Abstract
Reservoirs in semi-arid southern India are critical for irrigation, fisheries, and local livelihoods, yet their ecological functioning remains insufficiently documented. In particular, the trophic linkages between plankton and fish assemblages are central to sustaining fisheries production. This study investigates the interactions between phytoplankton, zooplankton, and fish communities in the Sathanur Reservoir (12.2064° N, 78.8567°E.), Tamil Nadu, India, using seasonal field data on plankton density, fish abundance, and water quality parameters. Phytoplankton abundance, dominated by Chlorophyceae and Cyanophyceae, peaked during the monsoon months under high nutrient inputs, while zooplankton biomass was highest in the post-monsoon period, driven largely by copepods and cladocerans. Planktivorous fish (Catla, Labeo, and Cirrhinus spp.) exhibited significant positive correlations with zooplankton biomass, particularly with a one-month lag, suggesting strong bottom-up regulation. In contrast, piscivorous fishes were negatively associated with planktivore abundance, indicating trophic cascading. Redundancy analysis highlighted water level fluctuations, Secchi depth, and dissolved oxygen as key abiotic drivers influencing both plankton and fish assemblages. Variance partitioning showed that plankton variables independently explained a considerable fraction of fish community variation, beyond the effects of environmental parameters.
The study demonstrates that Sathanur Reservoir is governed by dynamic plankton–fish interactions modulated by hydrological seasonality. Incorporating plankton indicators into reservoir monitoring offers a robust approach to predict fish productivity and guide adaptive management for sustaining inland fisheries in southern India.
Keywords: plankton, interaction, reservoir, fish