ANNULI CHARACTERISTICS OF THE DIFFERENT AGEINGMATERIALS OF GYMNOCYPRIS PRZEWALSKII PRZEWALSKII( KESSLER)

Gymnocypris przewalskii przewalskii (Kessler) is the only economically important local aquatic animal in the Qinghai Lake,the biggest inland saltwater at the altitude of 3195 meters above the sea lever in China.Because the lake is in the zone of high elevation and severe cold,and the water temperature is rather low,the food organisms in the lake are in paucity.Thus,G.przewalskii przewalskii grows very slowly,and has a small brood amount as well as low survive rate. Since the exploration in 1958,its stock abundance decreased rapidly because of imperfect management and over2large intensity of fishing.At present,G.przewalskii przewalskii is in the danger of depletion,and its depletion will severely destroy the ecological balance of the"coexistence of fishes and birds",resulting in the collapse of the whole ecological system in the Qinghai Lake. Therefore,the saving of G.przewalskii przewalskii is especially important ,and a series of researches on the biology and resources assessment were carried out from 2002.In this paper,the annuli characteristics of four kinds of ageing materials of G.przewalskii przewalskii have been described and compared in their usage in age determination.Four hundred and fifty samples of G. przewalskii przewalskii of different size were collected from the Qinghai Lake and the rivers around the lake fromMay 2002 to February 2003.The ages were identified though the materials of anal scales,otoliths,dorsal fin spines and vertebrae,respectively.The anal scales and vertebrae could be observed directly in transmitted light or reflected light after being washed and dipped in the KOH solution of 0.5 % concentration,but the otoliths and dorsal fin spines should be sectioned by sand paper to the slices.The lapillus and dorsal fin spine were sectioned to 0.1 to 0.2mm thick slices and 0.5 to 1.0mm thick slices respectively,and the asteriscus only needed a little section.The sectioned otoliths and dorsal fin spines could be made more transparent by dipping in dimethylbenzene for a while then airproofed by neutral gumon the glass slices before being observed in the dissector or for long-term storage.The results showed that the ages of G. przewalskii przewalskii can be identified though the annuli characteristics of the anal scales,otoliths,dorsal fin spines and vertebrae.The annuli characteristics on the anal scales have two types.One is the type that has zones of widely and closely spaced circuli which can form ridges,and the outer edges of the ridges are annuli.The other has no evident zones of widely and closely spaced circuli,but possesses some obvious circles which are annuli at interval on the anal scales.It is not easy to identify the ages because of the irregulation of annuli on the anal scales, and the difficulty will increase when there are some disturbances of fry checks and false rings,which will decrease the accuracy of aging.The three pairs of otoliths of G.przewalskii przewalskii are all relatively big ,among which lapillus look like the shape of horse foot,the shape of asteriscus is circular slice with concave center,and the shape of sagitta is long stick.Both lapillus and as- teriscus can be used for ageing,coming to an agreement of 88%.The error of the annuli readings has no evident increase with the increase of the ages,and coming an agreement of 100% where the error is±1 annuli.Sagitta is not suitable for ageing because of its fragility.The annuli characteristics of the sectioned lapillus are more clear than those of the sectioned asteriscus,thus the accuracy of ageing though the lapillus is relatively higher.The sectioned asteriscus is very convenient to operate and this ageing method can be used when there are many samples to determine ages.Observed in transmitted light,wide opaque zones and lose translucent zones are in alternatives arrangement on the sectioned otoliths,dorsal fin spines and vertebrae.The boundaries between the translucent zones and the outer edges of the opaque zones are the annuli.The wide zones and close zones are just reversed when observed in reflected light.The observed results showed that the characteristics of the dorsal fin spines are relatively clearer than other ageing materials.For the vertebrae,the annuli fromone to three close to the center and the annuli close to the outer edge are usually in illegibility.The comparisons of characteristics and ageing results showed that the interpretability of the four kinds of ageing materials is sectioned dorsal fin spine>sectioned lapillus>analscale>vertebra.Sectioned dorsal fin spine is a better ageing material of the fish less than eight years.As for the fish older than eight years,sectioned lapillus is the relatively reliable ageing material that has more annuli readings than anal scale,dorsal fin spine and vertebra.