Abstract:
The reproductive biological characteristics of Oreochromis niloticus (Linnaeus 1758) were
investigated in relation to fishing pressure and water level fluctuation in 10 irrigation reservoirs of Sri
Lanka. It was found that matured larger sized male fish made larger and deeper nests. The negative
relationship between gonado-somatic index (GSI) and size of maturity (Lm) of female indicates that
more energy is utilised for gonadal growth of early matured fish. There were negative relationships
of fishing intensity (FI) with egg diameter, Lm, GSI, and condition factor of O. niloticus, showing that
heavy fishing pressure in the reservoir fisheries favoured r-selected life strategies. Based on daily
water level data of reservoirs, an index to express water availability for a sufficient period, making it
possible for the fish to construct nests, termed as water level fluctuation index (WLFI) was calculated.
Nest density during peak spawning period was positively related to WLFI. Hence, it was concluded
that two anthropogenic factors, FI and reservoir water level fluctuations, influenced reproductive
biology attributes of reservoir populations of O. niloticus, which highlighted the necessity for
coordination between fisheries and irrigation authorities for augmenting fish yields.
