Study On Age, Growth, Feeding Habits And Population Dynamics Of Ptychobarbus Dipogon In The Yarlung Tsangpo River

Ptychobarbus dipogon is one of the main economic fishes in Tibet area, only distributed in the upper and middle reaches of the Yarlung Tsangpo River and its tributaries. Under the pressure of growing demand for aquatic, P. dipogon is facing the threat of overfishing. We collected 956 samples from the Yarlung Tsangpo River monthly to study the aging materials, growth characteristics, feeding habits and population dynamics of P. dipogon. Collections were conducted through a combination of floating gillnets; set gillnets and trap nets from October 2008 to September 2009, April 2012 to July 2012 and March 2013. The main results were as follows:1. The study materials consisted of 229 samples.The typical annulus pattern with alternative wide zones and narrow zones was found on otolith and vertebrae. Annuli of otolith formed from March to June once a year. The maximum age observed was 14 and 13 of P. dipogon on otolith and vertebrae respectively. There was no significant difference between the results of them. The IAPE value of otolith and vertebrae is 1.43% and 4.28%, respectively. Otolith was more accurate and precise than vertebrae of P. dipogon for aging estimation.2. The range in standard length(SL) of P. dipogon was 78-569 mm, and body weight(BW) was 5.96-2241.1 g. Age determined from otolith and vertebrae ranged from three to twenty-four years for females, from three to thirteen years for males and from two to six years for undetermined. The SL and BW are usually linked by an allometic relationship: = 2.494 × 10-52.877 for females, = 2.790 × 10-52.856 for males, = 2.456 × 10-52.878 for undetermined. The von Bertalanffy growth functions were = 606.9(1- -0.114(+0.163)), = 2538.4(1- -0.114(+0.163))2.88 for females; = 493.6 1- -0.162 -0.018, = 1391.1(1- -0.162(-0.018))2.86 for males. The growth performance index of female and male were 4.6231 and 4.6010, respectively.3. The feeding intensity of P. dipogon was different in months, which indicated that it was high in April, October, November and December and very low from May to September. According to IRI, the main food was diatoms, macroinvertebrates, small intervebrates and organic detritus, while based on the W% and Ip%, macroinvertebrates and organic detritus was the main food, special Chironomid larvae and Hydropsychidae larvae. It was different with seasons, fish sizes and sexes for H’ and J.The dietary of P. dipogon was wide and no significiant difference among seasons, fish sizes and sexes.The feeding habits fited to the comformation of predatory device of P. dipogon.4. The first maturity size for females and males P. dipogon were 419 mm and 322 mm, and the first maturity age were 9.0 years and 6.1 years, respectively. Estimates of the total mortality rate(Z) were 0.66 year-1 for females and 0.65 year-1 for males. The natural mortality rates(M) were estimated as 0.10 year-1 and 0.24 year-1 for females and 0.14 year-1 and 0.33 year-1 for males using two empirical methods: tmax-based estimator and growth-based method. Under the current harvesting strategy, the stock of P. dipogon may be over-exploited when the M was low, while the male population may be in full exploitation in the Yarlung Zangpo River if the M was high. Though raise the age at first capture may be effective to conserve the P. dipogon stock, it may have effects on the income of local fishermen and on the biological invasion.