Evaluation of Presently Practiced Water Exchange Rates on the Performance of Penaeus monodon and on the Water Quality in Semi-Intensive Culture System
U. EDIRISINGHE, J .M.P.K. JAYASINGHE and. P. WANNIGAMA
The Present study was carried out to determine the effects of three different water exchange levels commonly practiced by Sri Lankan farmers on the performance of shrimps and on the water quality in the culture ponds.
Six out-door earthen ponds of approximately 0 .4 ha each with a mean depth of 1.2 meters, located at Arachchikattuwa Chilaw, Sri Lanka were selected. Twenty percent, twenty five percent and thirty percent daily water exchange rates in duplicate were administered in the six ponds randomly where Penaeus monodon was cultured at a density of I5 postlarvae m-2. The physico-chemical parameters examined namely temperature, dissolved oxygen, pH, salinity, BOD5, nitrite, turbidity, total suspended solids, secchi disc visibility and the hydrogen sulphide concentration did not show a significant difference( p>0.05) within the three treatments. Weight gain and the total length of shrimps also did not show a significant difference ( p>0.05) within the three treatments.
According to the results obtained, the economical daily water exchange ate appears to be around twenty percent, Reduction from the thirty percent level to twenty percent will reduce the extraction levels of water from the main resources which are presently overexploited by the rapidly expanding shrimp culture industry.