Studies On The Seasonal Variation In The Body Composition And Energy Density In Mystus Macropterus Bleeker

From December 2000 to October 2001, 148 fish of Mystus macropterus were collected in the Jialing River. Of which there were 31fishe in the winter, 32 in the spring, 33 in the spawning period, and 30 in the spent period and 22 in the Autumn. The body composition and energy density were measured in 10 specimens as a sample for each sex-season groups.The results were as follows:1. In the female, the protein content (16.2%), energy density (6.14 KJ/g), lipid content (5.84%), and dry mass content (26.7%) in the autumn were significantly higher than those in any other samples, the lipid content(2.39%)and the energy density (4.55 KJ/g) appeared the lowest In the winter.In the male the energy density (5.85 KJ/g) and protein content (16.34%) in the male appeared the highest in the autumn, and the lowest lipid content (1.31%), energy density (4.16 KJ/g), dry mass content (22.49%) appeared in the the spring.In the spring, the lipid content of males was lower than that of female significantly. And in any other samples, no significant difference of either body composition or energy density between the male and female was recorded.2. The highest gonadosomatic index (GSI) of either the male and female appeared in the spawning period (♀: 10.2, ♂ : 0.718), while the lowest of the females in the spent period(0.791) and that of males in the winter(0.183). The highest condition factor(5.33) of the male appeared in the spent period and the lowest in the spring (3.87), the highest of the females appeared in the spawning-period (5.64), and the lowest in the winter. The liversomatic index(LSI) in male and female followed the similar seasonal tendency, which the highest values appeared in the spawning-period(♀: 1.94; ♂ : 1.63) while the lowest in the spent period( ♀: 1.28; ♂ : 1.09).3. ' There was significantly linear relationship in each sample between energy density and either dry mass or lipid content, respectively. By analysis of covariance (ANCOVA) four models were developed for predicting energy density (E: KJ/g) with the dry mass (D: %B.W.) as the predictor. The first was for the female samples in the winter, spring, spent period and autumn i.e. non-spawning periods, as follows: E=-5.573+0.437D; the second for the female in the spawning period as: E=-0.605+0.250D; the third for the male samples in the non-spawning period as: E=-6.046+0.456D, and the fourth for the male sample in spawning period as: E=-3.64+0.366D. The discussion based on the result suggested that:1. Estimation of the energy density in the body of M. macropterus by using the dry mass content as predictor should be feasible, but the parameters in the predicting models for the different period of its reproductive cycle would be different.The parameter "a"(intercept) of the linear model for predicting the energy density of fish body reflected the relative levels of energy density for the different samples. The parameter "b"(slope) indicated the amount of energy density change by the change of per unit dry mass content. When there is no significant relationship between the relative ash content and dry mass content, the b value, which was decided by the ratio of the content of protein to lipid in dry mass, ranged from 0.236 to 0.395. While the correlation of the relative ash content with the dry mass content was negative significantly, the b value, as the result of the effect of ash content changed on the relative energy density in the dry mass, could be higher than 0.395...