Bin Huo

Reproductive biology of Oxygymnocypris stewartii in the Yarlung Zangbo River in Tibet, China

We determined the gonadal histology, reproductive characteristics and implications for management of Oxygymnocypris stewartii from individuals collected in the Yarlung Zangbo River. Based on the analyses of gonad development and the size distribution of oocytes, O. stewartii spawns just once each year. Peak spawning occurred between late March and early April, when water temperature exceeded 5°C. The standard lengths and the ages at 50xa0% maturity for males and females were 273xa0mm and 357xa0mm, and 5.1xa0year and 7.3xa0years, respectively. The mean fecundity of 34211 and mean relative fecundity of 25.4 eggs per gram of fish body weight suggest that O. stewartii might be especially vulnerable to exploitation.

Reproductive biology of Schizothorax waltoni (cyprinidae: schizothoracinae) in the yarlung zangbo river in Tibet, China

The reproductive biology of Schizothorax waltoni (Cyprinidae: Schizothoracinae) was studied by examining 1,145 individuals collected between August 2008 and August 2009 in the Yarlung Zangbo River, Tibet. The population had a significantly higher proportion of females than males (χ2 test, pu2009<u20090.05). Using a logistic regression, it was determined that the standard lengths at 50xa0% maturity were 369xa0mm for males and 479xa0mm for females; the ages at 50xa0% maturity were 10.2xa0years for males and 13.5xa0years for females. Based on the monthly proportions of macroscopic gonadal maturity stages and monthly variations in the gonadosomatic index, S. waltoni spawned over a short period, from March to April with a peak in March According to the size distribution of oocytes, S. waltoni appeared to show a high degree of spawning synchronicity. The fecundity of S. waltoni increased linearly with the standard length, body weight and ovary weight, but had no significant correlation with age. The mean fecundity of 21693 and mean relative fecundity of 13.4 eggs per gram of fish body weight suggest that S. waltoni might be especially vulnerable to exploitation.

Age and growth of Schizothorax waltoni (Cyprinidae: Schizothoracinae) in the Yarlung Tsangpo river, China

ABSTRACT To better understand the biology of Schizothorax waltoni, the age structure and growth characteristics of S. waltoni were examined. The standard length (SL) range was 41–642u2005mm and the body weight (BW) range was 1.1–3788.1u2005g. Otoliths continually grew with increasing SL and increasing age, but asymmetrically over time. One annulus was formed each year, between April and July. Estimated age range was 4–37u2005yr for males, 4–40u2005yr for females, and 1–9u2005yr for those of undetermined sex. The SL–BW relationship was described as BWu2009=u20091.365u2009×u200910−5 SL2.984 for females, BWu2009=u20091.238u2009×u200910−5 SL2.999 for males, and BWu2009=u20093.664u2009×u200910−5 SL2.800 for undetermined specimens. The von Bertalanffy function was used to model the observed length-at-age data as Ltu2009=u2009644.3 {1u2009−u2009exp [−0.084(tu2009−u20090.247)]} for females, and Ltu2009=u2009586.2 {1u2009−u2009exp [−0.084(tu2009+u20092.250)]} for males. Females grew faster than males. Knowledge of this species’ characteristics of slow growth and a long life will be useful for establishing reasonable management practices for its conservation.

Reproductive biology of Schizopygopsis younghusbandi Regan 1905 (Cyprinidae: Schizothoracinae) in the middle reaches of Yarlung Tsangpo River, China

The reproductive biology of Schizopygopsis younghusbandi (Cyprinidae: Schizothoracinae) was studied by 719 individuals that collected from August 2008 to August 2009 in the middle reaches of Yarlung Tsangpo River, China. We coupled monthly variations of the gonadosomatic index (GSI), monthly proportions of the macroscopic maturity stages with size distribution of oocytes to evaluate spawning seasons. Taken as a set, these results indicated that S. younghusband i spawned from March to April with high degree of the spawning synchronicity. The standard lengths and the ages at 50% maturity for male were 222 mm and 4.4 year, and 308 mm and 7.0 year for female. In addition, the estimated mean fecundity and mean relative fecundity were 18682 and 57.8 eggs per g body weight. The fecundity of S. younghusbandi increased linearly with increasing of standard length and body weight. This study provides details about the S. younghusbandi reproduction suggesting that may be this species is vulnerable to exploitation in the middle reaches of Yarlung Tsangpo River.

Stock assessment and management implications of an endemic fish, Oxygymnocypris stewartii, in the Yarlung Zangbo River in Tibet, China

BackgroundOxygymnocypris stewartii is an endemic species only inhabiting the middle and upper reaches of the Yarlung Zangbo River and its tributaries at altitudes above 3600 m in the Qinghai-Tibet Plateau and has suffered a continuous decline of population size owing to anthropogenic disturbance. However, little is known about the stock status of this species and how to protect it. In this study, we evaluated the population status of O. stewartii and investigated two management policies including the minimum age limits and seasonal closure in the Yarlung Zangbo River.ResultsEstimates of the total mortality rate were 0.35 year−1 for females and 0.65 year−1 for males. The natural mortality rates were estimated as 0.10 and 0.22 year−1 for females and 0.12 and 0.29 year−1 for males using two empirical methods. The O. stewartii population may be in near full exploitation under the current harvesting strategy in the Yarlung Zangbo River, with a high chance of recruitment failure in the future. Although both minimum age limits and seasonal closure could be effective measures to conserve the O. stewartii stock, it was proposed that a seasonal closure was implemented each year from September to December according to the complexity of the application and the effects on the income of local fishermen and on the biological invasion.ConclusionsThe stock of O. stewartii may be in near full exploitation under the current harvesting strategy, with a high chance of recruitment failure in the future. Our results indicated that the imposition of the seasonal closure from September to December might be the effective measure to conserve the O. stewartii population.