information on groups re- 

 leased as fry and as fingerlings. 

 The fresh-water growth part of figure 2 shows 

 a similar pattern for the two groups, namely, 

 circuli are wide at the start but rapidly narrow 

 down : the extent of growth covers about the 

 same distance on scale radius. Also, there is 

 only a slight difl'erence in the mean spacing of 

 circuli. Such difference, as will be shown in the 

 second method, is not statistically significant. 



S 6 



?. 4- 



■ MARKED FRY. N = 16 

 -MARKED FINGERLING. N=17 



12 3 4 5 6 7 8 



DISTANCE FROM FOCUS ALONG ANTERO-LATERAL 

 AXIS IN 20-MM UNITS (XMO) 



FIGURE 2 



Figure 2. — Spring Creek Hatchery chinook salmon: 

 Mean scale graphs showing pattern of fresh-water 

 growth and the major portion of first year's marine 

 growth of group marked as fry (solid line) and of 

 group marked as fingerlings (dash line). 



Marked difference, however, is evident in the 

 marine growth section of figure 2 (units 4 to 8). 

 The group released as fry has much wider cir- 

 culi at every unit than has the group released 

 as fingerlings. This is, of course, only a reflec- 

 tion of group difference, as the values plotted 

 are mean widths. At each unit, the mean cir- 

 culus widths of the two groups of scales overlap 

 widely so that we could not identify the group 

 origin of individual scales on that basis. Ex- 

 amples of scales of adults that were released as 

 marked fry and as marked fingerlings are 

 shown in figures 3 and 4. 



The second objective method, aimed at detect- 

 ing differences in first year growth of fish 

 released as fry and as fingerlings, was to meas- 

 ure and compare the total distance of the first 

 5 circuli, of the first 10 circuli, and of 10 circuli 

 counted from the 16th through 25th circulus. 



The reasons for the selection of these three 

 measurements are as follows: Fish released as 

 fingerlings have developed, in the hatchery, 

 the first 5 circuli and most, if not all, of the first 

 10 circuli ; but the fry that are released develop 

 all circuli in the natural environment. We 

 measured the first 5 and first 10 circuli, there- 

 fore, to detect differences in initial fresh-water 

 growth. The third measurement, distance from 

 the 16th through 25th circulus, was made to 



SCALES OF CHINOOK SALMON 



169 



