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 published, 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. 



In first year, - - 

 In second year 

 In third year, - - 

 In fourth year, 



Cm. 

 8-18 



Inches. 

 34-7| 



Cm. 

 14 



about 27 

 ,, 35-40 

 „ 45-50 



Inches. 

 10f 



13f-15f 

 17|-19| 



Cm. 



13 

 10 

 10 



He says they have learned from a study of the bones that a cod of 50cm. 

 (19| 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. (21f-23j inches). 



After spawning, the rapidity of growth diminishes, as in other fishes, 

 so that a cod of 75cm. (29 g inches) is at least 7 years, and probably 8-9 

 years old; one of 85cm. (33^ 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 l£ inches a month) from the beginning of August to the 

 middle of September, and from the middle of September to the end of 

 October £ to g 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 1 inches in the tank at the Laboratory at Aberdeen grew to 

 12g 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. t 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, Larvae, 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 

 Beteiligung Deutschlands an der Internationalen Meeresforschung, III. Jahresbericht. 

 p. 75. 



+ Twenty -third Annual Report Fisher// Board for Scot., Part III., p. 131 et seq. 



