Factors related to nesting sites of Oreochromis niloticus (Cichlidae) in irrigation reservoirs, Sri Lanka

Abstract

The nesting sites of Oreochromis niloticus (Linnaeus 1758) were studied in 10 irrigation reservoirs of Sri Lanka from April 2014 to April 2016 to understand the influencing factors. The optimal nesting depth and nest diameter varied across reservoirs. Nest density (ND) was negatively related to slope of the littoral area (in degrees) according to ND = -0.070 Slope + 0.536 (R2 = 0.415) and positively to water turbidity (Turb in NTU) according to ND = 0.033 Turb + 0.083 (R2 = 0.598). The optimal nesting depth (NDPopt in cm) was also negatively related to turbidity as NDPopt = -5.133 Turb + 154.660 (R2 = 0.509). Mean relative reservoir water level fluctuation [RRLF = (Mean reservoir level amplitude/Mean depth) x 100] had a significant negative relationship with ND according to ln ND = -1.185 ln RRLF + 5.231 (R2 = 0.518). As hydrological regimes in reservoirs are mainly influenced by irrigation requirements of command areas, effective dialog between multiple users of reservoirs to achieve a win-win situation could possibly be adopted to optimise fish yield.