of the Fishery Board for Scotland. 213 
Most work of this kind, by making use of the hard structures of fish 
as a guide to their probable age, has been done by Professor Heincke and 
his coadjutors at the Biological Institute of Heligoland. The results are 
not yet fully pnblished, but Professor Heincke has given some of his 
conclusions in two recent publications.* The investigation was made on 
the cod on the German coast and at Heligoland, a fact to be kept in 
mind, as it is possible that on the shallow coast on the other side of the 
North Sea, where the saltness of the water is less than on this side, the 
cod grow less quickly than they do on the western side, as appears to be 
the case in the Baltic. Heincke estimates the size of the cod in the 
southern part of the North Sea as follows :— 
Year. Range of Sizes. Average Size. Increase, 
Cm. | Inches. Cm. Inches. Cm. 
In first year, - -| 8-18 34-74 14 5} 
In second year” - _ — about 27 102 13 
In third year, - - -- -- », 930-40 138-153 10 
In fourth year, - -- -- » 45-50 172-192 10 
He says they have learned from a study of the bones that a cod of 50cm. 
(192 inches) ‘“‘has lived at most four complete years, and we believe— 
provisionally—that the cod does not spawn for the first time until it has 
lived four complete years, probably at the end of its fifth, at latest the 
sixth year.” And, again, in the later paper, that it does not become 
sexually ripe until the completion of the fourth year, and perhaps only 
after the completion of the fifth year, when the average size is between 
55cm. and 60cm. (213-234 inches). 
After spawning, the rapidity of growth diminishes, as in other fishes, 
so that a cod of 75cm. (294 inches) is at least 7 years, and probably 8-9 
years old; one of 85cm. (333 inches) at least 8, and probably 9 or 10 
years old, and one of 100cm. at least 10, and probably 12 or more years 
of age. Young cod, under one year of age, were found to grow in the 
aquarium at Heligoland, when well fed, not less than 1mm. daily (or at 
a rate of about 14 inches a month) from the beginning of August to the 
middle of September, and from the middle of September to the end of 
October 4 to 3 of a millimetre daily; and it is stated that growth in the 
open sea would certainly be greater. As stated in my previous paper, a 
cod of 11? inches in the tank at the Laboratory at Aberdeen grew to 
122 inches between 28th August and 26th September, or at the rate of a 
millimetre per day. 
Mr J. T. Cunningham has also studied the rate of growth or age of cod 
by the markings on the hard structures, but his conclusions do not quite 
agree with those of Professor Heincke, and he differs also as to the 
structures best fitted to show the growth.f Professor Heincke found the 
otoliths and scales much less satisfactory than the bones, and particularly 
the coracoid and scapula, especially in the cod, “which, for the rest,” he 
says, “is one of the most difficult species on which to determine the age.” 
On the other hand, Cunningham found these bones and others of the cod 
unsuitable for the determination of the age, it being impossible, he says, to 
distinguish with certainty the annual rings or zones. Speaking of the 
*« The Occurrence and Distribution of the Eggs, Larve, and Various Age-Groups 
of the Food-Fishes in the North Sea.” Conseil Perm. Intern. pour L’Explor. de la Mer, 
General Report on the Work of the Period, July, 1902-July, 1904, p. 29, 30; Die 
ie) ela: Deutschlands an der Internationalen Meeresforschung, III. Jahresbericht, 
p. 75. 
+ Twenty-third Annual Report Fishery Board for Scot., Part III., p. 181 et seq. 
