AGE AND GROWTH OF RHINOGOBIO CYLINDRICUS GÜNTHER IN THE UPPER REACHES OF THE YANGTZE RIVER

Rhinogobio cylindricus Günther is a cyprinid fish endemic to the upper reaches of the Yangtze River. The upper Yangtze River basin is experiencing critical changes to its ecosystem through multiple ecological threats in recent years, especially the impoundment of the Three Gorges Reservoir. R. cylindricus is a rheophilics species requiring diverse habitats to fulfill its life cycle. Otherwise the habitat once changed, life of R. cylindricus would be deeply affected. Therefore the study of age and growth, using scale, which is a basic and important aspect of fish biology and ecology, was essential to find out the growth characteristic of R. cylindricus after filling. The purpose of this study was to determine age structure and growth characteristics of R. cylindricus, and to propose reasonable measures to manage and protect this species. A total of 511 samples of R. cylindricus were collected from the upper reaches of the Yangtze River in Hejiang of Sichuan and Mudong of Chongqing from 2008 to 2010. The results showed that there were 6 age groups of our collected samples, and most individuals were 2—4 year-old accounting for about 95.7 percent of the total. According to the comparison of coefficient among linear function, exponential function, polynomial function and power function, and the relationship between body length (L) and scale radius (R) showed no significant difference between females and males, which could be expressed as L=51.28R+37.45 (r = 0.85, n = 397). And there was no significant difference between measured body length and back-calculated body length at each age group between females and males (t = 0.751, P > 0.05). Meanwhile, the relationship between body length (L) and body weight (W) showed no significant difference between females and males, and could be expressed as W= 8×10-6L3.099 (r = 0.97, n = 397). Von Bertalanffy growth function was Lt = 348.78 1-e-0.18 (t +1.15) and Wt = 603.17 1-e-0.18 (t +1.15)3.099. In addition, the age at the inflection point of body weight growth was 5.12 years old, when body length and body weight were 236.23 mm and 180.33 g, respectively. Besides, R. cylindricus was isometric growth and individual miniaturization. The exploitation of R. cylindricus in the upper of the Yangtze River was unreasonable, so we should take action to strictly ban catching in the future and strengthen scientific research on R. cylindricus to protect better.