238 



Part III. — Seventeenth Annual Report 



together with their average size. As the principal hatching time for 

 plaice on this coast is April, and the young fishes after having passed the 

 pelagic post-larval stage are found on the sands in June and July, the 

 plaice that were captured in April (Series X.) must be one year old or 

 more. The measurements show the average size of the youngest group of 

 65 fishes to be 77*2mm., which therefore indicates the average growth of 

 the plaice during the first year. The average size of the second group in 

 Series X. is 156 'Omm., and represent the tw T o-years old fish. The differ- 

 ence between these two averages is TS'Smm., and should indicate the 

 second year's growth. As there is no reason why the difference in size 

 between the first and second, and between the second and third groups 

 should not be the same the whole year round and respectively equal to 

 the second and third year's growth, a comparison of these groups will 

 be of value, and may serve as a basis for calculating the growth-rate 

 during the various years. 



TABLE IV. 



Showing the Eesult of Comparison between A and B, and between 



B and C Groups. 



Order of the Series 

 comparable, 



in. 



IV. 



V. 



VI. 



VII. 



X. 



Mean Yearly 

 Increase. 



Difference in aver- 

 age size between 

 A and B groups, 



77-4 



79-4 



78-2 



69-0 



94-3 



78-8 



79'5 mm. 



Difference in aver- 

 age size between 

 B and C groups, 





78-5 



757 



(85-0) 



(66-5) 





76*4 mm. 



In Table IY. such comparisons have been made, and they show first of 

 all that, with the exception of Series YI. and YIL, the separation of the 

 various groups— A, B, and C — must be nearly correct, and also the calcu- 

 lated average size. The cause of the great irregularities in Series YI. and 

 VII. will be seen from Table III. Thus, in Series YI. the value of the B 

 group (135*0) is clearly too small, and so also is the A group in Series 

 YII. But when the somewhat limited number of fish that were examined 

 in some cases is taken into consideration, it is surprising that the calcula- 

 tions relating to the two first groups should compare so well. Owing to 

 the small numerical representation of the C group, less importance can be 

 attached to the average values that have been deduced. There appears, 

 however, so far as the data go, to be a recognisable decrease in growth- 

 rate during the third year. The above deductions from these experiments 

 may be summed up as follows : — 



1. The average growth of the plaice during its first year appears to be about 77 '2mm. 

 2 ,, second ,, 79*5mm. 



3. ,, third ,, 76*4mm. 



4. The total average length at the end of the first year appears to be about 77 '2mm. 



5. ,, second ,, 156'7mm. 



6. „ ,, third „ 2331mm. 



So far as these observations go, it would appear that the average linear 

 growth-rate of the plaice is a little greater in the second than in the third 

 year ; and w r hile from want of data it is not possible to prove anything 

 regarding the following (older) groups, it is natural that a continuous 



