STUDIES ON AGE DETERMINATION AND GROWTH CHARACTERISTICS OF GYMNOCYPRIS CUOENSIS

The characteristics of three kinds of age determination materials, otoliths scales and dorsal fin spines from Gymnocypris cuoensis had been described and compared in their using in age determination. Regressive body length was used to fix the Von Bertalanffy function. Otoliths are good materials in age determination, which have relatively clear annuli and are unlikely to lose annuli because of absorption or erosion. In scales of most fish elder than eight years, the annuli became undistinguishing. It was difficult in most of the cases to distinguish true annuli from pseudoannuli. Dorsal fin spines in fish elder than seven years were not accurate either because of their irregulation in annuli deposit or their lost of annuli. This research shows that scales are as accurate as otolith in determining the age of fish below eight years. Dorsal fin spines showed the same age as otoliths and scales when fish was younger than seven years old. Dorsal fin spines tended to lose annuli at a greater extent in the elder fish than those in otoliths and even scales. The largest fish of 29 years old was identified with otolith while 24 and 22 years old with scale and dorsal fin spine respectively. There were several conditions in the sections of otolith that may cause confusion when counting annuli. First of which, there existed four light bands or so between two adjacent annuli. Second, several light band could be found in the nucleus dark zone. The third one, in the dorsal direction of some section sometimes one could find that two annuli converge into one band. Puzzling conditions also existed in scale and dorsal fin spine sections, mostly because of the pseudoannuli and undistinguishing of annuli. The growth of G. cuoensis described by Von Bertalanffy growth models is well fitted with the data from otoliths and scales, but not so good with the data from dorsal fin spines. The growth can be described with the function of Lt=639.7070×[1-e-0.0291×(t+4.6745)],with statistic r2=0.9864 for otolith. Weight function is Wt=2750.8718×[1-e-0.0291×(t+4.6745)]2.4792. For scale, Lt=571.1190×[1-e-0.0354×(t+4.6743)],r2=0.9761;Wt=2076.6268×[1-e-0.0354×(t+4.6743)]2.4792. Both otolith and scale described the growth of G. cuoensis well, dorsal fin spine fills to do so, for L∝=1759.3990g,K=0.0080.