S. costatum is chain forming one and it may occupy more space in the culture tank, the biomass (wet weight) of S. costatum was comparatively high. Similarly, S. costatum showed best performance in terms of growth in out-door culture, it was high enough to yield a large biomass in culture within a reasonable period of time. Since the S. costatum has chain forming nature which could increase the total biomass (Rekha et al., 2012). Salinity is an important factor, which profoundly influences the abundance, distribution, growth and composition of phytoplankton in the marine environment. There are several species of diatom, which showed higher rate of growth in different salinities. Diatoms from estuaries have the widest adaptability to any change salinity of the external medium (Williams, 1965). Growth rates of estuarine clones are not very much affected in media of wide salinities and the clones isolated from sea do not survive in lower salinities.