Abstract
A study on the effects of introduction of carp-SIS polyculture system on pond fish production, nutritional security and socioeconomic benefit of the rural people has been carried out from 1999 to 2002 with the motivation that the vitamin A and micronutrients deficiencies of the people of Bangladesh can be met by incorporating small fish in the carp polyculture technology in resource poor farmers' ponds. Four polyculture trials with different combinations of carps (Indian major and Chinese) and small indigenous fish species (SIS), mola (Amblypharyngodon mola) and chela (Chela cachius) and a survey on the fish consumption and socioeconomic aspects to assess the impacts of new carp-SIS polyculture technology were basis of this study. In the first experiment, the production performance of mola (Amblypharyngodon mola) and chela (Chela cachius) with carps, rohu (Labeo rohita), catla (Catla catla), mrigal (Cirrhinus mrigala) and grass carp (Ctenopharyngodon idella) in polyculture was evaluated. The stocking density of carps was @ 10,000 fish ha⁻¹ and small fish was @ 25,000 fish ha⁻¹. The production of fish over a period of 210 days ranged from 2,176 to 2,560 kg ha⁻¹ in different treatments with the highest production in treatment where mola was included in carp polyculture. It was further revealed that if partial harvesting of small fish could be made, carp-mola polyculture was better among the treatments in terms of biological production, nutrition and economic return.The second experiment with six treatments was carried out with different combinations of carps-rohu, catla, mrigal, grass carp and silver carp (Hypophthalmichthys molitrix) with and without mola. The highest fish production of 2,712 kg ha⁻¹ was obtained in treatment with five species (rohu, catla, mrigal, silver carp and grass carp) of carps and mola, where mola contributed 0.9% (23 kg ha⁻¹) to total production. The next higher production of 2,642 kg ha⁻¹ was obtained from polyculture of four species of carps (rohu, catla, mrigal and grass carp) with mola, where mola contributed 2% (52 kg ha⁻¹). While mola production was relatively high in this combination, production of catla was reduced. Silver carp had lower, but similar production in all treatments irrespective of presence or absence of mola, whereas silver carp had a negative impact on mola which may partially be mitigated using grass carp.