Seventy eight wild Wallago attu and eighty Sperata sarwari of different body sizes were collected for analysis of body composition, morphometric parameters and elemental concentration. Each sampled was measured, weighed, dried and powdered for the analysis of water content, ash content, fat content and protein content. It was observed that highly significant inverse correlations exist between percent water content and percent ash content (wet weight), percent fat content (wet weight) and percent protein content (wet weight) in both species. In Wallago attu, there was no effect of wet body weight and total body length on percent water contents but positive influence on percent ash contents (wet weight), percent fat contents (wet weight), percent protein contents (wet weight), percent ash free matter (wet weight and dry weight), percent fat free matter (wet weight) and percent protein free matter (wet weight and dry weight). In case of Sperata sarwari, wet body weight and total body length have positive influence on percent water contents, percent fat contents (wet weight), percent protein free matter (wet weight and dry weight) and negative influence on percent ash contents (wet weight), percent protein contents (wet weight), percent ash free matter (wet weight and dry weight) and percent fat free matter (wet weight). Condition factor has a highly significant positive correlation with percent fat content (wet weight) in both species. When comparative study was done, it was found that there were highly significant differences between these two species in ash contents (wet and dry weight), protein contents (dry weight), ash free matter contents (dry weight), fat free matter (wet weight) and protein free matter (wet and dry weight). There was no significant effect of sex on body constituents in both species. The results also indicated that the proximate composition of the Wallago attu and Sperata sarwari depend on season. It was found that body constituents varied in different months of the year. The predictive equations can be used to estimate values of body composition with a fair amount of accuracy for both species. Flame Atomic Spectrometry was used as an analytical tool for analysis of trace metal concentration in relation to body size. In Wallago attu, it was observed that the metals i.e. Cd, Co, Fe and Cu were found to increase isometrically while Zn, Ni and Pb showed negative allometry with increasing body weight and total length. In Sperata2 sarwari, Cd, Co, Fe and Zn were found to increase isometrically while Ni, Cu and Pb showed negative allometric growth with body weight and total length. In both species, there were not significant differences in elemental concentration with relation to sex. The effect of season on elemental concentration was analyzed by using the ANOVA. Significant differences were observed in case of copper, zinc and lead concentrations in Wallago attu while zinc and nickel concentrations in Sperata sarwari. Wet body weight of both the species was not consistent with the cube law and showed positive allometry. The regression slope was W = 0.001698 L 3.27 for W. attu and W = 0.001698 L 3.28 for S. sarwari. The values of the slope b are significantly higher than b = 3.0, which shows that the weight grows more rapidly as compared to the cube of the length. Regression analysis showed that all the morphometric parameters except for eye diameter, mandible barbells length in W. attu and eye diameter, caudal fin length, nasal barbells length, maxillary barbells length and mandible barbells length in S. sarwari showed isometric growth with relation to wet body weight and total length of the fish. While the regression coefficient of all the fins weight except for dorsal fin in W. attu and caudal fin in S. sarwari showed positive allometric growth with body size. In internal morphometric studies, except for air bladder weight and gonads weight all the parameters showed negative allometric growth with relation to wet body weight and total length.