AGE, GROWTH AND REPRODUCTION OF ZACCO PLATYPUS IN THE HUISHUI STREAM

Identifying the life history of fishes is the basis for scientifically protecting fish species diversity and reasonably managing fishery resources. In this study, age, growth and reproduction of Zacco platypus in the Huishui Stream were examined using 352 specimens collected monthly from May 2009 to April 2010. Sex ratio was 0.49∶1 (female: male), which was significantly different from 1∶1 by χ2 test. Using scales for age determination, the largest longevities were both age 3 for females and males. Based on the monthly changes in marginal increment ratio (MIR), annuli on scales were formed during March, which was associated with the relatively low water temperature constraining the somatic growth in winter. The relationships between total length (L) and weight (W) were W = 5×10–6L3.15 for females and W = 7×10–6L3.09 for males. Due to no significant difference discovered by ANCOVA between sexes, L–W relationship was combined as W = 6×10–6L3.10 for both sexes. L–R (scale radius) equations were L = 29.58R + 38.84 for females and L = 33.17R + 34.99 for males, and significant difference was observed between them. The back-calculated total lengths (BCL) at age 2 were (82.59 ± 9.77) mm for females and (84.65 ± 11.77) mm for males, and those age 3 were 120.56 mm (only one specimen) for females and (94.97± 9.85) mm for males. According to t-test result, no significant difference was observed in BCL at age 2 between the two sexes. The monthly changes in gonado-somatic index (GSI) suggested that Z. platypus spawned from April through July, which was almost synchronous with local flooding period, because flood could bring sufficient food for larva and decrease the risk that larva were preyed by predators. Fifty percentage of individuals got the first maturity at age 2, when the average total lengths were 98.22 mm for females and 105.69 mm for males. In terms of the number of the occytes with vitellinogenic granules from mature ovaries, the absolute fecundity (AF) and relative fecundity (RF) were (758 ± 362) eggs and (77.38 ± 22.15) egg/g. Comparing the observed results in this study with those in limited others, the age structure of the population of Z. platypus in the Huishui Stream was similar with that in the Puxi Stream but not with that in Beijing region. In addition, somatic growth of Z. platypus was faster in the Huishui Stream than that in the Puxi Stream, which was suggested by their difference in the back-calculated length at each age. These variations in the life history among different populations of Z. platypus were possibly associated with the spatial heterogeneity in ecological environment. However, the future studies should be operated to identify how this species trades off among different life-history variables (i.e., age and body size at sexual maturity, longevity, fecundity, and somatic growth rate) and how environment influences the trade-off in life history.