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Knowledge of fish age characteristics is necessary for stock assessments, and to develop management or conservation plans. Size is generally associated with age; however, there are variations in size at any particular age for most fish species making it difficult to estimate one from the other with precision.〔Helfman et al 1997〕 Therefore, researchers interested in determining a fish age look for structures which increase incrementally with age. The most commonly used techniques involve counting natural growth rings on the scales, otoliths, vertebrate, fin spines, eye lenses, teeth, or bones of the jaw, pectoral girdle, and opercular series.〔 Even reliable aging techniques may vary among species; often, several different bony structures are compared among a population in order to determine the most accurate method.〔Polat et al 2001〕〔Khan and Khan 2009〕 ==History== Aristotle (ca. 340 B.C.) may have been the first scientist to speculate on the use of hard parts of fishes to determine age, stating in ''Historica Animalium'' that “the age of a scaly fish may be told by the size and hardness of its scales.”〔Thompson 1910: Book VIII, Section 30〕 However, it wasn’t until the development of the microscope that more detailed studies were performed on the structure of scales.〔Jackson 2007〕 Antonie van Leeuwenhoek developed improved lenses which he went use in his creation of microscopes. He had a wide range of interests including the structure of fish scales from the European eel (''Anguilla anguilla'') and the burbot (''Lota lota''), species which were previously thought not to have scales.〔 He observed that the scales contained “circular lines” and that each scale had the same number of these lines, and correctly inferred that the number of lines correlated to the age of the fish. He also correctly associated the darker areas of scale growth to the season of slowed growth, a characteristic he had previously observed in tree trunks. Leeuwenhoek’s work went widely undiscovered by fisheries researchers, and the discovery of fish aging structures is widely credited to Hans Hederström (e.g., Ricker 1975). Hederström examined the vertebrae of pike (''Esox lucius'') and concluded that each contained growth rings which could then be used to determine the fish’s age.〔 In 1859, Robert Bell reported that one could use these growth rings to reliably determine the age of all fish after examination of sucker (''Catastomus sp.'') vertebrae and yellow perch (''Perca flavescens'') scales that he raised in a pond for two years showed “two rings or circles.” In 1898, more than 200 years after Leewenhoek’s original insights of scale age structure, this subject was given a thorough review by C. Hoffbauer.〔 Hoffbauer studied commercially grown carp scale growth patterns throughout the year. He noted that during the season of growth, the concentric rings were easily discernible and widely spaced; however, as growth slowed and ceased during the winter months the rings were very compact then resumed normal spacing as the growth season began again. His work convinced other researchers that these aging techniques could be used on marine species. Shortly after Hoffbauer's findings were published, structures other than scales were examined for utility of aging fish. Johannes Reibisch, working for the Commission of Scientific Investigation of German Seas at Kiel, attempted to use Hoffbauer’s techniques to age plaice (''Plueronectes platessa'') but found it difficult to accurately discern annuli. He decided to study a different structure and in 1899 he published the first procedures using otoliths as an aging structure.〔 A fellow scientist also with the German Commission at Kiel, Friedriche Heincke, also frustrated with difficult scale annuli, further studied other structures to age fish. He discovered annuli in the vertebrae, opercula, and pectoral girdle and published his findings in Heicke 1905. The works of Hoffbauer, Reibisch, and Heinke are most often cited as establishing scales, otoliths, and bony structures as viable aging structures. Further, Tereshenko (1913) is credited as the first to use cleithra aging techniques on roach; and Holtzmeyer (1924) with using fin rays to age sturgeon. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Estimating the age of fish」の詳細全文を読む スポンサード リンク
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