294 BULLETIN OF THE BXJKEAU OE FISHERIES 



aquaria, the second to include those acquired from marking experiments conducted 

 in the field. 



"Hintze (1888), who for some reason seldom is mentioned in reviews, contributed 

 the first bit of experimental evidence toward the determination of age by the scales. 

 He examined carp of known age and announced that the age of this species can be 

 determined quite accurately fi"oni the structure of the scales. At the same time Hintze 

 illustrated his method by diagrammatic sketches (reproduced by Walter, 1901) which 

 left no doubt that he referred to the annuli of scales. His sketches represented scales 

 of carp in their first, second, third, and fourth year. From these sketches it becomes 

 quite evident, however, that t.he author's interpretation of the scales was only partly 

 correct. His scale of the carp in its first summer correctly shows no age rings. The 

 scale of the carp in its second year shows two annuli of approximated and incompleted 

 circuli and three zones of relatively widely separated circuli. The scale of the 3-year 

 fish shows three annuli and four zones of growth, while that of the 4-year individual 

 shows four annuli and five broad zones. It is apparent that Hintze erred in his 

 interpretation of the scales of the 2-year fish. According to Walter (1901), Hintze's 

 difficulties were due to the fact that he did not examine carefully the differences 

 between the finer structures of normal and abnormal scales nor the characteristics of 

 a true annulus. His erroneous interpretation was due to the accessory annuli so 

 common on the scales of carp reared in ponds. 



In his prelicninary paper Hoffbauer (1898) describes very carefully the finer 

 structures of carp scales and presents two sketches. In a later paper (1900) the correct 

 method of age determination is more clearly elucidated and convincingly established 

 for carp 3 years of age and younger. Hoffbauer based his conclusions on his knowl- 

 edge of the life history of many carp bred and reared in ponds for commercial purposes. 

 To verify his assumptions supplejuental evidences were adduced from carp subjected 

 to experimental conditions. As Hoffbauer's works form the foundation upon which 

 all later scale studies have been built and his experimental evidences carry more 

 conviction than many subsequently produced, I shall review his work more in detail. 



Hoffbauer observed that the scales of the pond carp grev/ with the body. He 

 noticed that during the warm months of the year, when the fish grew most rapidly, 

 the marginal concentric ridges of the scales stood out in bold relief and were well 

 separated, but as v/inter approached they became more closely approximated and 

 began to diverge and break in the lateral fields. This condition at the margin per- 

 sisted throughout the winter when the carp were in a state of hibernation and all 

 body growth had ceased. With the resumption of growth in the spring the widely 

 separated circuli reappeared at the margin. The mark thus left on the scales he cor- 

 related with a retardation in growth and concluded that the number of such marks 

 gave a correct index to the age of the fish. He" successfully applied his hypothesis 

 to many pond carp whose ages and life histories were known. 



In order to verify this hypothesis the author subjected normal carp to various 

 environmental conditions. He considers, first, a carp in its third summer which had 

 been undernourished all its life and consequently had grown very slowly. He observed 

 that (1) the circuli were more closely approxunated and more uniform throughout the 

 entire scales than those of normal scales, (2) the annuli were less marked than in 

 normal scales but were recognizable by the usual characters of an annulus, (3) the 



