Growth and mortality parameters of Penaeus indicus from Sri Lanka (Negombo and Chilaw) caught between September 1982 and June 1986 are analysed on annual basis, based on length frequency data. The yield isopleths were then drawn.

The asymptotic length for different periods and areas varied from 20.5 - 24.0 cm total length and growth constant of the von Bertalanffy growth formula was found to-be between 1.5-1.8. The total mortality varied from 2.89-4.49. The mean natural mortalities for the whole period of study were 2.7 and 2.6 for Negombo and Chilaw respectively, whereas fishing mortality varied between 0.39-0.97 in Negombo and 0.30-1.86 in Chilaw.

From the relative yield isopleths drawn, an increase of fishing effort which results in a value of fishing mortality of 2.6 can be suggested with an increase of the minimum mesh size. As this is a multispecies fishery the optimum mesh size should be determined after finding a balance between the other commercially important shrimp species.