Population dynamics of two sympatric native and exotic cichlids in a tropical microtidal estuary, India

Population dynamics of two sympatric cichlids, the native Etroplus suratensis and the alien Oreochromis mossambicus, were determined from the Vembanad Lake, the largest estuarine system of southern peninsular India. Based on annual length-frequency data, the results revealed that E. suratensis has a higher asymptotic length (L∞) (302 mm vs. 262mm), but a lower growth constant (K) (0.68 year-1 vs. 1.1 year-1) than O. mossambicus, suggesting the faster growth rate of the alien species. Natural mortality (M) rates recorded for E. suratensis (0.69 year-1) indicate lower levels of predation and other natural stressors in the lake. The exploitation ratio (E) was estimated to be 0.83 for E. suratensis and 0.78 for O. mossambicus, both values greater than the predicted optimum and suggestive of overexploitation. Our study provides the first information on the demography of wild E. suratensis, which would help inform future management strategies in the Vembanad Lake.