Relationship between the growth of juvenile masu salmon (Oncorhynchus masou) and the circuli number, scale and central plate radii
1996
Kato, T. (National Research Inst. of Aquaculture, Tamaki, Mie (Japan))
In order to clarify the relationship between scale formation and growth of masu salmon, the number of scale circuli, and the radii of scales and of the central plates were examined. Although the radius of scales increased with the growth of individuals, the size of the central plate remained unchanged as individuals grew, indicating that the central plate, once formed, does not expand nor contract in the course of the growth of scales. Body lengths at 20 months of age varied widely, from 9.6 cm to 19.5 cm, even among a group of juveniles reared in the same tank, and the number of circuli showed a large variation between individuals ranging from 18 to 32. Such variations were also observed among individuals with similar body lengths. These results reveal that, even among juveniles of the same age and of a similar size reared under the same conditions, the number of scale circuli are not necessarily identical. The length of fish at which scales began to be formed varied with the water temperature at which fish were reared. The higher the temperature the smaller the fish were at the initiation of scale formation. From the finding that large individuals had larger central plates than small individuals, it suggests that scales begin to be formed at a stage when larger body length had already been attained in the larger fish than in small fish. When the number of circuli and the scale radii were compared between fish of the same age and similar size reared at different temperatures, it was found that both the circuli number and the scale radius increased with temperature
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