Between April 1992 and March 1993, intersexual plasticity in aspects of the biology of the mudskipper, Periophthalmus barbarus was studied. Sex was differentiated on the basis of the genital papillae, it was broader in females than males. Sexually active females were slightly heavier than similarly-sized males. Sex ratio was strongly female-biased.length-weight relationship of the sexes was isometric. There was no significant difference in the feeding intensity of both sexes; uniformity was also apparent in diet breadth. There was no named sex-based difference in hepatosometic index but condition index was higher in males than females. The uniformity in intersexual plasticity of P. barbarus is consequent upon homogeneity of the mangrove ecosystem, which can only be altered anthropogenically.