IMPACT OF FERTILIZER ON PRODUCTION OF PRAWN, CARP, AND MOLA IN TRADITIONAL GHER FARMING SYSTEMS OF POOR RURAL FARMERS IN SOUTHWEST BANGLADESH
In the Khulna region of Bangladesh, giant freshwater prawns are co-cultured with carps in paddy fields, a practice known as "gher farming". The farmers, however, are typically unable to invest sufficient amount quality feed due to the associated costs, limiting production and consequently household earnings. We previously established that Mola, a small self-recruiting indigenous fish species of high nutritional value, can be integrated into prawn-carp culture, providing a source of protein and nutrients for farming households to consume without having any negative impacts on prawn production and thus earnings. In the present study, we examined the effectiveness of applying various fertilizers to gher systems in enhancing production of prawn (Machrobrachium rosenbergii), carp (Labeo rohita), and Mola (Amblypharyngodon mola) by increasing natural foods within the ponds. We investigated the following three fertilizer treatments, each of which were applied fortnightly: 15 kg/ha urea and 7.5 kg/ha triple super phosphate (TSP) (T1), fermented mixture of 30 kg/ha molasses and 0.30 kg/ha yeast powder (T2), combination of 50% T1 and 50% T2 (T3), and a control system receiving no fertilizer treatment (T4). The fish were stocked at densities of 2, 0.1, and 2/m2 for prawn, carp, and mola, respectively. Prawn was fed 30% crude protein pelleted feed (2-3% of biomass) three days a week. Prawn production was 459.12±14.6, 471.8±15.6, and 508.8±13.9 kg/ha in T1, T2, and T3 respectively, all of which are significantly higher than the control system (396±17.8 kg/ha) (Table 1). Carp production was also enhanced by the addition of fertilizers with total biomasses of 608±16.47, 589±17.3, 633±15.4 kg/ha in T1-3 relative to 547.6±16.8 kg/ha in the control system. Lastly, Mola production was 401± 11.6, 417 ±15.3, and 440.4±18.4 kg/ha in T1-3 which again was significantly higher than that of the control system (348.4±23.3 kg/ha).
These data indicate that the addition of fertilizers to gher farming systems could be a cost-effective way for rural Bangladeshi farmers to enhance production of prawn-carp-Mola cultures. The highest biomasses were recorded in the T3 ponds, suggesting that a combination of urea, TSP, molasses, and yeast would enhance production of all three species and generate the best economic return for the farmers.
(Supported by the AquaFish Innovation Lab - USAID)