Hatch date and early growth characteristics of different subspecies of Schizopygopsis younghusbandi Regan, 1905 in Xizang, China.
Liu Jiehong J, Chen Jie J, Huang Feng F, Chen Lin L et al.
Fish otolith microstructure is a fundamental aspect of fish ecology, providing insights into early-life history traits such as daily age, growth rates and hatch dates. To investigate variations in hatch dates and early growth characteristics among different subspecies, Schizopygopsis younghusbandi younghusbandi and Schizopygopsis younghusbandi shannaensis were collected from Xizang, China, during the spring and autumn of 2016 (S. y. younghusbandi) and 2020 (S. y. shannaensis). The formation of the first otolith increment in S. younghusbandi occurred on the second day post-hatching, with subsequent increments increasing at a rate of one per day, as confirmed through the analysis of otoliths from juveniles of known age. The hatch date differed between subspecies: S. y. shannaensis hatched earlier, beginning in January, while S. y. younghusbandi hatched from February onward. The growth rates also varied, with S. y. shannaensis exhibiting a higher rate than S. y. younghusbandi (total length [TL] = 0.096 D + 10.330, R2 = 0.690 for S. y. younghusbandi, TL = 0.118 D + 12.180, R2 = 0.886 for S. y. shannaensis). Increment width measurements of lapilli further supported the observation that S. y. shannaensis grows faster. Moreover, individuals collected in autumn demonstrated significantly greater growth than those collected in spring. These findings provide essential information for developing conservation strategies for S. younghusbandi and deepen our understanding of species adaptation to high-altitude riverine environments.