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DEPARTMENT OF THE XATAL SERVICE 



6 GEORGE V, A. 1916 



Assuming that the scales grow as the fish itself grows, we naturally conclude that 

 the growth of the scale bears a definite proportional relation to the growth of the body. 

 We can thus calculate the amount of the fish's growth each year by measuring the 

 distances between successive winter rings on the scale. The following simple method 

 was used to estimate the rate of growth of the fish from the scales. Two scales from 

 each fish were taken and the margins of the winter rings of each drawn with the 

 camera lucida. The centres of scales were placed to coincide in the figure and their 

 long axes to lie approximately at right angles. A line of a length proportional to 

 that length of the fish from which the scales were taken was ruled between the axes of 

 the scales, and its end joined by straight lines to the ends of these. Parallel to these 

 last lines others were drawn from the points where the winter rings cut the axes of the 

 scales to the median line, thus dividing it into lengths directly proportional to the 

 lengths of the fish at the end of every winter of its life. 



When we compare a length frequency curve for each age using the lengths calcul- 

 ated from the scales by the above method with that for the actual length of fish of 

 known age, we find the range of size is much greater in it, where we are dealing with 

 greater numbers of measurements, but the average lengths agree fairly closely. 



It was intended to determine the length, age and sex of a number of haddock to 

 find what, if any, difference of size there was between the male and female fish. The 

 few results seem to show that the difference of sex is not accompanied by a marked 

 difference in length. The following table shows the average size for each year as 

 calculated from the scales of twenty-two fish: — 



The rate of growth curve shown in Fig. 1 is made from the average yearly 

 lengths as determined from the scales of seventy-four haddock. This curve shows a 



