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Part III. — Twenty-third Annual Report 



(2) Length of fish J/.5'6cm. {18 1 in.), 2\ lbs. tveight. — Scales behind 

 head show two winter zones besides the external edge, in other words 

 three annual zones. First zone 12 rings, second 17 to 19, third about 13. 

 Otolith also shows three aunual zones quite distinctly. Inferred age 

 three years. 



(S) Length of fish 67 5cm. (;? ft. 3 in.), 8^ lbs. weight— <$ with 

 small ovary, apparently immature. Scale from pectoral region shows 

 three winter zones besides the outer edge, in other words four annual 

 zones complete. The first zone contains 14 rings, the second 20, the 

 third 16, the last only 7. It might be supposed that the last zone was 

 only the commencement of the present season's growth, or, on the other 

 hand, the fourth winter zone might not be complete, as the water is still 

 cold in March. I thought it most propable that the fish was four complete 

 years old. In the transverse section of the otolith four complete zones 

 were visible. In this specimen I examined the pectoral girdle and the 

 concave faces of the vertebra?. In the coracoid I could with difficulty 

 make out three boundary lines in addition to the outer edge, but they 

 were very indistinct, and would be untrustworthy without the other 

 indications. In the hollows of the vertebra? there were numerous con- 

 centric lines, but the boundaries of annual zones were not distinct. 



According to these latter results, the cod at two years of age is 10 to 13 

 or 14 inches in length, at three years 17 to 19 inches, at four years 27 

 inches; but of course it would require the examination of a large number 

 of specimens to ascertain the average and range of sizes at these ages. 



Specimens op Cod from Experiments described by Dr. Fulton in 

 Twenty-second Report of the Board (for 1903). 



In the last Report Dr. Fulton, in his paper on " The Rate of Growth 

 of Fishes," described certain experiments on the influence of temperature 

 on the growth of cod and other fishes, experiments which were carried 

 out in tanks in the Board's Marine Laboratory at Aberdeen. Several of 

 the specimens which formed the subjects of these experiments were sent 

 to me by Dr. Fulton, and I have examined them with the following 

 results. Some of the specimens were from Tank I., in which the water 

 was of the natural temperature, not artificially heated. Dr. Fulton does 

 not give any dates in connection with these experiments, but I presume 

 that the codling were put into the tank in the autumn of 1903. They 

 were then from 12cm. to 15cm. long, or six inches and less. It is not 

 certain, but seems most probable, that they were then in their first year. 

 They were killed on August 4, 1904, and then sent to me. 



(1) Cod, Tank I. t 20'4cm. long. — The otolith in transverse section 

 shows two annual zones, i.e. a central opaque region, then a zone of more 

 transparent lamina?, then a zone of opaque lamina? again. The trans- 

 parent zone corresponds to the previous winter, and the specimen supports 

 the view that the opaque lamina? are deposited in summer, as they 

 extended almost to the edge, showing that they were being formed when 

 the fish was killed in August. The specimens were preserved in formaline, 

 and the skull bones were rather soft, but the layers of the otolith were 

 not obscured. In the scales also a winter zone was visible, the ninth to 

 twelfth rings being narrower and closer together. 



{2) 2Jf.'8cm. — In this also I made out two annual zones in the otolith, 

 though the winter zone was not quite so transparent. In the scales the 

 winter zone included rings 15 to 21 and was quite distinct, beyond it 

 were only seven or eight rings. 



These specimens, therefore, were in their second summer, according to 



