GROWTH PERFORMANCE OF FISH REARED UNDER DIFFERENT DENSITIES IN SEMI-INTENSIVE AND EXTENSIVE EARTHEN PONDS

Abstract

ffect of stocking density on fish performance has been investigated in earthen ponds over five months of growing period in polyculture system including Nile tilapia, common carp, silver carp, mullet and African catfish. Experimental ponds have been allocated to various stocking rates of 1, 1.25, 1.5, 1.75, 10 and 14 fish/m 3 . The treatments of 10 and 14 fish/m 3 represented the semi-intensive system, while lower densities represented the extensive calture system. Fish in all treatments received 25% crude protein pelleted fish feed at rate of 3% of body weight that was adjusted throughout the growing period. Feed was offered twice/day for five days/week. Water quality has been monitored monthly. The physico - chemical analysis showed two distinct sets of values for the extensive and the semi-intensive stocking densities concurred with for the main water quality parameters, whereas the values of pH, E.C., salinity, alkalinity, hardness, total phosphorus and orthophosphate were significantly higher in extensive system than the semi-intensive one, while values of D.O, SD, NH3, NO2, NO3 were higher in the semiintensive system compared to the extensive system. Plankton communities expressed as Chlorophyll a was significantly higher in the extensive ponds. Average production was significantly higher in semiintensive ponds compared to the extensive ponds. However, for the main fish species (Nile tilapia), the average weight as well as the daily gain did not vary among treatments, while there were some differences with regard to average weight for other species. There was no difference concerning the condition factor in all treatments for any of the tested species. The