Diel Feeding Pattern and Ration of Two Sizes of Tilapia, Oreochromis spp. in Pond and Paddy Field

Abstract

The diel feeding pattern, electivity and ration of tilapia, Oreochromis spp. (4.3-9.3 and 9.5-13.8 cm total length) were investigated to determine the ontogenetic shifts in diet and the importance of habitat on diet and feeding along with water quality characteristics from a nursery pond and a ricefield in Bangladesh. Feeding activity was continuous with diurnal variation in stomach content and per cent of fish feeding. Small tilapia were more active feeders than large ones. Both sizes exhibited a single feeding peak around afternoon-dusk in the pond but irregular feeding peaks in the ricefield. Stomach content did not differ qualitatively with size, ontogenetic shift in diet apparently was lacking, although resource exploitation was different in the two habitats. Periphytic detrital aggregate was the princi­pal diet in the paddy field while filamentous and colonial algae (Anabaena sp. and Melosira sp.) occurring as periphytic epipelon were the main food in the pond. Zooplankton was an insignificant dietary component in both habitats. Oreochrornis spp. was found to be an om­nivorous opportunistic-generalistic benthophagic browser or surface grazer. Its detritivory should not be confused with iliophagy. Feeding intensity and food consumption decreased with the increased fish size. Daily rations for small and large fish were estimated at 2.2 and 2.3% of bw in the pond and 0.91 and 0.45% of bw in the paddy field. Stomach content was computed to be completely evacuated in about 9-13 h in the pond and 1-4 h in the paddy field at water temperatures of 29.0-33.3°C. Total plankton density was higher in the pond than in the ricefield. Phytoplankton densities were higher in the pond while zoop­lankton densities were higher in the ricefield. Water quality properties were well within the acceptable ranges for aquaculture in both habitats. Lack of an ontogenetic dietary shifts suggest that caution should be taken in mixed-size rearing of tilapia.