Otolith characteristics and age determination of an endemic Ptychobarbus dipogon (Regan, 1905) (Cyprinidae: Schizothoracinae) in the Yarlung Tsangpo River, Tibet |
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Authors: | Xiuqi Li Yifeng Chen Dekui He and Feng Chen |
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Institution: | (1) Laboratory of Biological Invasion and Adaptive Evolution, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China;(2) Graduate School of Chinese Academy of Sciences, Beijing, 100039, China; |
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Abstract: | We describe the microincrements, checks and annuli in the lapilli of the schizothoracine Ptychobarbus dipogon, an endemic species of the Tibetan plateau. We collected samples in the Yarlung Tsangpo River and its tributaries on a monthly
basis (from April 2004 to August 2006). We describe the shape features of the three pairs of otoliths and document the full
trajectory of lapillus development. We found that five to seven checks were clearly visible in the opaque zone of the first
annulus. The pattern of 21–23 daily growth increments within each check might be explained as a lunar-induced deposition.
We counted between 137 and 154 increments within the first annulus. Annuli appeared as a sequence of gradually declining increment
widths, whereas false rings were characterized by abrupt checks. Our oldest estimates were 23+years for males and 44+ for females. The time of annulus completion was clearly between March and April each year using monthly marginal increments
analysis. We consider the factors responsible for daily increment formation as an endogenous circadian rhythm. Environmental
information, such as strong sunlight and cold water temperatures in the Tibetan Plateau, could reinforce the endogenous daily
cycle. Our results provided important data addressing the ecology and population dynamics of P. dipogon. |
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