The study was conducted to evaluate the population structure, morphometric relationships and growth in a commercial important bivalve species, Meretrix casta, collected from May 2010 to April 2011, from the intertidal region of the Sonmiani Bay, Balochistan, Pakistan. Some 445 males and 451 females of Meretrix casta measuring 10-77 and 14- 77mm and weighing 0.2-72.5 g and 0.7-96 g respectively were studies. The overall sex ratio was slightly in favour of females (50.33) and 49.67 were males 1.151. 2 Allometric variations in various parameters were calculated with empirical equation W = aLb after transferring on logarithms. The relationship between length versus meat of the shell was stronger interpreted from R2 = 0.776 and weak relationship in wet tissue weight and shell height R2 =0.054 was estimated. The growth was estimated with the von Bertalanffy growth model estimate L∞ = 72.45mm, growth coefficient K = 0.960 year-1 , score 0.408.
