Giant freshwater prawn and finfish distribution in microhabitats in irrigation reservoirs of Sri Lanka

Abstract

This investigation examined spatial distribution patterns of GFP (M. rosenbergii) and associated ichthyofauna across distinct microhabitats within irrigation reservoirs utilised for CBF in Sri Lanka. Methodology employed stratified random sampling across 185 sampling stations distributed among 5 reservoirs. Limnological parameters were quantified in situ, and fish and prawn populations were sampled via overnight deployments of multi-mesh gillnets (25–100 mm mesh sizes). Statistical analysis through PERMANOVA revealed significant spatial heterogeneity in species assemblages across microhabitat types (p<0.05). Wood log (WL) habitats exhibited significantly different community structures compared to gravel and rocky substrates (GR), vegetation-associated zones (VA), and pits and channels (PC). Notably, open water (OP) microhabitats demonstrated no statistically significant differences in species composition when compared with other microhabitat types. Principal species contributing to microhabitat-specific community differentiation included members of the family Channidae and various size classes of cyprinid species. M. rosenbergii was identified as a significant contributor to dissimilarities between GR and VA habitats. These findings demonstrate the ecological importance of microhabitat heterogeneity in structuring aquatic communities and provide empirical evidence to be considered in the management of CBF in tropical reservoir ecosystems.