| Xenophysogobio boulengeri is an endemic fish to the upper Yangtze River, and mainly inhabits the main channel. From October 2001 to September 2002, 1613 specimens collected from Luzhou to Yibin sections in the lower Jinsha River were used for studies on aging, age structure, growth, reproduction and other biological characters of the fish. The following are the main results:1. Scales could be used for aging the fish efficiently. Annuli were formed mainly by sparseness-denseness or fragmentation in the scale with occasional incisions in its side -rear areas. No juvenile or spawning checks were observed in the scale. Aging results of scales corresponded with that of vertebra in 80.00% (n=155). The annuli are laid down mainly from March to April and the ratios of the scales with new annulus increases from 39.66% to 98.46%.2. The commercial catches consisted of five age groups (age 1 to age 5) and individuals of age 1 to 3 groups were dominant (occupying more than 90 % of total capture). The body length changed from 51mm to 146mm with an average of 89mm. The mesh sizes of drifting net were from 1.8cm to 2.4cm and individuals which the body lengths were more than 90mm were totally selected by the fishing methods. About 22.05 % individuals of age 1 group reached the length selection standard of the net. No significant differences in growth were detected between the females and males. Male to female ratio was about 1 to 1.3. The relationship between body length (L, mm) and the diameter of the scale (R, mm) was L=29.742+71.735R (r2=0.805, n=450). Weight (W, g) - length relationship was W=1×10-5×L3.1136 (r2=0.9718, n=1187). The Von Bertalanffy growth equations were L,= 195.51 (l-e-0.1611 (t+1.51) and Wt=136.08(1-e-0.1611 (t+151)) 3.1136 for the length and weight respectively. The inflection point of body weight was about 5.54 years.4. Secondary sexuality. During reproduction periods, some white nuptial organs were visible on cheek, orbit, opercular, head and lateral scales in males. However, no same organs could be checked in females.5. Spawning stocks involved all five age groups and about 90 % individuals were two to three years old. 25.0 % females matured at one year, 87.5 % at two years old, while about 40.0 % males matured at one year, 89.2 % at two years old. All females and males of three years old reached maturity. The minim mature female was 84 mm in length9.4g in weigh with a 0.25g ovary of stage IV. The minim mature male was 80 mm in length 8.8 g in weigh6. The ovary maintained in stage II in winter began to develop in March and reached maturity in May. Individuals with the IV-V stage ovaries could be found from May to September. Value of gonadosomatic index (GSI) increased in March, approached a peak in June and decreased to bottom in October till the beginning of the next March. The spawning activities of the fish could last from May to September.7. In a stage VI ovary, there were oocytes both in phase 3 (60.87 % in quantities and 39.13% in occupied areas) and phase 4 (39.04 % in quantities and 60.96% in occupied areas). Two peaks in the frequency distribution figure of egg sizes showed that the fish could spawn twice within a reproductive period. The fertilized eggs were drifted in the flow.8. The absolute fecundity (F) ranged from 1112 to 15805 eggs with an average of 5791 (±2797.64 SD). The relative fecundity to weight (Fw) ranged from 85.54 to 634.31 with an average of 282.49 (±93.75 SD), and that to length (FL) ranged from 12.09 to 131.65 with an average of 53.55 (±22.64 SD). The results of correlation and regressions analysis indicated that fecundity of the fish could be fluctuated primarily by variations of goand mass, GSI, body length, and weight. |
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