Efficacy of duckweed (spirodela polyrhiza l. schleiden) in grass carp based semi-intensive carp poly-culture system

摘要

The experiment was conducted to assess comparative efficacy of non-duckweed fed (NDWF) and duckweed (Spirodelapolyrhiza L.Schleiden) fed (DWF) grass carp based semi-intensive carp poly-culture systems, stocked with Indian major carps (Carta carta Ham., Labeo rohita Ham and Cirrhinus mrigala Ham) and exotic carps (Cyprtnus carpio Linn, and Ctenopharyngodon idella Val.) at 10,000 in NDWF group (control) and at 10,000,12,500 and 15,000 in DWF groups (DWF_1, DVVF_2 and DWF_3, respectively). Duckweed feeding did not affect water quality in any of the DWF groups and supported optimum zooplankton production up to stocking density (SD) of 12,500/ha (DWF_2) without any additional manure/fertilizer input As compared to NDWF group, survival of fish remained unaffected in DWF, (SD 10,000/ha) and DWF2 (SD 12,500/ha) groups, but registered a decline in DWF}(SD 15,000/ha). Duckweed feeding supported higher growth in C. carta and C. idella, while growth of both the bottom feeders (C. mrigala and C. carpio) remained unaffected. Significant decline in growth of I. rohita was however, recorded in all the DWF groups. The results reveal that stocking density offish could be enhanced up to 15,000/ha (DWFj) in DWF poly culture system with higher net profit (85.48%) as compared to NDWF poly-culture system. However the maximum net profit (98.36% higher than NDWF), in terms of feed cost reduction (68.83%).