LIMNOLOGICAL INFLUENCE ON GIANT FRESHWATER PRAWN, Macrobrachium rosenbergii (DE MAN, 1879) PRODUCTION IN  SELECTED RESERVOIRS OF SRI LANKA 

Despite the umpteen stocking densities of Giant Freshwater Prawn (GFP) in Sri Lankan reservoirs, still there is a lacuna between the ultimate yield and the high stocking density. Lack  of scientific approaches has been identified as a major cause for this lower production. Therefore, the present study was conducted to understand the relationship between the production of GFP and various limnological and morphometric parameters in Sri Lankan reservoirs so that, it could provide a scientific insight to the production process. During the present study, which was conducted from March 2018 to August 2019, 48 reservoirs from five administrative districts (Hambanthota-11, Monaragala-24, Kurunegala-01,  Anuradhapura-11, Puttalam-12) were selected. Monthly temperature, pH, conductivity, Dissolved Oxygen (DO), Secchi Disk Depth (SDD), Chlorophyll-a content, and sediment  organic matter (OM) were collected as limnological parameters. Shoreline length and extent of  the littoral zone of each reservoir were also measured three times in regular intervals. Available  macrobenthos were identified using sediment samples from each reservoir. To calculate the  production of GFP in terms of Catch per Unit Effort (CPUE) catch data and information about gill net operations was collected with the help of village fisher’s organizations. Several GFP samples from each reservoir were collected to get length and weight measurements. Data calculations and analysis were done using Past version 3, Primer- E version 7, RStudio-1.2.5033 and Microsoft Excel 2016.  Principal Component Analysis (PCA) applied on limnological data resulted two clusters ordinating Kurunegala, Anuradhapura and Puttalam reservoirs into one cluster and the  Hambanthota and Monaragala reservoirs into the other. For further analysis of data  Hambanthota and Monaragala districts were considered as Southern region and the reservoirs of this region were considered as “S reservoirs” while the other three districts (Kurunegala, Anuradhapura and Puttalam) were considered as Northern region. Similarly, the reservoirs in those three districts were referred to as “N reservoirs”. N reservoirs has significantly higher (p  value