Characteritics Of Otolith And Growth On Larval And Juvenile Of The Four Major Chinese Carps From Jiujiang Section Of The Yangtze River

The four major Chinese carps, black carp(Mylopharyngodon piceus), grass carp (Clenopharyngodon itlellus), silver carp (Hypophthalmichthys molitri), and bighead(Aristichthys nobilis) are famous cultivated species in China, and also are important fish resources in the Yangtze River, with great economic value. In this dissertation, the otolith was examined and analyzed to describe its morphology and microstructure, determine the age, hatching date and spawning date in larval and juvenile of the four major Chinese carps. The growth of otolith, body length and weight were also studied. The wild larvae used in the study were collected from Ruichang section of the Yangtze River in June 2010; the wild juveniles were collected from Hukou section of the Yangtze River from July to August 2009. The main results are as follows:1. Most of the appearances of sagittae and lapillus in larvaes were round-shape, fews were oval-shape. However the appearances of three kinds of ototlith in juveniles were very different. The nucleus, primordium, increments and checks were observed on otoliths, and two primordiums were observed in few abnormal otoliths. The increment clarity of otolith in wild larvae was hardly examined or just subtile. The percentages of lapillus and sagittae with clear increments were respectively less than 25% and 5% in larval black carp, grass carp and silver carp. However increments on lapillus in juvenile of the four domestic fishes were all clear. The poor clarity of larvaes was probably related to the water-temperature in the Yangtze River was relatively stable; especially the diel water-temperature fluctuations were very-low.2. According to counting and analyzing the increments on lapillus of larvaes collecting in three times, average ages of 46 larval black carps were 9.20±1.36d, most of the distribution was 8-9d. Average ages of 315 larval grass carps were 8.97±0.73d; most of the distribution was 9d. Average ages of 223 larval silver carps were 8.97±0.73d; most of the distribution was 9d. Hatching dates of larvaes were all from May 25 to June 17, which were back-calculated based on the collecting dates and ages, spawning dates of mature fishes were all from May 23 to June 15. Spawning sites of mature fishes were probably located in Xinmatou to Yichang section of the Yangtze River, and the main section was Shishou to Haoxue. Average ages of 23 juvenile black carps were 52.4±5.6d; most of the distribution was 45-55d. Average ages of 111 juvenile grass carps were 57.1±10.6d; most of the distribution was 45-65d. Average ages of 73 juvenile silver carps were 49.8±4.7d with mass distribution. Average ages of 70 juvenile bigheads were 57.5±7.1d; most of the distribution was 50-60d. Back-calculating based on the collecting dates and ages, Hatching dates of juvenile black carps were May 28 to June 19, juvenile grass carps were May 22 to July 7, juvenile silver carps were May 30 to July 11, juvenile bigheads were May 24 to July 2. Spawning dates of larvaes and juveniles in this paper were distinctly delayed than the history datas. We infered that the temperature of water came from the Three Gorges was too low may be the main reason. The spawning dates were delayed by this negative effect.3. Regression analysis between total length and daily age of larvaes shows that, black carps and grass carps collected in June 6 were in a linear correlation, while every batch of silver carps were in a linear correlation, but the two batches collected in June 16 and June 24 had a small correlative coefficient. The results shows that larval of the four domestic fishes living in the Yangtze River differed large in growth with each other. Regression analysis shows that, daily age of juveniles were in a linear correlation with body length and weigh, body length were in a power correlation with body weigh.4. Regression analysis shows that, long otolith diameter of sagittae and lapillus of larvaes was all in a linear correlation with the daily age and total length in every batch. Short radius of lapillus of juveniles was all in a linear correlation with the daily age, as well as body length and weigh.