3 resultados para Age-dependency ratio

em Chinese Academy of Sciences Institutional Repositories Grid Portal


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Age, growth, and reproduction of the bitterling, Paracheilognathus imberbis (Gunther), in Niushan Lake were studied between 1998 and 1999. Annuli on the scales were clear and could be used as valid indicators of age. The population of the fish comprised only one age group. The growth rate of males was markedly greater than that of females. The fish were multiple spawners, reaching maturity in the second year. Minimum size for males at maturity was 32.9 mm in total length and 0.30 g in weight; for females, the minima were 41.0 mm and 0.73 g. During the breeding season, both sexes exhibited secondary sex characteristics, and the ratio of males to females was 1: 1.04 (n = 104). The size of mature eggs averaged 3.12 mm in length by 1.03 mm. in width. Fecundity per female for one age group ranged from 38 to 189 eggs, with an average of 93 eggs (n = 80).

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Based on the isospin- and momentum-dependent transport model IBUU04, the transverse momentum distributions of the free neutron-proton ratio in the Sn-132+(124) Sn reaction system at mid-central collisions with beam energies of 400/A MeV, 600/A MeV and 800/A MeV are studied by using two different symmetry energies. It is found that the free neutron-proton ratio as a function of the transverse momentum at the mid-rapidity is very sensitive to the density dependency of the symmetry energy especially at incident energies around 400/AMeV.

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Laboratory studies have shown that Antarctic krill (Euphausia superba) shrink if maintained in conditions of low food availability. Recent studies have also demonstrated that E. superba individuals may be shrinking in the field during winter. If krill shrink during the winter, conclusions reached by length-frequency analysis may be unreliable because smaller animals may not necessarily be younger animals. In this study, the correlation between the body-length and the crystalline cone number of the compound eye was examined. Samples collected in the late summer show an apparent linear relationship between crystalline cone number and body-length. From a laboratory population, it appears that when krill shrink the crystalline cone number remains relatively unchanged. If crystalline cone number is little affected by shrinking, then the crystalline cone number may be a more reliable indicator of age than body-length alone. The ratio of crystalline cone number to body-length offers a method for detecting the effect of shrinking in natural populations of krill. On the basis of the crystalline cone number count, it appears from a field collection in early spring that E. superba do shrink during winter.