Production of periphyton to enhance yield in polyculture ponds

With a series of experimental treatments conducted at Agriculture and Forestry University, Chitwan, Nepal, we evaluated four variations of carp polyculture systems to develop a cost-effective method to increase fish production and improve farmers’ access to nutrients, as well as help bolster financial gains from these systems. Two separate trials were conducted: one on a research station (on-station), and one in farmer’s ponds (on-farm). The on-station experiment included four treatments: TF (carp+100% supplemental feed), TFS (carp+SIS+100% supplemental feed), TFSP (carp+SIS+50% supplemental feed+bamboo substrate for periphyton enhancement) and TSP (carp+SIS+ bamboo substrate), each done with three replicates. Silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idella), common carp (Cyprinus carpio), rohu (Labeo rohita), and mrigal (Cirrhinus mrigala) were stocked at a ratio of 4:1:4:3:5:5, respectively, at a rate of 15,000 fish/ha. Additionally, 2 small indigenous species (SIS), dedhuwa (Esomus danricus) and pothi (Puntius sophore), were stocked at a ratio of 1:1 and a combined density of 50,000 fish/ha. Carps were fed daily at 1.5 to 3% of body weight for 210 days with dough (mustard oil cake and rice bran (1:1)), or grass (for grass carp). Final weight and yield of common carp was highest in TFSP ponds, indicating common carp use periphyton and reduced supplementary feed to achieve comparable growth and yield to that of other species being fed completely on supplemental feed. Total carp yield and FCR were highest in TFSP ponds. Gross margin was also highest in treatments enhanced with periphyton (TFSP and TSP). Overall, TFSP was determined the best on-station trial, based on fish total production and profit. The two treatments with the highest net fish yield, TF and TFSP, were introduced to 37 women farmers in Chitwan and Nawalparasi districts for on-farm trials. Farmers prepared TF and TFSP ponds following similar protocols from on-station trials, and stocked carp and SIS. After 8 months of culture, total fish weight and gross margin were 24.0% and 51.2% higher, respectively, in TFSP ponds than in TF ponds. Our results showed that reduced feed application with increased periphyton enhancement dramatically improved profit while maintaining fish yields similar to those of traditional polyculture systems. This method, if adopted by local farmers, could enhance productivity of carp polyculture systems throughout the region.